CHAPTER - IV ELECTROCHEMICAL BEHAVIOUR OF CALCIUM …shodhganga.inflibnet.ac.in/bitstream/10603/8216/10/10_chapter 4.pdf · The cyclic voltammetric studies of AMLD was carried out

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CHAPTER - IV

ELECTROCHEMICAL BEHAVIOUR OF CALCIUM CHANNEL

BLOCKER DRUGS ON GLASSY CARBON ELECTRODE [GCE]

The most important demands of the pharmaceutical analytical assays are those which

require the measurement of drugs and their metabolites in biological fluids in humans

following administration of low dosage of drugs. Reliable analytical procedures are therefore

needed for their determination. Electrochemical techniques especially, differential pulse

voltammogram/square wave voltammogram is a selective and sensitive method for the

determination of trace level of several drugs in pharmaceutical formulations and urine

samples. This chapter elaborates the results obtained for the evaluation of electrochemical

behaviour of certain calcium channel blockers using glassy carbon as the working electrode.

4.1. ELECTROCHEMICAL STUDIES OF AMLODIPINE (AMLD)

4.1.1. Effect of pH

The influence of pH on the cyclic voltammetric behaviour of AMLD at 100 mV/sec

scan rate was studied. AMLD exhibited characteristic response in the acidic, neutral and basic

pHs. Therefore detailed studies were carried out in the pH region 1.0 to 13.0. In this pH

range, one anodic peak and one broad cathodic peak were observed in the cyclic

voltammograms. In all these cases, the intense and sharp anodic peak appeared in the region

400-1100 mV. The plot of peak current versus pH is given in fig.4.1. From the figure, it is

clear that the anodic current increases with increase in pH. This indicates that the rate of

oxidation of AMLD is increased with pH. It is concluded that pH 13.0 is the most suitable pH

for analytical studies due to maximum peak current. The figure 4.2 represents the peak

potential versus pH plot. The peak potential decreases with increase in pH again suggesting

that the oxidation is facilitated in basic media. The energy required for the oxidation

decreases with increase in pH. The lowest oxidation potential i.e. minimum energy

43

requirement is seen at pH 13.0. Facilitation of oxidation at basic pH due to the availability of

lesser proton is a common expectation for anodic reaction of organics. Then five

representative pHs were selected detailed studies related to the influence of scan rate and

concentration. Detailed cyclic voltammetric studies at selected pH media were carried out and

the results are discussed as follows.

4.1.2. At pH 1.0

The cyclic voltammetric studies of AMLD was carried out at different scan rates,

concentrations and pH using glassy carbon electrode (GCE) and the respective cyclic

voltammograms were recorded. The representative cyclic voltammogram of AMLD is given

in figure 4.3. The peak potentials and current are presented in table 4.1.

The scan rate was varied from 25 to 500 mV/s at five representative pHs and the

cyclic voltammograms were recorded for 410 g/mL of AMLD. The plots of peak current

versus scan rate, square root of scan rate and the logarithmic plot of current versus scan rate

were made. The anodic peak potential shifts anodically with the increase in scan rate. The

anodic peak current versus scan rate plot (Fig.4.4) resulted in a straight line whereas the

current versus square root of scan rate plot resulted in a curved line (Fig.4.5). The logarithmic

plot of current versus scan rate is given in figure 4.6, which is a straight line with slope value

0.6322. This anodic peak didn’t show any reversible peak in the reverse scan. No

characteristic peak satisfying the criteria for reversibility was noticed. The Epa versus log

plot was made and presented in figure 4.7. This plot resulted in a straight line and the n

value was calculated from the slope of the linear plot. The fractional value of (0.665)

indicates the oxidation of AMLD to be irreversible. All the above facts revealed that the

oxidation of AMLD at pH 1.0 was irreversible and adsorption-controlled. The anodic peak

potential and current showed increasing trend with increase in concentration. The plot, peak

current versus concentration is presented in figure 4.8 and it shows linearity.

44

4.1.3. At pH 4.0

The cyclic voltammetric behaviour of AMLD in pH 4.0 medium was studied at a

concentration of 410 g/mL. Here also one anodic peak with high current is observed around

the potential 900 mV in the cyclic voltammograms (Fig. 4.9). The values of peak potential

and peak current are in table 4.2.

The effect of scan rate was studied by varying the scan rate from 25 to 500mV/s. The

oxidation peak was found to shift anodically with increase in scan rate. Peak currents were

correlated with the scan rates and square root of scan rates. A straight line was observed with

the former correlation (Fig.4.4) and curved line was obtained with the later correlation

(Fig.4.5) suggesting adsorption controlled oxidation. Logarithmic values of peak currents

were correlated with the logarithmic values of scan rate and it resulted in straight line

(Fig.4.6). The slope value found from this plot is 0.6184. This again confirms adsorption

controlled oxidation of AMLD in this pH 4.0.

In this case also no cathodic peak was observed in the reverse scan. This shows the

irreversibility of electron transfer. The irreversibility was further confirmed by calculating n

values from the slope of the straight line plot EP vs log (Fig. 4.7). The slope value was

substituted in the following expression for the irreversible charge transfer

dEp /dlog = -30/ n

n is found to be 0.554. The fractional value of n confirms irreversible electron

transfer.

The voltammetric peak current response was correlated with the concentration of the

substrate in the range 68 – 238 g/mL at a scan rate 100 mV s-1

. It also shows linearity

(Fig.4.8) confirming adsorption.

45

4.1.4. At pH 7.0

Various cyclic voltammograms were recorded at different scan rates and different

concentrations at pH 7.0. As in pH 1.0 &4.0, here also one anodic peak around 720 mV was

observed. Figure 4.10 represents a cyclic voltammogram of AMLD at a scan rate of 100

mV/s. Table 4.2 details the results obtained from the scan rate and concentration variation

study. As the scan rate increased from 25 to 500 mV/s, the anodic peak potential increases

from 743.8 to 887 mV. Figures 4.4-4.6 show the plot of peak current versus scan rate (straight

line), peak current versus square root of scan rate (curvature) and log ip versus log (straight

line with slope 0.7710) respectively. The anodic peak potential and peak current increased

with increase in concentration. There was no characteristic reduction peak in the reverse scan

satisfying reversibility. All these facts along with the fractional transfer coefficient value

(0.6503) suggest that oxidation is adsorption controlled and irreversible process at pH 7.0.

Similar correlations were made for the cathodic peak and the figures 4.7-4.8 reveal

that the reduction is irreversible and adsorption controlled.

4.1.5. At pH 9.2

Cyclic voltammetric behaviour of AMLD in pH 9.2 at scan rate 100 mV/s was

presented in fig.4.11. One anodic peak at 594 mV was noticed. Table 4.3 shows the peak

current and peak potential values obtained at different scan rates and different concentrations.

The anodic peak potential and peak current values increased with the scan rate. The

plots of ip versus , ip versus 1/2

, log ip versus log (slope value 0.7409) are given in

figures 4.4-4.6. There is no characteristic reduction peak in the reverse scan satisfying

reversibility. The n value calculated from the slope of potential versus log scan rate plot was

found to be fractional. All these factors reveal that the oxidation is an irreversible adsorption-

controlled reaction. The anodic peak potential and anodic peak current increased with

increase in concentration. Fig. 4.7 and 4.8 represent the correlation plots of AMLD at pH 9.2.

46

4.1.6. At pH 13.0

The cyclic voltammetric behaviour of 410 g/mL AMLD at pH 13.0 on glassy carbon

electrode at a scan rate 100 mV/s was presented in fig.4.12. Similar to other pH media, here

also one anodic peak was noticed. The results observed with scan rate and concentration

variation is presented in table 4.3.

The anodic peak potential shifts anodically with the increase in scan rate. The anodic

peak current versus scan rate plot (Fig.4.4) resulted in a straight line. The current versus

square root of scan rate plot resulted in a curved line (Fig.4.5). The straight-line plot of log

current versus log scan rate with slope value 0.6908 is given in figure 4.6. The anodic peak

potential and current resulted in increasing trend with increase in concentration. The anodic

peak didn’t show any reversible peak in the reverse scan. No characteristic peak satisfying the

criteria for reversibility was noticed. The Ep versus log plot (Fig.4.7) resulted in a straight

line and the n value was calculated from the slope of the linear plot. The fractional value of

transfer coefficient (0.5431) confirmed that the oxidation of AMLD was found to be

irreversible. The peak current versus concentration plot is presented in figure 4.8 and it shows

linearity. All the above facts revealed that the oxidation of AMLD at pH 13.0 was irreversible

and adsorption-controlled.

4.1.7. Controlled potential coulometry

Coulometric ‘n’ value was calculated from the charge consumed by 2.5x10-7

M/dm3

of the substrate to undergo oxidation completely. By substituting the charge in the equation

Q = nFN, where Q is the charge consumed for the oxidation, n is the number of electrons

transferred, F is Faraday and N is the number of moles per equivalent, the n value is

calculated. A typical controlled potential coulomogram is presented in fig.4.13 and the

results are presented in table 4.4. This table shows that the number of electrons transferred is

2 in all pH conditions.

