CHAPTER - II

EXPERIMENTAL

Th~s chqpter deals wtth the purtficat~on ot mdtert?ls syntlles~s of

potassium benzyl xa~~thate and polnsslurn ~sobutyl xanlhate exper~rncntal

procedures used in the present ~nvesttgat~on and preparntlon of stock solut~ons

11 1 0 P~tr~ficnttun of M ~tcrtals

11 1 1 Double Dtshlled Waler

Deionised water was d~stllled twice The nlkaltne deion~sed water

was slowly distilled in an allpyrex vessel and collected middle fract~on The

purity 1s cl~ecked by conductivity

11 1 2 Punfieahon of Solvents

1 Acetone (SD s) was pur~fied uslng the procedure descr~bed by

~ramley'

2 Methyl ~sobutyl ketone2 (SD s) was pur~fied by disttllat~on

3 ~hlorofonn' (SD s) was purified by d~stilled at 61 C and stored m

mloured bottle

4 Carbon d~sulphide(SD s) was purified by fiacttonnlly disttlled

5 Carbon tetrachloride3 (SD s) was punfied by the distillate was

collected at 76 C

6 Petroleu~n ether (SD s) was purified over anhydrcus CaCll and

fractionated

7 7 Butanol and Bcnzyl alcohol (SD s) ~ l ~ s c solvents were dried

individually with anhydrous calaum sulphate and fr?ct~on?lly d~stllled

dt 90 C and 205 C rcspccllvcly

8 Ethyl acetate (SD s) A mixture of ethyl acetate acetic anhydride and

sinall quantities of sulphuric acld were reflux and then fractionated

The d~stillate was sliaken wit11 anhydrous potassluln carbonate filtered

and redistilled

9 D~thlzone Standard d~th~zone solution was prepared by usmg Merck

G R grade dithlzone without further purification

10 rhiocyanateB 8 5 g of ammonlum th~ocyanate is dissolved in 1000 in1

water (0 1M) Thc solution IS standard~zed w~th 0 IM sllver mtrate

solutlon

11 2 0 Synthcs~s of Reagents

I1 2 1 Potasslum Isabutyl Xanthnte

Thls was prepared accord~ng to the procedure glven by ~ o g e l '

18 g of potassium hydrox~de pellets and 100 g (123 5 ml) of dry lsobutyl

alcohol were taken m a round bottom flask and refluxed for one hour The

liquid was decanted from res~dual sol~d into another dry flask and allowed to

cool To this 36 g (28 5 mi) of carbon disulph~de wos added slowly wh~le

thc contcnh were constantly st~rred rhe result~ng product wns t~ltcred after

cooling in ice The purlly was determined by measuring the meltlng poiid

11 2 2 1 otasslum Beuzyl Xauthste

The reagent potasslum benzyl xanthate was prepdred by the

method suggested by Fostor e l a1

To 26 ml of benzyl alcohol 14 g ot potasslum hydroxldc solutlon

was added dnd the same was taken Into a con~cnl flask r h ~ redction

lemperature was marnta~ned below 20 C 15 ml of arbon disulphide was

added gradually and the mlxture was slmultnneously stirred usmg a mechanical

stnrer for about twenty lninutes On the gradual add~tion of carbon d ~ s ~ ~ l p ~ d e to

this so1ut1011 a thick redd~sh brown mass was formed whrch was separated by

gentle suctton The left over solid after sucuon was dissolved In a few ml of

pure acetone The Impure polysulphldes form two separate layers red and

yellow By means of a separatory funnel only the yellow layer was taken To

th~s petroleum ether was added to obtain a fine faint yellow sol~d of potasslum

benzyl xanthate It was filtered out washed wtth petroleum ether and dned In a

vacuum desiccator The proccss ot rccryslall~sdt~on was rcpe~ted twicc. Lor

Icquiring n h~gh purlty (I 80 C - 182 C)

11 3 0 Prcparnt~on of StockSolut~onv

11 3 1 Iron Solution (1 mg/ml)