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4.1.8. Mechanism of redox reactions

The cyclic voltammetric evidences presented above reveal that the electrochemical

oxidation of AMLD depends on the pH medium. The number of electrons transferred is 2 in

all pHs. The maximum peak current was observed only at pH 13.0. This is very much

important from the analytical point of view, because the peak produced at this pH is sharp

and intense. The redox mechanism of AMLD at basic medium, pH 13.0 is considered first.

The main oxidation observed around 300 mV is due to the oxidation of amino group present

in AMLD. One primary and one secondary amine are present in the molecule. Both the

primary and secondary amino hydrogens involve in intramolecular hydrogen bonding. Even

though both amino groups have the probability of undergoing 2e- oxidation, the primary

amino group has more probability of easier oxidation. This is because of the fact that the lone

pairs on the secondary amino nitrogen atom delocalize with the conjugated carbonyl system.

This results in lesser availability of loan pair of electrons on the secondary nitrogen atom.

Hence it is proposed that the two electrons are lost from the primary amino group in the main

oxidation. On the basis of the foregoing discussions, the following probable mechanism is

proposed.

4.2. ELECTROCHEMICAL STUDIES OF FELODIPINE (FELD)

Cyclic voltammograms of FELD on glassy carbon electrode at different pH, scan rate

and concentration were recorded and a detailed analysis on the redox behaviour was studied.

The peak potentials and currents were measured and plotted against pH. Similarly, the

48

influences of scan rate and concentration were studied. The background current was recorded

for all reaction conditions and subtracted in the appropriate potential range.

4.2.1. Effect of pH

The effect of pH was studied by varying pH from 1.0 to 13. In the pH range studied

one sharp anodic peak was prominently seen in the cyclic voltammograms in majority of

cyclic voltammograms at different pHs. A broad cathodic peak with higher current but

lacking sharpness was also observed in certain media, mostly acidic and neutral pHs. For

comparative evaluation and characterization at all pHs, the anodic peak was found to be better

than cathodic peak even though it was stronger. Hence, the anodic peak was considered to be

analytical signal and probed further. The peak current was plotted against pH and is given in

the figure 4.14. From the figure it is seen that the peak current increased with increase in pH.

The maximum peak current was obtained at pH 13.0. This shows that the electrochemical

oxidation of FELD is facilitated in basic media and hence the rate of electron transfer is

faster. A plot was made between peak potential and pH and shown in figure 4.15. The peak

potential decreased with increase in pH indicating lower energy requirement for oxidation at

basic pH. In the present study also the same results are observed.

4.2.2. At pH 1.0

An illustrative cyclic voltammogram for 380 g/mL FELD obtained at scan rate 100

mV/s is given in figure 4.16. One anodic peak around potential 1054 mV was observed.

When the scan rate increases the anodic peak shifts anodically. The peak current increased

with increase in the scan rate (Table 4.5). Due to well defined sharp anodic peak with

sufficient peak current response, it was chosen for further analytical studies.

The plot of peak current versus scan rate (Fig. 4.17) resulted in a straight line with

good correlation coefficient (R2

= 0.997). The plot of peak current versus square root of scan

rate exhibited slight curved lines as depicted in fig. 4.18. Of the two plots, the former one

showed good linear correlation suggesting that the oxidation of FELD is adsorption

49

controlled. The plot of log ip versus log is given in fig. 4.19. The slope value 0.6323

suggests that the oxidation of FELD is controlled by adsorption. The anodic peak didn’t show

any cathodic peak in the reverse scan satisfying the reversibility criteria. The Ep versus log

plot (Fig. 4.20) was found to be a straight line and n value calculated from the slope was

found to be fractional (0.4229). Hence, it can be considered that the oxidation of FELD at pH

13.0 was an irreversible and adsorption controlled reaction. Increase in concentration

increased the peak current (Fig.4. 21).

4.2.3. At pH 4.0

By varying the scan rate and concentration, the cyclic voltammetric behaviour of

FELD was studied at pH 4.0 (Table 4.5). Representative CV at this pH 4.0 is given in figure

4.22. One anodic peak around potential 600 mV was observed when the scan rate was varied

from 25 to 500 mV/s and the concentration from 63 to 222 g/mL. Due to high current

response the anodic peak was considered for further studies. The current versus scan rate,

square root of scan rate plots were made and shown in figures 4.17 and 4.18. The former plot

showed better correlation with R2 value equal to 0.999. The slope value (0.7122) obtained

from the logarithmic plot of peak current versus scan rate (Fig.4.19) suggested that the overall

reaction was adsorption controlled. The peak potential correlates well with log scan rate

(Fig.4.20) and resulted in a straight line. The fractional n value (0.5327) calculated from the

slope, along with the absence of reversible couple suggested irreversible electron transfer.

The effect of concentration was studied and the plot of peak current versus concentration is

given in figure 4.21. Both the anodic peak potential and peak current increased with

concentration.

4.2.4. At pH 7.0

Various cyclic voltammograms were recorded at different scan rates at pH 7.0 on

glassy carbon electrode. Here also only one anodic peak was observed at potential around 650

mV (Table 4.5). Figure 4.23 represents a cyclic voltammogram of FELD at pH 7.0. The peak

50

current was correlated with scan rate (Fig.4.17). Less linearity was observed in the correlation

between the peak current and square root of scan rate (Fig.4.18). Plot of log peak current vs.

log scan rate was also linear (Fig.4.19) with a slope 0.5084. These facts confirmed that the

oxidation is adsorption controlled. The correlation between the peak potential and log scan

rate (Fig. 4.20) exhibited a straight line with good correlation. The absence of reversible

couple and the fractional value of n (0.6649), calculated from the slope of the plot suggests

irreversible electron transfer. Concentration of the substrate was varied as in previous pH and

the same trend was observed in the linear plot, peak current against concentration (Fig.4.21).

All these factors revealed that the oxidation of FELD at pH 7.0 was an irreversible and

adsorption controlled reaction.

4.2.5. At pH 9.2

Similar to other pH studies, the effect of scan rate and concentration at pH 9.2 were

carried out. Representative cyclic voltammogram is given in figure 4.24. One anodic peak

around potential 554 mV and one cathodic peak around 770 mV were observed. When the

scan rate increases the anodic peak shifts anodically and cathodic peak shifted cathodically

(Table 4.6). The peak current increased with increase in the scan rate. Due to well defined

sharp anodic peak with sufficient peak current response, it was chosen for further analytical

studies.

Fig.4.17 showed the peak current increased with the increase in scan rate (R2 = 0.997).

A slight curvature was seen in the plot of peak current versus square root of scan rate

(Fig.4.18). The slope of the plot log ipa vs. log scan rate (Fig.4.19) was 0.6756. Plot of

potential versus log scan rate is given in figure 4.20. The n value is calculated from the

slope of the above plot and found to be a fractional value (0.5445). All these facts revealed

that the electrode processes were irreversible and adsorption controlled. Peak current versus

concentration plot is given in figure 4.21, which indicates the increase of peak current with

concentration.

51

4.2.6.. At pH 13.0

The cyclic voltammetric behaviour of FELD at pH 13.0 on glassy carbon electrode at

a scan rate 100 mV/s was given in fig.4.25. One anodic peak at 350 mV and one cathodic

peak at –740 mV in the reverse scan were noticed. The peak potentials and current are

presented in table 4.6.

The anodic peak potential shifts anodically with the increase in scan rate. The anodic

peak current versus scan rate plot (Fig.4.17) resulted in a straight line whereas the current

versus square root of scan rate plot resulted in a curve line (Fig.4.18). The logarithmic plot of

current versus scan rate is given in figure 4.19, which is a straight line with slope value

0.6965. This anodic peak didn’t show any reversible peak in the reverse scan. No

characteristic peak satisfying the criteria for reversibility was noticed. The Ep versus log

plot was made and presented in figure 4.20. This plot resulted in a straight line and the n

value was calculated from the slope of the linear plot. The fractional value of (0.4515)

indicates the oxidation of FELD to be irreversible. All the above facts revealed that the

oxidation of FELD at pH 13.0 was irreversible and adsorption-controlled. The anodic peak

potential and current showed increasing trend with increase in concentration. The peak

current versus concentration plot is presented in figure 4.21 and it shows linearity.


In Controlled potential coulometric method, n value for the compound is determined

from the charge consumed by specific amount of the substrate. The concentrations of the

order 3.5x10-7

M/dm3 of the compound were taken for this study. The coulometric ‘n’ value

was calculated for each compound using the equation Q = nFN. In this case the coulometric

number of electrons transferred is found to be around 2 when the electrolysis is carried out at

350 mV. The CPC data observed and the ‘n’ value calculated for other pH values are given in

table 4.7. A typical controlled potential coulomogram is shown in figure 4.26.

52

4.2.8. Reaction mechanism

Mechanisms of reduction reactions are postulated according to voltammetric studies

and controlled potential coulometry. At basic pH, 2e- irreversible oxidation takes place. As

discussed in the case of FELD, the oxidation may be due to deelctronation of amino group

present in the molecule. The oxidation of other groups requires less energy and hence they

may appear at less positive potentials.

The broad cathodic peak observed in many pHs may be due to the reduction of the

conjugated carbonyl system.

4.3. ELECTROCHEMICAL STUDIES OF LERCANIDIPINE (LERD)

Cyclic voltammograms of LERD on GCE in acid, neutral and alkaline media, at

different scan rates from 25 to 500 mV/s were recorded. The background current was

recorded for all scan rates and subtracted in the appropriate potential range. The peak

potential Ep and peak current ip for respective concentrations and scan rates were measured.

The data obtained are presented and discussed here. A probable redox mechanism is also

arrived.

4.3.1. Effect of pH

The cyclic voltammetric studies of LERD were carried out in the pH range 1.0 to 13.0

and five representative pHs were chosen for study. At all pH viz. 1.0, 4.0, 7.0, 9.2 and 13.0,

one anodic peak and one cathodic peak in the reverse scan were observed. Even though, the

53

broad cathodic peak was observed in many pHs, its broadness and measurement of current

peak current became difficult. Hence, for comparative evaluation and characterization, the

anodic peak observed at all pHs considered for further studies to probe the oxidation

mechanism. For the study of influence of pH on the cyclic voltammetric response, five pH

viz. 1.0, 4.0, 7.0, 9.2 and 13.0 were chosen and the cyclic voltammograms were recorded for

610 g/mL LERD at a scan rate of 100 mV/s. The peak currents and peak potentials were

plotted against pH and the plots are given in figures 4.27 & 4.28 respectively. The peak

current increased with increase in pH. The maximum peak current response was found in pH

13.0. This is due to faster electron transfer at pH 13.0 and indicates that the electrochemical

oxidation of LERD is facilitated in basic media. Hence it can be considered as an optimum

pH for the study of LERD. The peak potential decreased with increase in pH. The peak

potential of anodic peak shifted anodically with pH whereas that of cathodic peak shifted

cathodically with pH. The cathodic peak potential and peak current shifted cathodically with

increase in pH.

4.3.2. At pH 1.0

An aqueous alcoholic solution of 0.1 M H2SO4 was chosen as the medium for the

study. Fig. 4.29 represents the cyclic voltammogram of LERD recorded at pH 1.0. One

anodic peak was observed at the potentials around 1060 mV. In the reverse scan one cathodic

peak was observed around 540 mV. Peak potentials and peak currents for all voltammograms

are presented in table 4.8. The effect of scan rate was studied for the anodic peak at a scan

rate from 25 to 500 mV/s. The peak current was plotted against scan rate (Fig. 4.30) and

resulted in a straight line whereas the peak current increased non-linearly with square root of

scan rate (Fig. 4.31). The log ip vs. log plot (Fig. 4.32) yielded a straight line with slope

0.6212. These facts revealed the nature of electrode reaction as adsorption controlled. The

variation of peak potential with log scan rate (Fig. 4.33) resulted in a straight line ( n =

0.8855). The potential difference between the anodic peak and the cathodic peak was high.

54

Hence, it can be considered that the oxidation of LERD at pH 1.0 is irreversible. The effect of

concentration on peak current at a constant scan rate 100 mV/s was carried out by changing

the concentration from 111 to 356 g/mL. Increase in the concentration of LERD showed

increase in the peak current as well as increase in peak potential. The plot of ip vs.

concentration (Fig. 4.34) yielded a straight line. Hence, it may be concluded that at pH 1.0,

irreversible adsorption controlled oxidation reactions.

4.3.3. At pH 4.0

Fig. 4.35 represents the cyclic voltammogram recorded at pH 4.0. Similar to the

previous pH, here also one anodic peak and one cathodic peak in the reverse scan were

observed around potentials 150 mV and –850 mV respectively. It can be seen that the anodic

peak potential shifted cathodically when compared to the pH 1.0. Also the sharpness of the

peaks was lost when compared to the pH 1.0. Hence the values of the main anodic peak

potentials and current are given table 4.9. The scan rate was varied between 25 and 500 mV/s.

The peak current versus scan rate and square root of scan rate plots were made (Fig.4.30 &

4.31). Similar trend was observed as in the previous pH 1.0. The former plot resulted in a

straight line and the latter plot showed non linearity. The plot of log current versus log scan

rate (Fig.3.32) resulted in a straight line with slope value 0.5729. All the above facts revealed

that the oxidation of LERD was adsorption controlled at this pH. The impact of log scan rate

on the peak potential showed linear shift for the anodic peak (Fig.4.33). The anodic peak and

the cathodic peak did not satisfy the criteria for reversibility. Hence, it can be considered that

the reaction is an irreversible one. The concentration was varied as in the previous pH 1.0 and

the effect on peak current was observed. From the linear plot of peak current versus

concentration (Fig.4.34) it can be seen that the peak current increased with concentration.

4.3.4. At pH 7.0

The peak potential and peak current values observed for the variation in scan rate and

concentration are given in table 4.9 and representative voltammogram is given in figure 4.36.

55

The peak current versus scan rate, peak current versus square root of scan rate for the anodic

peak were made (Fig. 4.30 & 4.31). The former plot resulted in a straight line whereas the

latter plot was non-linear with less correlation. The logarithmic plot of peak current versus

scan rate (Fig.4.32) resulted in a straight line with R2 value equal to 0.998. The slope was

found to be 0.6236. Hence the overall reaction is considered to be adsorption controlled. The

plot of peak potential versus log scan rate resulted in a straight line and is given in figure

4.33. The anodic peak and the cathodic peak did not satisfy the criteria for reversibility.

Hence, it is considered that the oxidation of LERD is irreversible and adsorption controlled at

pH 7.0. Linear plot of peak current versus concentration (Fig.4.34) showed the increase in

peak current with concentration.

4.3.5. At pH 9.2

Aqueous alcoholic solution of Britton-Robinson buffer pH 9.2 was prepared and used

as the medium for the study. Only one anodic peak and one cathodic peak were observed

when the studies were made at different sweep rates and concentrations. As an illustration,

cyclic voltammogram of LERD at pH 9.2 is presented in figure 4.37. The peak potential and

current values are given in table 4.10.

The sweep rate was changed over a range from 25 to 500 mVs–1

for 356 µg/mL

concentration. As the sweep rate was increased, the peak current increased gradually and the

peak potential shifted anodically. The peak current increased linearly with the sweep rate,

and led to a straight line (Fig. 4.30) and was non-linear with the square root of sweep rate

(Fig.4.31). The log ip vs. log plot (Fig.4.32) had a slope value of 0.6071. These observed

facts revealed an adsorption-controlled reaction. The peak current also varies linearly with

concentration (Fig. 4.34). Absence of peak in the reverse scan and fractional n value that

was calculated as usual from the straight-line plot of Ep vs. log (Fig. 4.33) indicates the

irreversible electron transfer.

56

4.3.6. At pH 13.0

0.1 M NaOH in aqueous alcohol was used as the medium. Only one anodic peak was

observed around 600 mV. A representative cyclic voltammogram is presented in figure 4.38

and the results are presented table 4.10.

For 356 µg/mL concentration of LERD, as the sweep rate increased the peak current

increased for the oxidation peak. The peak potential shifts anodically. The intensity of the

peak is a linear function of the scan rate and non-linear with square root of the scan rate. This

was evident from the plot of ip vs. sweep rate and square root of sweep rate (Fig. 4.30 &

4.31). The slope of the log ip vs. log plot (Fig. 4.32) is 0.6329. The peak current versus

concentration plot (Fig. 4.34) is also a straight line with good correlation. The n value

calculated from the slope of the straight-line plot, Ep vs. log (Fig. 4.33) was also found to be

a fraction. (0.5947). All these facts revealed adsorption controlled irreversible reaction.


Controlled potential coulometry was performed at pH 13.0 in the same cell setup. The

coulometric ‘n’ value was determined after exhaustive electrolysis 10 ml of 3.5x10-7

M/dm3

LERD solution (pH 13.0) and it was found to be 2 (Fig.4.39). This indicates the two-electron

transfer in the electrooxidation of LERD. Table 4.11 listed the data obtained in other pH

media.


The mechanism of main oxidation may be assigned to the oxidation of secondary

amino group which at pH 13.0 underwent redox reaction.

57

The cathodic peak observed cyclic voltammograms recorded at acidic and neutral pHs

may be due to the reduction of the conjugated carbonyl system.

4.4. ELECTROCHEMICAL STUDIES OF NIFEDIPINE (NIFD)

The cyclic voltammetric behaviour of NIFD was studied at different scan rates and

concentrations and pH using glassy carbon electrode (GCE) and the respective cyclic

voltammograms were recorded. The studies were carried out in the pH range 1.0 to 13.0 and

detailed studies related to the influence of scan rate and concentration were carried out.

4.4.1. Effect of pH

Cyclic voltammograms obtained for 350 g/mL NIFD at 100 mV/s were recorded in

pH range 1.0 to 13.0. NIFD is active in acid, neutral and basic pH and exhibits one anodic

peak and one broad cathodic peak in the reverse scan in acidic pH. In all other pHs, only

anodic peak is observed. For comparative evaluation and characterization at all pHs, the

anodic peak was found to be better than the broad cathodic peak observed only in limited

pHs. Hence, it was considered as an analytical signal. The peak current and peak potential

values were correlated with pH. The plot of peak current versus pH is given in figure 4.40.

The figure shows a decrease in peak current with increase in pH upto neutral conditions and

then increase with pHs. The maximum peak current was observed at pH 13.0. This indicated

that the rate of oxidation of NIFD is more in basic media. The non-linear plot of peak

potential versus pH is shown in figure 4.41.