0 726 g of ferr~c chlonde was d~ssolved 111 double d~st~lled water

0 25 ml of con~e~ltmted hydrochlortc ac~d was added and the solut~on la dlluted

in a volumetr~c flask to 250 ml

I1 3 2 Copper Solut~on (I rnglrnl)

0 670 g of cupric chlor~de was dissolved In deionlsed double

dlhtllled water containing 0 25 ml of concentrated hydrochlor~c ac~d and the

solut~on was made upto 250 ml volumetric flask

I1 3 3 Lead Solution (1 mglml)

0 3995 g of lead nltrate was d~ssolved In double d~stilled water

0 25 ml of concentrated nltrlc ac~d was added and the solution drluted in a 250

ml volumetr~c flask

11 3 4 Cobslt Solut~on (1 n~&lml)

1 0093 g ot cob?ltous chlor~de was d~ssolved m double distilled

wat r containing 0 25 ml of concentrated hydrochloric acid and the solution

diluted in a 250 ml volumetr~c flask

11 3 5 Cl~roniiu~n Solutio~i (I mg/ml)

0 7075 got potasslum dtchromate was dissolved lo double d~stllled

wntor and made upto 250 ml

I1 3 G D~vcrse Ion Soluttons

Interference anions and cattons are prepared according to the

procedure given In the Standard books

11 4 0 Pteparnt~on of Buffcr Soluttons

I1 4 1 IIydrochlortc Ae~d - Potaatum Cl~lortdc Buffer

0 2 M of hydrochloric oc~d and potasslum chlor~de solut~ons were

prepared and m~xed in su~table proportion to get the pH 2 and 3

I1 4 2 Acetrc Acid Sodlurn Acetate Buffer

0 2M of acet~c ocrd and sodium acetate solut~o~is were prepared are

mixed in a su~table proportion to get the pH from 4 0 to 7 0

11 4 3 Ammon~um Chlorrde - A~nmon~um Hydroxtde Buffer

0 2M of amrnonlum chloride and ammonlum hydrox~de solut~ons

were prepared and mxed m su~tabIe proportions to obta~n the pH from 8 to 12

11 4 U collect lot^ o f W a t ~ r Sun~ples

Water samples were collected Cram Mlnduslan Zlnc I t m ~ t ~ d

V~gakhapntnam (Industrial effluents) and in and nround Chlrala town

Praknsaln D~st Andhrn Prndesh Ind~a (ground water samples) In polyethylene

bottles leached w~th nltrlc ac~d All the sample bottles must be rlnsed 2 or 3

t~mes w~th the l ~ q u ~ d to be collected before fill~ng w~th the final sample To

destroy the orgun~c matter the wnste water samples were treated w~tll a tnlxture

of n~trtc actd and perchlor~c actd

I1 G 0 Pharmaeeut~cal Sampl~ng

The samples were treated separately w~th concentrated nitric actd

on a hot plGte at a low temperature to avo~d v~ole~lt spurtlng The res~due ot

each sample was collected and agatn nltnc ac~d was added The temperature of

the hot plate was rncreased to 300 C The residue obta~ned was dissolved m

nltrlc ac~d ( I I) and then slowly headed for two hours to procure a dry mass

Flnally the mldue was dtssolved m a mintmum amounts of double d~sttlled

water The same solut~on was qunnt~tntlvely transferred ~ n t o a 50 ml volumet~c

flask and then made upto the mark with double dlst~lled water

11 7 0 Sarnplrl~g of Maler~ala

11 7 1 Dry Ashtog ~ r o c e d u r c ~

Tal\e h o w qunntily of d n d powdered sample mnlerldl In a

porc~ldin or sillca basin ignite at 500 550 C for at least 2 liours or Inore in n