4.4.2. At pH 1.0

The peak currents and peak potentials from the cyclic voltammograms obtained for

NIFD at different scan rates and different concentrations were listed in table 4.12. As an

illustration, the cyclic voltammogram obtained for NIFD at this pH is shown in figure 4.42.

The anodic peak was observed at potential around 1094 mV and the cathodic peak at –433.5

58

mV. Since the cathodic peak was observed only under acidic conditions, the anodic peak was

considered for further studies. With the increase in the scan rate from 25 to 500 mV/s, the

anodic peak potential shifted anodically. The plot of peak current versus scan rate was given

in fig 4.43, which was a straight line. The curve line of peak current versus square root of

scan rate was given in fig. 4.44. The logarithmic plot of peak current versus scan rate is given

in fig.4. 45. The slope value of the plot was 0.5768. This indicated the adsorption-controlled

oxidation of NIFD. The anodic peak and cathodic peak did not satisfy the reversibility

criteria. The fractional n value (0.4378) calculated from the plot of peak potential versus log

scan rate (Fig.4. 46) indicated the irreversibility of the reaction. By varying the concentration

of the substrate from 58 to 204 g/mL, the cyclic voltammetric behaviour at 100 mV/s scan

rate was studied. The linear plot of peak current versus concentration (Fig. 4.47) showed the

linearity between both. The peak potential also increased with the concentration.

4.4.3. At pH 4.0

As in pH 1.0, here also the cyclic voltammetric studies were carried out at different

scan rates and different concentrations. An illustrative cyclic voltammogram at pH 4.0 on

glassy carbon electrode is given in figure 4.48. One anodic peak around 130 mV and one

cathodic peak around –720 mV were noticed. The data obtained for the variation of scan rate

and concentration is listed in table 4.12. The anodic peak current was higher when compared

to the pH 1.0. The plots peak current versus scan rate (straight line), peak current versus

square root of scan rate (curve line), log peak current versus log scan rate (slope = 0.5697)

presented in figures 4.43-4.45 revealed that oxidation of NIFD is controlled by adsorption.

The plot of potential versus log scan rate is given in figure 4.46. From the slope of the

straight-line plot the transfer coefficient was calculated and found to be fractional (0.7214)

which indicated the irreversible electron transfer. Increase in concentration increased the peak

current linearly (Fig. 4.47).

59

4.4.4. At pH 7.0

The cyclic voltammograms at different concentrations and different scan rates were

recorded. The results are listed in table 4.12. One anodic peak around the potential 65 mV

was observed. Small cathodic peak was noticed in the reverse scan at -625 mV. The

representative cyclic voltammogram is given in fig. 4.49. Straight line is noticed when the

peak current was plotted against the scan rate (Fig. 4.43). A non-linear with less correlation

was observed for the plot of peak current versus square root of scan rate (Fig. 4.44). Linear

plot of log peak current versus log scan rate (Fig. 4.45) with slope value 0.5982 indicated that

the oxidation of NIFD is adsorption controlled. The peak potential versus log scan rate

resulted in a linear plot (Fig. 4.46). The absence of cathodic peak in the reverse scan showed

that the mechanism involved is an irreversible oxidation. The effect of concentration was

studied by varying the concentration at constant scan rate 100 mV/s. The plot of peak current

versus concentration (Fig. 4.47) was made. From the figure it can be seen that there is an

increase in peak current with increase in concentration.

4.4.5. At pH 9.2

As in the above pH media, here also the studies were carried out. Similar to the pH

9.2, only the anodic peak was observed and no cathodic peak in the reverse scan. The peak

current and peak potential values were recorded for sweep rate and concentration variation

and listed in table 4.13. The figure 4.50 illustrates the representative cyclic voltammogram.

The effect of scan rate was studied in the range 25 to 500 mV/s. The observations were

discussed as follows. The anodic peak potential increases with increase in scan rate. The plot

of peak current versus scan rate and peak current versus square root of scan rate are given in

figures 4.43 & 4.44. The previous plot showed better correlation with R2 value 0.9996. The

plot of log current versus log (Fig. 4.45) results in a straight line with slope value 0.5944.

The above facts revealed that the oxidation of NIFD is adsorption-controlled. The Ep versus

log plot (Fig. 4.46) resulted in a straight line. No cathodic peak in the reverse scan was

60

observed. Hence it is considered that the oxidation of NIFD involves irreversible electron

transfer. The plot of peak current versus concentration was given in fig. 4.47. The anodic

peak potentials shift anodically and peak current also increases with increase in

concentration.

4.4.6. At pH 13.0

0.1 M NaOH in aqueous alcohol was used as the medium. One anodic peak and one

cathodic peak were observed around 400 mV and 650 mV. Among the peaks anodic peak was

shows high current it is used for further discussion. A representative cyclic voltammogram is

presented in figure 4.51 and the results are presented table 4.13.

For 350 µg/mL concentration of NIFD, as the sweep rate increased the peak current





concentration plot (Fig. 4.47) is also a straight line with good correlation. There was no

cathodic response in the reverse scan. The n value calculated from the slope of the straight-

line plot, Ep vs. log (Fig. 4.46) was also found to be a fraction. (0.5447). All these facts

revealed adsorption controlled irreversible reaction.


The number of electrons transferred in the oxidation process was determined by

employing Controlled potential coulometry. The charge consumed by 2.5 x 10-7

M/dm3

concentration of NIFD was measured from the coulomogram. The coulometric ‘n’ value was

calculated for each compound using the equation Q = nFN. In this case the coulometric

number of electrons transferred is found to be around 2 when the electrolysis is carried out at

400 mV. The CPC data observed and the ‘n’ value calculated for other pH values are given in

table 4.14. A representative coulomogram is presented in figure 4.52.

61


The electroactive group in NIFD is similar to that of FELD. Hence the same

mechanism may be proposed for the oxidation of NIFD.

4.5. ELECTROCHEMICAL STUDIES OF NIMODIPINE (NIMD)

The cyclic voltammetric behaviour of NIMD in different pHs between 1.0 and 13.0 at

various scan rate and concentration range was investigated. The influence of pH, scan rate

and concentration on the peak current and peak potential were studied.

4.5.1. Effect of pH

Cyclic voltammograms were recorded in the pH range 1.0 to 13.0. One anodic peak

was observed at all the pHs and a broad cathodic peak was seen in the reverse scan at certain

pHs. Since the anodic peak was found to be sharp and had characteristic peak current under

all the experimental conditions, it was considered for probing the mechanism of oxidation. As

the pH increased, the peak current of anodic response decreased initially up to pH 7.0 and

then increased (Fig. 4.53) steadily. The maximum peak current was observed in pH 13.0. The

pH 13.0 was selected to be the analytical signal. This indicates that the rate of oxidation of

NIMD more in basic media. The non-linear plot of peak potential versus pH is shown in

figure 4.54.

62

4.5.2. At pH 1.0

Figure 4.55 represents the cyclic voltammogram of NIMD at 100 mV/s in pH 1.0. The

anodic peak was observed in the potential around 650 mV. The anodic peak potentials shifted

anodically with the increase in scan rate. The results are listed in table 4.15. The current

versus scan rate plot (Fig.4.56) was made. The plot resulted in a straight line with good

correlation (R2 = 0.998). Slightly curved line was obtained for the plot peak current versus

square root of scan rate (Fig. 4.57). The logarithmic plot of peak current versus log scan rate

with a slope value of 0.615 was shown in fig. 4.58. These facts revealed that the oxidation of

NIMD is adsorption controlled. The Ep versus log scan rate plot is given in figure 4.59. The

n value calculated from the slope of the plot was fractional (0.5031). The anodic peak and

the cathodic peak did not satisfy the criteria for reversibility. Hence it is concluded that the

oxidation involves irreversible electron transfer. Also the concentration was varied from 70 to

245 g/mL at constant scan rate of 100 mV/s. The peak current showed increasing trend with

increase in concentration (Fig. 4.60).

4.5.3. At pH 4.0

Similar to pH 1.0, the effect of scan rate and concentration on the peak potential and

peak current was studied. The cyclic voltammogram of NIMD at this pH is presented in

figure 4.61. Here also anodic peak is prominent. The values of peak current and potential

were listed in table 4.15. The current versus scan rate plot (Fig 4.56) results in a straight line

(R2

= 0.9991). The plots of peak current versus square root of scan rate and log ip versus log

were shown in fig.4.57 & 4.58. The slope value got from the latter plot was 0.6027, which

indicates the adsorption-controlled oxidation of the NIMD. From the slope of the straight-line

plot, peak potential versus log scan rate (Fig. 4.59) the n value was calculated to be 0.7403.

Also the anodic peak and the cathodic peak did not satisfy the reversibility criteria. Hence the

oxidation is proposed to undergo irreversible electron transfer. The effect of concentration

63

was studied as in the previous case. The linear plot of peak current versus concentration (Fig.

4.60) showed the increase in anodic peak current with concentration.

4.5.4. At pH 7.0

Figure 4.62 represents the cyclic voltammogram of NIMD observed at 100 mV/s scan

rate in pH 7.0. At this pH also one anodic peak was observed around potential 170 mV and

one cathodic peak was broad. The peak potentials and currents are given in table 4.15.