muffle furnace A h r ashing IS ovcr cool and add 5 ml of l I HCI Cover by

wakh glass and h ~ n t at low tempLrature for about 15 mlnuks Add 1 ml nitrlc

dc~d and evaporate to dryness cont~nue heating for furthcr one hour to

dehydrate silica Now add 1 0 ml of 1 I HCi swirl to dissolve the residue add

some water and warm for complete drssolution Filter through a Whatman No

44 filter paper and make up a final volume to 100 ml in a volumetr~c flask after

several washings of filter paper by portions of water

11 7 2 Wet D~gestion ~ r o c e d u r e ~

Take hown quanbty of dried and gmund plant mtenal ~nto a 100

in1 Kjeldnhal flask Add I 0 In1 of 60/ HCI04 5 in1 HNO, and 0 5 ml HzSOJ

Heat at low temperature Increase the heat and digest for 10 15 minutes after

appearnnce of whlte fumes cool filter and make up the find volume ta 100 ml

after several washings of filter pper by small portions of water

I1 8 0 Instrumcob used in theprcscnt Invest~gt~on

I A double beam atom~c absorphon spectrometer (Perhn Elmer 3100)

equ~pped with a hallow cathode lamp of Cu Co Cr and Pb

2 A double beam spectrophotometcr PR I Sh~madzu UV 240 w~th 10

mrn glass cells

3 D~gitnl pH meter (El~co LI 120)

I1 3 U Cxpernncntul Pru~cdures Used in the I resent I m c u t ~ ~ u t ~ o n s

11 9 1 R I I I ~ ~ O I I I Plot

~rves"' stated that a sbcght hnt obtac\~ed in Beer s law d m not

show d~rectly the concentratlon range w~thin whlch accurate determ~nat~on of

the coloured specles 1s poss~ble The optrinuln range for h~ghest precision IS

determrned by plotttng absorbance (1 transm~ttance) against the log of metal

Ion concentration in &ml In th~s graph a s~gmo~d shape curve" IS obto~ned

wh~ch shows the ophmum range for accurate determmahon of the metal Ion

When a system obeys Beer s law

Adc 230 -= Ap AplAlobo

AplA log c rs the slope of the R~ngbom plot, hence

Ac 230 100-=-

0 slope

absorbance IS oalculatod from the equatlon

absorbance = l -kansmrttance

the relat~on between absorbance and transrnlttance is gven by A = log T

A plot of ~ l a l v e error in concenlritlon versus percentage

transmlttance ~ndlcates that the error is inlnlmum and fairly eonstnnt over 70 -

60 / of t~msm~ttance values or 80 - 40/ absorban~e valu~s (or 0 2 - 0 7

absorbance values in tenns of Beer s law) The two outstand~ng advantages of

Ringboin plot are

1 At a blance it represenls the con~entratlon range in which Lhs error In Lhb

analysis is ininlmum (th~s corresponds to the nearly llilenr portlon of the

plot) and

2 In any concentration range the accuracy of the analysis can easily be

evaluated

11 9 2 Molar Ratro Method

Th~s method was proposed by Yoe and ones" for investigation of

coloured complexes m soluhon In thls melhod a senes of soluhons are

prepared n wh~ch the analytical mncentratlon of the metal ion is kept constan4

while that of the reagent is var~ed The absorbance of the solution is measured

at a su~table wavelength and plotted against the ratto of the moles of reagent

(vanes) to moles of the metal Ion (fixed) If only one stable coinplex is formed

whrch has selechve absorpt~on then the abgorbnce Increases approx~mately

linearly w~th the mole rat10 then becomes constant The absc~ssa of the po~nt

of Inter section of the two tailgents gives the colnblning rdtio of h e metal to

l~gand

11 9 3 Job s Method of Coot~nuou~ Var~at~on

Though the prrnc~ple of contlnuous varlatlon was first appl~ed by

~rstromaslensky" and D ~ V I ~ I ~ I I " the discovery of the method is frequently