Considering the well-defined anodic peak, correlation studies were done for this peak

response only. Figures 4.56 & 4.57 represent the plot of peak current versus scan rate

(straight line with R2 = 0.9978) and peak current versus square root of scan rate (slightly

curved). The slope (0.7266) of the linear plot log ip versus log Fig. 4.58) indicate the

adsorption-controlled oxidation of NIMD. The plot of peak potential versus log scan rate

(Fig. 4.59) was made and resulted in a straight line. From the slope of the plot n value was

calculated to be 0.5558. The anodic peak and the cathodic peak did not follow the

reversibility criteria. The effect of concentration was studied. The anodic peak potential shifts

anodically with the increase in concentration. The peak current also increased with

concentration and is shown in figure 4.60. Thus it is concluded that the oxidation of NIMD is

irreversible and adsorption controlled.

4.5.5. At pH 9.2

The cyclic voltammogram of NIMD obtained at pH 9.2 is presented in figure 4. 63.

One anodic peak and a broad cathodic peak were observed. The anodic peak was found to be

sharp in pH 9.2. Increase in peak current was noted for anodic peak when compared to that at

other pH conditions. Anodic response was found to be sharp. The results of cyclic

voltammetric data obtained are presented in table 4.16. The effect of scan rate was studied in

a similar way as in the previous pH by keeping the concentration at 420 µg/mL. Peak current

increased with increase in scan rate. Plot of peak current vs. scan rate showed linearity (Fig

4.56). The plot of ip vs (Fig 4.57) resulted in a curve line. Log values of peak current

64

were plotted with log of scan rate and straight line was obtained (Fig 4.58). The slope value

was 0.6973. Here also the oxidation was adsorption controlled.

The n value calculated from the plot, peak potentials vs. log values of scan rates (Fig

4.59) was found to be a fraction (0.4964) revealing irreversible electron transfer. The effect of

concentration was studied as in previous pHs. Increasing concentration increased the peak

current with anodic shift in peak potential (Fig 4.60).

4.5.6. at pH 13.0

A typical cyclic voltammogram of NIME obtained at pH 13.0 is presented in figure

4.64. Here also one anodic peak and one broad cathodic peak were observed. The cyclic

voltammetric data acquired are presented in table 4.16. The effect of scan rate was studied as

in the previous pHs at a concentration of 420 µg/mL. The peak current increased with

increase in scan rate. The plot of peak current vs. scan rate showed linearity with good

correlation (Fig. 4.56). The dependence of peak current on square root of scan rate (Fig. 4.57)

was curve line with lower correlation than previous case. Log values of peak current were

correlated with log scan rate to produce a straight line was obtained (Fig. 4.58). The slope

value, 0.6897 confirmed adsorption controlled reduction.

Increasing concentration resulted in increase in peak current. There was no

appreciable anodic shift in peak potential (Fig. 4.59). The n value calculated from the plot,

peak potentials vs. log values of scan rates (Fig. 4.60) was found to be a fraction (0.6206)

confirming irreversible nature of the reaction.


Controlled potential coulometry was performed by employing 2.1 x 10-7

M/dm3 of

NIMD concentration in pH 13.0 (Fig. 4.65). The coulometric ‘n’ value was determined after

exhaustive electrolysis and it was found to be two. The data obtained at other pH media is

given in table 4.17.

65


As in NIFD, here also similar results were obtained. Thus the oxidation may be

assigned to the oxidation of secondary amino group in NIMD. At basic pH the following

mechanism of oxidation is proposed.

4.6. ELECTROCHEMICAL BEHAVIOUR OF NITRENDIPINE (NITD)

Cyclic voltammetric studies of were carried out at various pHs ranging from 1.0 to

13.0. As in previous drug, five representative pH media were chosen and detailed studies

were made. The results of these studies are discussed as follows.

4.6.1. Effect of pH

In order to study the effect of pH, thirteen pH media were chosen in the pH range

from 1.0 to 13.0. Cyclic voltammograms were run at all the pH conditions using 360 µg/mL

concentration of NITD at a sweep rate of 100 mV/s. The peak potential and current were

measured and correlated with pH. Except acidic pHs, in all other pHs, only anodic peak was

observed whereas in acidic pHs, a broad cathodic peak was also observed additionally. Figure

4.66 represents the effect of pH on the peak potential. As the pH increased, the peak potential

decreased. The oxidation was facilitated in basic medium due to the reason that lesser

electrochemical energy is required for the oxidation in basic medium. The peak current

decreased with an increase in pH up to pH 7.0 and then increased with an increase in pH (Fig.

4.67). The maximum peak current was noticed only at base pH 13.0. The peak shape,

sharpness and current led to the selection of the pH 13.0 as the best pH for the

electroanalytical studies.

66

4.6.2. At pH 1.0

Cyclic voltammetric behaviour of NITD in the concentration range 60-210 µg/mL in

aqueous alcoholic pH 1.0 was studied. At all concentrations and at different sweep rate

change, the compound showed one well-defined anodic peak around 1010 mV and one

cathodic peak at 500 mV. Representative cyclic voltammogram is presented in figure 4.68

and entire results are presented in table 4.18.

4.6.2.1. Effect of sweep rate

At a concentration of 360 µg/mL of the compound NITD, the sweep rate was varied

from 25 to 500 mV/s. As the sweep rate increased the peak current increased while the peak

potential shifted anodically. The extent of peak potential shift was used to determine n. The

magnitude of peak current was a linear function of sweep rate but non–linear in square root of

sweep rate as it was evidenced from ip vs. and ip vs.

1/2 plot (Fig. 4.69 & 4.70). The log ip

vs. log sweep rate (Fig. 4.71) exhibited linearity with a slope of 0.5861. These observations

focus the voltammetric oxidation as adsorption controlled.

4.6.2.2. Irreversibility

Throughout the region of study, there was a cathodic peak obtained in reverse scan

but didn’t fulfill irreversible criteria. This shows irreversible nature electron transfer. The

irreversibility observed in all the cases was confirmed by calculating the values of n from

the slope obtained from the Ep vs. log plot, (Fig. 4.72). n obtained by this procedure is

found to be 0.5244.

4.6.2.3. Effect of concentration

The effect of change in concentration of the substrate was studied by changing the

concentration from 60 to 210 µg/mL at a selected sweep rate, 100 mVs–1

. The peak current

gradually increased. The peak potential shifted in anodic direction. The peak current showed

linearity with concentration resulting in good correlation (r2 = 0.992) (Fig. 4.73).

67

4.6.3. at pH 4.0

Cyclic voltammograms of NITD in aqueous alcoholic Britton-Robinson buffer (pH

4.0) medium were recorded at different scan rates from 25 to 500 mV/s. One well-defined

anodic peak and one cathodic peak were observed under the above said experimental

conditions. A representative cyclic voltammogram is given in figure 4.74. The voltammetric

results obtained are presented in table 4.18.

4.6.3.1. Effect of sweep rate

As the sweep rate increased the peak current increased. The potential shifts in the

anodic direction. The dependence of peak current on the sweep rate is well understood from

the straight-line plot shown in figure 4.69. And the peak current vs. square root of sweep rate

is non-linear (Fig.4.70). The slope of the straight-line plot between log ip and log (Fig.

4.71) is 0.6873. These behaviours are indicating adsorbed controlled electrode reaction.

4.6.3.2. Irreversibility

In all the cases, no cathodic current is observed in the reverse scan. This shows the

irreversibility of electron transfer. As discussed earlier, the n value that is calculated from

the slope of the straight line obtained in the plot Ep vs. log (Fig. 4.72) is found to be 0.5995.

Fractional n value confirms the irreversibility of the electron transfer.

4.6.3.3. Effect of concentration

To study the effect of concentration on the voltammetric behaviour, concentration of

the substrate was increased from 60 to 210 µg/mL keeping the sweep rate constant at 100

mVs–1

. Increase in peak current and anodic shift in peak potentials were the results of an

increase in the concentration. Plot of peak current vs. concentration is presented in figure

4.73. Straight line with good correlation is obtained, (r2= 0.9952).

All the above facts reveal that electrooxidation of NITD using glassy carbon electrode

at pH 4.0 is controlled by adsorption. The electron transfer is irreversible.

68

4.6.4. At pH 7.0

Cyclic voltammograms were recorded for the sample under study in 0.1 M aqueous

alcoholic potassium chloride medium by changing the sweep rate and concentrations. Here

also one peak and one cathodic peak were observed at all experimental conditions. The peak

potential and current values are presented in table 4.18. Typical cyclic voltammogram is

presented in figure 4.75.

A study on the influence of the sweep rate on the peak current within the range, 25 to

500 mV/s showed that the peak current is linearly dependent on the sweep rate and non-linear

in square root of peak current. The plot of ip vs. sweep rate (Fig. 4.69) resulted in a straight

line with good correlation, (r2 = 0.9923) where as that of ip vs. square root of peak current

resulted in a non-linear plot (Fig.4.70). The peak potential shifted moderately in the anodic

direction with increase in sweep rate. The slope of the straight line obtained from the plot, log

ip vs. log (Fig. 4 .71) is 0.667.

In all the cases cathodic current response was found in the reverse sweep but didn’t

satisfy irreversible criteria. n values calculated from Ep vs. log plot (Fig. 4.72) was

fractional ( n = 0.7136) indicating irreversibility. In this pH also, the reaction is adsorption

controlled and irreversible. Increased peak current values and anodic shift were observed with

increase in concentration of nitrendipine. Plot of ip vs. C (Fig. 4.73) led to a straight line.

4.6.5. At pH 9.2

Aqueous alcoholic solution of Britton-Robinson buffer pH 9.2 was prepared and used

as the medium for the study. Only one anodic peak and one cathodic peak were observed

when the studies were made at different sweep rates and concentrations. As an illustration,

cyclic voltammogram of nitrendipine at pH 9.2 is presented in figure 4.76. The peak potential

and current values are given in table 4.19.

The sweep rate was changed over a range from 25 to 500 mV/s for 360 µg/mL

concentration. As the sweep rate was increased, the peak current increased gradually and the

69

peak potential shifted anodically. The peak current increased linearly with the sweep rate,

and led to a straight line (Fig. 4.69) and was non-linear with the square root of sweep rate

(Fig.4.70). The log ip vs. log plot (Fig.4.71) had a slope value of 0.6371. These observed

facts revealed an adsorption-controlled reaction. The peak current also varies linearly with

concentration (Fig. 4.73). Cathodic peak is not satisfied for irreversibility and fractional n

value that was calculated as usual from the straight-line plot of Ep vs. log (Fig. 4.72)

indicates the irreversible electron transfer.

4.6.6. At pH 13.0

0.1 M NaOH in aqueous alcohol was used as the medium. Only one anodic peak and

one cathodic peak were observed around 436 mV and 717 mV respectively. A representative

cyclic voltammogram is presented in figure 4.77 and the results are presented table 4.19.

For 360 µg/mL concentration of NITD, as the sweep rate increased the peak current





concentration plot (Fig. 4.73) is also a straight line with good correlation. There was a

cathodic response in the reverse scan but didn’t fulfill irreversibility. The n value calculated

from the slope of the straight-line plot, Ep vs. log (Fig. 4.72) was also found to be a fraction.

(0.4547). All these facts revealed adsorption controlled irreversible reaction.

4.6.7. Controlled Potential Coulometry

A concentration of the order 2.0x10-6

mM.dm–3

of NITD was taken for the controlled

potential electrolysis at the selected medium (pH 13.0). The coulometric ‘n’ value was

calculated for each pH using the relation Q = nFN. Experimental findings are presented in

70

table 4.20. The charge vs. time plot is shown in figure 4.78 as a representative case. The

coulometric number of electrons transferred was found to be two.

4.6.8. Mechanism of Oxidation

As in many of the calcium channel blockers discussed previously, here also a similar

mechanism may be proposed for the two electron electrooxidation of NITD.

The results obtained from cyclic voltammetric studies of the selected drugs on plain

GCE at various pHs, scan rate and concentration paved way for the selection of pH and

characteristic analytical signal. These fundamental studies constitute the basis for the

electrochemical studies of these drugs to find out the efficient modified electrode system for

the development sensitive electroanalytical procedure. As first modification, clay modified

electrode was considered and the results obtained are discussed in the next chapter.

71

0

2

4

6

8

0 2 4 6 8 10 12 14pH

i(A

)

Figure 4.1. Plot of peak current versus pH

300

500

700

900

1100

0 2 4 6 8 10 12 14pH

E(m

V)

Figure 4.2. Plot of peak Potential versus pH

-31

-11

9

29

-0.9 -0.35 0.2 0.75 1.3

E(V)

ip(

A)

Figure 4.3. Cyclic voltammogram of 410 g/mL amlodipine on GCE at pH 1.0; scan rate 100

mV/s

72

0

4

8

12

16

20

0 100 200 300 400 500(mV/s)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0

Figure 4.4. Plot of peak current vs. scan rate at five different pH media

0

4

8

12

16

20

4 9 14 19 24

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0

Figure 4.5. Plot of peak current vs. square root of scan rate at five different pH media

-0.5

0.0

0.5

1.0

1.5

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

log

ip

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0

Figure 4.6. Plot of log peak current vs. log scan rate at five different pH media

73

350

550

750

950

1150

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

E(m

V)

pH 1.0 pH 4.0 pH 7.0 pH 9.2 pH 13.0

Figure 4.7. Plot of potential vs. log scan rate at five different pH media

0

4

8

12

60 100 140 180 220

Conc(ppm)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0

Figure 4.8. Plot of peak current vs. concentration at five different pH media

-20

-15

-10

-5

0

5

10

15

-0.9 -0.35 0.2 0.75 1.3

E(V)

ip(

A)

Figure 4.9. Cyclic voltammogram of 410 g/mL amlodipine on GCE at pH 4.0; scan rate 100

mV/s

74

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

-0.9 -0.35 0.2 0.75 1.3

E(V)

ip(

A)

Figure 4.10. Cyclic voltammogram of 410 g/mL amlodipine on GCE at pH 7.0; scan rate

100 mV/s

-30

-25

-20

-15

-10

-5

0

5

10

15

20

-0.9 -0.35 0.2 0.75 1.3

E(V)

ip(

A)


100 mV/s

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

-0.9 -0.35 0.2 0.75 1.3

E(V)

ip(

A)


100 mV/s

75

0

50

0 320Time (sec)

Q(m

C)

Figure 4.13. Plot of charge vs. time

0

2

4

6

8

0 2 4 6 8 10 12 14pH

i(A

)


300

500

700

900

1100

0 2 4 6 8 10 12 14pH

E(m

V)


76

-40

-30

-20

-10

0

10

20

30

-1.2 -0.4 0.4 1.2

E(V)

ip(

A)

Figure 4.16. Cyclic voltammogram of 380 g/mL Felodipine on GCE at pH 1.0; scan rate

100 mV/s

0

4

8

12

16

20

0 100 200 300 400 500(mV/s)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


0

4

8

12

16

20

4 9 14 19 24

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


77

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

log

ip

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


300

500

700

900

1100

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

E(m

V)

pH 1.0 pH 4.0 pH 7.0 pH 9.2 pH 13.0


0

4

8

12

60 100 140 180 220

Conc(ppm)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


78

-40

-30

-20

-10

0

10

20

30

-1.2 -0.4 0.4 1.2

E(V)

ip(

A)


100 mV/s

-50

-40

-30

-20

-10

0

10

20

-1.2 -0.4 0.4 1.2E(V)

ip(

A)


100 mV/s

-50

-40

-30

-20

-10

0

10

20

-1.2 -0.4 0.4 1.2

E(V)

ip(

A)


100 mV/s

79

-50

-40

-30

-20

-10

0

10

20

30

-1.2 -0.7 -0.2 0.3 0.8

E(V)

ip(

A)


100 mV/s

0

100

0 320Time (sec)

Q(m

C)


2

4

6

8

0 2 4 6 8 10 12 14pH

i(A

)


80

0

300

600

900

1200

0 2 4 6 8 10 12 14pH

E(m

V)


-60

-39

-18

3

24

45

-1 -0.2 0.6 1.4E(V)

ip(

A)

Figure 4.29. Cyclic voltammogram of 356 g/mL lercanidipine on GCE at pH 1.0; scan rate

100 mV/s

0

4

8

12

16

20

0 100 200 300 400 500(mV/s)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


81

0

4

8

12

16

20

4 9 14 19 24

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

log

ip

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


0

300

600

900

1200

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

E(m

V)

pH 1.0 pH 4.0 pH 7.0 pH 9.2 pH 13.0


82

0

4

8

12

16

20

100 200 300 400

Conc(ppm)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


-60

-39

-18

3

24

-1.2 -0.7 -0.2 0.3 0.8

E(V)

ip(

A)


100 mV/s

-60

-39

-18

3

24

-1.2 -0.7 -0.2 0.3 0.8

E(V)

ip(

A)


100 mV/s

83

-60

-39

-18

3

24

45

-1.2 -0.7 -0.2 0.3 0.8 1.3

E(V)

ip(

A)


100 mV/s

-28

-3

22

47

-0.8 -0.35 0.1 0.55 1

E(V)

ip(

A)


100 mV/s

0

70

0 320Time (sec)

Q(m

C)


84

0

2

4

6

8

0 2 4 6 8 10 12 14pH

i(A

)


0

300

600

900

1200

0 2 4 6 8 10 12 14pH

E(m

V)


-60

-30

0

30

60

90

-1 -0.5 0 0.5 1 1.5

E(V)

ip(

A)

Figure 4.42. Cyclic voltammogram of 350 g/mL Nifedipine on GCE at pH 1.0; scan rate

100 mV/s

85

0

5

10

15

20

25

0 100 200 300 400 500(mV/s)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


0

5

10

15

20

25

4 9 14 19 24

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

log

ip

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


86

0

300

600

900

1200

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

E(m

V)

pH 1.0 pH 4.0 pH 7.0 pH 9.2 pH 13.0


0

4

8

12

16

20

24

28

32

50 90 130 170 210

Conc(ppm)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


-30

-10

10

30

50

-1 -0.5 0 0.5 1 1.5

E(V)

ip(

A)


100 mV/s

87

-30

-10

10

30

50

70

-1 -0.5 0 0.5 1 1.5

E(V)

ip(

A)


100 mV/s

-30

-10

10

30

50

70

90

110

130

150

170

-1.2 -0.8 -0.4 0 0.4 0.8 1.2

E(V)

ip(

A)


100 mV/s

-30

20

70

120

170

220

270

320

370

-1 -0.5 0 0.5 1 1.5

E(V)

ip(

A)


100 mV/s

88

0

50

0 320Time(sec)

Q(m

C)


2

4

6

8

0 2 4 6 8 10 12 14pH

i(A

)


100

300

500

700

0 2 4 6 8 10 12 14pH

E(m

V)


89

-45

-35

-25

-15

-5

5

15

25

-1 -0.5 0 0.5 1

E(V)

ip(

A)

Figure 4.55. Cyclic voltammogram of 350 g/mL Nimodipine on GCE at pH 1.0; scan rate

100 mV/s

0

5

10

15

20

0 100 200 300 400 500(mV/s)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


0

5

10

15

20

4 9 14 19 24

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


90

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

log

ip

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


100

300

500

700

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

E(m

V)

pH 1.0 pH 4.0 pH 7.0 pH 9.2 pH 13.0


0

4

8

12

16

20

50 90 130 170 210 250 290

Conc(ppm)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


91

-45

-35

-25

-15

-5

5

15

25

-1 -0.5 0 0.5 1

E(V)

ip(

A)


100 mV/s

-45

-35

-25

-15

-5

5

15

25

-1.6 -1.1 -0.6 -0.1 0.4 0.9

E(V)

ip(

A)


100 mV/s

-45

-35

-25

-15

-5

5

15

25

-1.6 -1.1 -0.6 -0.1 0.4 0.9E(V)

ip(

A)


100 mV/s

92

-45

-35

-25

-15

-5

5

15

25

-1.2 -0.7 -0.2 0.3 0.8

E(V)

ip(

A)


100 mV/s

0

50

0 320

Time (sec)

Q(m

C)


400

600

800

1000

1200

0 2 4 6 8 10 12 14pH

E(m

V)


93

2

3

4

5

6

7

0 2 4 6 8 10 12 14pH

i(A

)


-60

-40

-20

0

20

40

60

-1 -0.5 0 0.5 1 1.5

E(V)

ip(

A)

Figure 4.68. Cyclic voltammogram of 360 g/mL Nitrendipine on GCE at pH 1.0; scan rate

100 mV/s

0

5

10

15

20

0 100 200 300 400 500(mV/s)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


94

0

5

10

15

20

4 9 14 19 24

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

log

ip

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


300

500

700

900

1100

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7

log

E(m

V)

pH 1.0 pH 4.0 pH 7.0 pH 9.2 pH 13.0


95

0

4

8

12

16

50 90 130 170 210 250

Conc(ppm)

ip(

A)

pH 1.0 pH 4.0

pH 7.0 pH 9.2

pH 13.0


-45

-35

-25

-15

-5

5

15

25

-1 -0.5 0 0.5 1 1.5

E(V)

ip(

A)


100 mV/s

-36

-27

-18

-9

0

9

18

-1 -0.45 0.1 0.65 1.2E(V)

ip(

A)


100 mV/s

96

-25

-20

-15

-10

-5

0

5

10

-1.2 -0.6 0 0.6 1.2

E(V)

ip(

A)


100 mV/s

-45

-35

-25

-15

-5

5

15

25

35

45

-1 -0.5 0 0.5 1

E(V)

ip(

A)


100 mV/s

0

50

0 320

Time (sec)

Q(m

C)


97

Table 4.1.Cyclic voltammetric data of Amlodipine on GCE at pH 1.0

(mV/s) Conc.

( g/mL) E(mV) i( A)

25

410

1024 3.41

50 1033 4.29

75 1045 4.79

100 1060 6.09

150 1062 6.31

200 1065 6.92

250 1036 6.27

300 1050 6.50

350 1054 6.45

400 1055 6.74

450 1051 6.84

500 1064 6.33

100

68 1045 4.79

117 1047 5.01

153 1051 5.33

182 1057 5.79

205 1060 6.09

223 1056 5.83

239 1053 5.81

98

Table 4.2.Cyclic voltammetric data of Amlodipine on GCE at pH 4.0 and 7.0

(mV/s) Conc.

( g/mL)

pH 4 pH 7

E(mV) i( A) E(mV) i( A)

25

410

882 1.18 743 1.44

50 905 1.52 758 1.40

75 922 1.50 767 1.43

100 914 1.99 796 3.24

150 939 2.07 798 3.20

200 949 2.17 805 2.36

250 960 2.2 812 2.37

300 961 2.21 808 2.45

350 975 2.27 815 2.50

400 982 2.30 816 2.98

450 983 2.35 845 3.12

500 984 2.43 904 1.82

100

68 978 0.725 744 0.98

117 933 1.050 753 1.72

153 934 1.55 769 2.05

182 922 1.79 780 3.00

205 914 1.99 769 3.24

223 917 1.98 790 2.35

239 920 2.01 777 2.30

99

Table 4.3. Cyclic voltammetric data of Amlodipine on GCE at pH 9.2 and pH 13.0

(mV/s) Conc.

( g/mL)

pH 9.2 pH 13.0


25

410

581 1.26 364 2.07

50 597 1.56 377 2.75

75 610 1.88 384 2.95

100 598 2.43 383 4.93

150 610 2.57 401 5.54

200 617 2.73 405 6.43

250 626 3.19 410 7.43

300 636 3.33 425 8.62

350 643 3.28 426 8.00

400 626 3.43 432 8.77

450 624 3.92 436 9.03

500 630 3.55 469 9.42

100

68 603 1.38 370 1.54

117 593 1.55 373 2.63

153 594 1.86 370 3.39

182 596 2.05 384 4.82

205 598 2.43 383 4.93

223 597 2.47 382 4.90

239 595 2.46 380 4.30

100

Table 4.4. Controlled potential coulometry of 2.5 x 10-7

M/dm3 AMLD

pH Electrolytic

Potential

Q (mC) No. of

electrons

1.0 968.5 51.32 2.15

4.0 703.0 49.19 2.21

7.0 609.8 53.88 1.99

9.2 573.0 50.66 2.10

13.0 413.0 48.20 2.00

101

Table 4.5. Cyclic voltammetric data of Felodipine on GCE at pH 1.0, 4.0, and 7.0

(mV/s) Conc.

( g/mL)

pH 1.0 pH 4.0 pH 7.0

E(mV) i( A) E(mV) i( A) E(mV) i( A)

25

380

1034 3.35 609 2.48 641 2.27

50 1038 3.52 618 2.56 656 2.34

75 1040 3.69 626 2.85 668 2.43

100 1044 4.82 641 4.74 694 3.02

150 1046 4.87 646 4.82 703 3.25

200 1050 4.97 654 4.80 711 3.36

250 1054 5.02 662 4.94 717 3.58

300 1059 5.42 667 5.16 730 3.69

350 1063 5.79 669 5.08 738 3.79

400 1067 5.92 671 5.33 741 3.69

450 1072 6.24 676 5.39 751 3.52

500 1076 6.79 678 5.54 763 3.56

100

63 980 3.05 644 0.55 685 1.66

109 1005 3.98 630 2.54 700 2.24

143 1015 4.28 643 3.71 684 2.69

169 1030 4.63 642 4.14 686 3.00

190 1044 4.82 641 4.74 694 3.02

207 1051 5.57 642 4.86 696 3.01

222 1057 6.99 640 4.99 695 3.07

102

Table 4.6. Cyclic voltammetric behaviour of Felodipine on GCE at pH 9.2 and pH 13.0

(mV/s) Conc.

( g/mL)

pH 9.2 pH 13.0


25

380

553 1.23 333 3.80

50 561 1.41 344 4.26

75 564 1.60 351 5.01

100 574 2.00 354 6.47

150 585 2.62 361 6.79

200 589 2.76 367 6.65

250 599 2.99 366 6.79

300 609 3.46 377 7.31

350 612 3.40 378 7.44

400 613 4.50 384 7.45

450 615 5.64 386 8.52

500 624 6.25 387 8.99

100

63 589 0.54 367 4.42

109 589 1.03 359 5.43

143 597 1.38 359 5.50

169 596 1.84 360 6.44

190 574 2.00 354 6.47

207 583 1.89 354 9.28

222 588 1.92 350 9.18

103


M/dm3 FELD

pH Electrolytic

Potential

Q (mC) No. of

electrons

1.0 831.7 95.08 2.19

4.0 770.8 85.96 1.98

7.0 740.0 86.40 1.99

9.2 666.0 95.96 2.21

13.0 458 96.58 2.01

104

Table 4.8. Cyclic Voltammetric data of Lercanidipine on GCE at pH 1.0

(mV/s) Conc.

( g/mL) E(mV) i( A)

25

610

557 1.52

50 568 2.12

75 572 2.42

100 586 2.98

150 598 3.67

200 608 4.47

250 622 5.02

300 635 5.71

350 638 6.28

400 642 6.85

450 652 7.48

500 668 8.17

100

111 549 0.18

124 552 1.97

229 554 3.56

271 558 4.40

305 559 5.72

333 557 6.10

356 560 6.70

105

Table 4.9. Cyclic Voltammetric data of Lercanidipine on GCE at pH 4.0 and pH 7.0

(mV/s) Conc.

( g/mL)

pH 4.0 pH 7.0


25

610

563 1.26 538 1.49

50 568 1.69 546 2.12

75 572 2.07 552 2.74

100 576 2.45 558 3.07

150 584 3.07 562 4.18

200 588 3.72 567 4.96

250 596 4.20 571 5.77

300 604 4.80 578 6.51

350 609 5.30 584 7.26

400 616 5.70 589 7.92

450 622 6.20 596 8.77

500 629 6.77 604 9.29

100

111 566 1.52 558 2.21

174 563 3.28 559 3.93

229 569 4.60 561 5.80

271 568 5.80 563 6.90

305 564 7.50 562 9.10

333 567 8.10 564 9.40

356 566 8.40 568 10.70

106

Table 4.10. Cyclic Voltammetric data of Lercanidipine on GCE at pH 9.2 and pH 13.0

(mV/s) Conc.

( g/mL)

pH 9.2 pH 13.0


25

610

527 0.83 367 12.95

50 524 1.23 370 13.72

75 512 2.63 369 14.67

100 519 2.69 353 16.58

150 512 2.99 378 16.70

200 538 3.01 381 16.99

250 541 3.12 389 17.02

300 547 3.13 391 17.37

350 549 3.15 395 17.87

400 555 3.33 399 17.96

450 557 3.37 413 18.13

500 559 2.14 425 18.27

100

111 564 2.88 357 15.10

174 548 8.88 358 16.20

229 524 7.96 318 17.45

271 524 7.80 342 17.65

305 529 8.21 353 16.58

333 521 8.11 355 16.85

356 519 8.10 361 17.01

107

Table 4.11. Controlled potential coulometry of 2.5 x 10

-7 M/dm

3 LERD

pH Electrolytic

Potential

Q (mC) No. of

electrons

1.0 683 48.10 1.99

4.0 677 45.34 1.88

7.0 637 51.14 2.12

9.2 607 48.70 2.01

13.0 452 52.31 2.21

108

Table 4.12. Cyclic voltammetric data of Nifedipine on GCE at pH 1.0, 4.0, and 7.0

(mV/s) Conc.

( g/mL)

pH 1.0 pH 4.0 pH 7.0


25

350

536 2.54 369 1.67 321 1.32

50 537 3.19 378 2.49 324 2.03

75 539 4.19 381 2.97 326 2.37

100 552 4.80 384 3.52 328 2.87

150 562 5.92 387 4.43 331 3.66

200 568 6.80 391 5.28 335 4.25

250 569 7.75 394 6.45 339 5.11

300 573 8.40 397 7.05 341 5.82

350 575 9.25 401 7.77 348 6.47

400 578 10.33 405 8.54 349 7.22

450 579 11.43 406 9.51 352 7.87

500 584 12.59 412 10.62 358 8.67

100

58 542 0.94 336 3.23 321 2.1

100 546 2.29 337 6.30 322 3.86

131 548 2.98 339 8.60 324 5.6

156 551 3.86 341 10.60 326 7.6

175 552 5.20 343 12.30 328 8.3

191 553 6.11 347 12.70 327 9.4

204 523 6.35 351 14.30 329 10

109

Table 4.13. Cyclic voltammetric data of Nifedipine on GCE at pH 9.2 and pH 13.0

(mV/s) Conc.

( g/mL)

pH 9.2 pH 13.0


25

350

370 2.52 204 2.19

50 372 3.67 383 5.97

75 388 4.33 154 5.99

100 394 5.12 202 15.51

150 395 6.17 203 16.333

200 397 7.27 207 17.76

250 401 8.32 209 18.18

300 402 9.37 212 19.79

350 403 10.62 215 20.01

400 403 11.84 217 21.41

450 404 12.67 219 25.23

500 407 13.87 221 27.17

100

58 474 0.59 198 4.67

100 412 1.36 205 18.79

131 392 1.47 204 19.91

156 404 1.51 202 21.51

175 394 1.55 203 25.51

191 412 1.71 204 27.81

204 417 1.92 205 29.10

110


M/dm3 NIFD

pH Electrolytic

Potential Q (mC)

No. of

electrons

1.0 398.0 61.13 1.98

4.0 185.0 64.53 2.09

7.0 140.0 58.36 1.89

9.2 210 57.14 1.99

13.0 243 52.34 2.04

111

Table 4.15. Cyclic voltammetric data of Nimodipine on GCE at pH 1.0, 4.0, and 7.0

(mV/s) Conc.

( g/mL)

pH 1.0 pH 4.0 pH 7.0


25

420

596 1.43 459 0.29 390 0.49

50 589 2.78 479 0.51 395 0.70

75 589 3.91 510 0.55 402 0.71

100 614 4.59 537 0.57 407 0.73

150 613 4.72 542 0.83 412 1.16

200 622 4.98 544 0.85 423 1.24

250 641 5.10 555 0.87 431 1.29

300 643 5.31 561 0.91 444 1.90

350 645 6.01 564 0.97 451 1.80

400 647 6.75 569 1.05 459 1.97

450 649 7.12 572 1.19 467 2.21

500 635 7.94 584 1.72 472 2.32

100

70 675 3.59 536 0.29 408 0.56

120 609 3.67 537 0.50 418 0.62

158 617 3.79 541 0.51 420 0.63

187 625 4.01 536 0.52 423 0.69

210 614 4.59 537 0.57 425 0.73

229 615 4.76 540 0.60 431 0.85

245 616 4.88 547 0.71 437 0.98

112

Table 4.16. Cyclic voltammetric data of Nimodipine on GCE at pH 9.2 and pH 13.0

(mV/s) Conc.

( g/mL)

pH 9.2 pH 13.0


25

420

247 0.83 103 6.39

50 282 0.91 156 7.41

75 281 0.97 181 10.72

100 282 1.03 129 12.08

150 333 1.22 179 12.79

200 335 1.42 205 13.01

250 337 1.51 203 13.67

300 339 1.52 238 14.32

350 341 1.53 263 14.79

400 347 1.55 241 15.79

450 355 1.57 254 16.898

500 383 1.61 314 18.99

100

70 307 0.67 278 9.015

120 308 0.80 277 10.12

158 308 0.86 279 10.85

187 307 0.89 279 11.35

210 282 1.03 279 11.95

229 309 1.42 270 12.31

245 311 1.57 271 12.61

113

Table 4.17 Controlled potential coulometry of 2.3 x 10-7

M/dm3 NIMD

pH Electrolytic

Potential

Q (mC) No. of

electrons

1.0 966.0 46.82 2.11

4.0 944.7 44.16 1.99

7.0 697.0 46.38 2.09

9.2 365 50.61 2.21

13.0 235 52.31 2.01

114

Table 4.18. Cyclic voltammetric data of Nitrendipine on GCE at pH 1.0, 4.0, and 7.0

(mV/s) Conc.

( g/mL)

pH 1.0 pH 4.0 pH 7.0


25

360

999 3.48 927 3.19 752 0.59

50 1010 3.86 930 4.51 762 1.11

75 1016 4.53 931 5.21 772 1.84

100 1031 8.69 932 6.62 782 1.98

150 1036 9.02 941 6.71 787 2.01

200 1043 9.77 947 6.77 792 2.11

250 1050 10.66 952 6.81 801 2.17

300 1050 11.84 963 6.03 830 2.19

350 1052 12.86 965 6.85 823 2.23

400 1059 13.60 972 7.01 826 2.47

450 1058 14.15 988 7.19 812 2.53

500 1059 14.57 992 7.69 817 2.61

100

60 1064 3.36 952 0.38 792 2.01

103 990 3.69 959 3.60 802 2.11

135 1004 6.64 963 5.07 804 2.34

160 1020 7.79 969 5.93 806 2.45

180 1031 8.69 932 6.62 808 2.59

196 1037 8.99 945 6.71 809 2.71

210 1041 9.02 957 6.96 811 2.83

115

Table 4.19. Cyclic voltammetric data of Nitrendipine on GCE at pH 9.2 and pH 13.0

(mV/s) Conc.

( g/mL)

pH 9.2 pH 13.0


25

360

610 1.64 408 4.59

50 617 2.11 421 6.79

75 621 3.01 422 8.81

100 626 3.48 436 11.86

150 629 3.57 439 12.29

200 631 3.69 442 13.75

250 637 4.01 451 14.01

300 639 4.79 456 14.52

350 642 4.81 462 14.75

400 647 5.62 471 15.01

450 652 6.79 483 15.12

500 657 8.39 499 15.68

100

60 615 3.07 471 5.71

103 621 3.34 478 6.72

135 623 3.37 479 7.69

160 625 3.41 465 9.81

180 626 3.48 476 11.86

196 627 3.51 478 11.91

210 629 3.53 471 11.99

116

Table 4.20. Controlled potential coulometric results of 4.75 x 10 -7

M NITR

pH Electrolytic

potential (mV) Charge (mC)

Number of

electron

transferred

1.0 924 49 2.070

4.0 856 55 2.200

7.0 740 45 2.982

9.2 733 51 2.113

13.0 590 46 2.004

Documents

CHAPTER - IV ELECTROCHEMICAL BEHAVIOUR OF CALCIUM …shodhganga.inflibnet.ac.in/bitstream/10603/8216/10/10_chapter 4.pdf · The cyclic voltammetric studies of AMLD was carried out