attr~buted to ~ob" who applied it to complex systems and it was modified by

Vosburgh and cooper16 in the method of contlnuous vanatlons metal and

llgand solut~ons w~th ~dentlcal analytical concentrations nre mixed in such a

way that the total volulne and total moles of reactants in each mixture 1s

constant but the mole ratlo of reactants vanes systemat~cally The absorbance

of each solution 1s then measured at su~table wavelengths Its absorbance is

then plotted against the volume fract~on of reactant that is V f l ~ + VL where

V" 1s volume of the metal solution and VL is the volume of llgand A

maximum absorbance occurs at a volume ratlo V f l ~ corresponding to the

combining ratlo of metal to l~gand m the complex which suggests the

composltlon of the formula as ML3(

IL9 4 Asmus Method

The mod~fied form of Job s method gives accurate results only

when the complex IS hlghly stable In the case of we& complexes an mverted

parabolic curve w~ll be obtalned rather than two perfect straight lines

Intersecting at a single point mtmducing unccrtainity in the dekenninatim of

the composition of the complex The uncertamity has been tound greater with

I 2 and 1 3 complexes than 1 I complexes (metal l~ymd) In such coses

extrapolatlo11 techii~que of the linear portlons 1s not suggestive Even the molar

ratlo method of Yoe and Jones glves lnaccurnte conclus~ons regnrding the

lormula of wedk complexes Ilence ~smnus~' suggested yet another method

for the determmat~on of the camposltion of complexes Even though it is

s~mllar in the experimental part to that of the earlier methods described it IS

d~fferent in terms of evaluation

In this method keeping the total volume of the solut~on (V)

constant the absorbance values of solutions containing fixed volume of the

metol ton solution (V ) of concentrat~on (a) and lncreaslng volumes (V) of the

l~gand solut~ons of concentrahon (b) are measured From the absorbance the

extinctloll modules m IS calculated by div~ding the absorbance by the cell

width Graphs can be drawn between l/m and IN where V is 1 ml 2 ml and

so on The value of n correspondmg to the l~near graph Vves the number of

llgands attached to the metal ion

11 9 5 Edmonds and Birnbaum s Mcthod

The stability constant of a metal complex (hCJ IS calculated by

Edrnonds and Birnbaum s method In thu method different al~quots containing

u m c concentrdltotls of tnetdl Ion are takcn To t11es.c varylns concentrdllons of

reagent solut~ons wtth proportional mcrease are added t~ll the lnetnl to llgand

ratio 1s reached The stabll~ty on st ant of the complex 1s ~alcula t~d by

substttut~ng the measured values of absorbance in the tonnula appl~cablc to a

complex of known composltlon Thus m th~s method it IS necessmy to know

the formula of the complex for cnlculatlng the lnalrlbtl~ty constant The general

formula a represented as

b d (log 1, - log 1J Instab~ltty constant = - - - - -

(d log l - b log I,)

Where b and d are the concentrations of the reagent In two

successive solutions of x and y respechvely Of these b and d b IS Iesser

and d 18 h~gher in concentrahon n IS the number of moles of reagent per

mole of metal Ion log 1 and log 1, are the opt~cal dens~t~es of solut~ons x and y

respechvely

Based an the well establ~shed and proper methods of determlnat~on

of metal Ions varrous food samples pharmaceutical samples end ~ndustnal

effluents have been mnveshgated m the chapters to follow

I A Bromely J Chein Soc 10 (1916)

2 A Wclssberger E S Prosknher J A Red~ck and E E Toops i r

Organ~c solvents lntcrsc~ence Publ~shers Inc New York (I 9sS)

3 A I Vogel A text book of pract~cal Organ~c Chemistry 'i ed

Longmanns Green and Co Ltd London (1966)

4 A 1 Vogel A text book of pract~cnl organic chemlsby (Longmann

London) 3 %d (1 968 and 1969)

5 L S foster Utnn Eng Expt S h Tech (1969)

6 S Irw~n Shupe J Assoc Official Agr~ Che~n 25 495 (1942)

7 A l Vogel A text book of Quant~tat~ve Inorgan~c Analys~s

(Longmann) 3 h ((1961)

8 Vogel s Text book of M~cro and Sem~m~cro Qual~htlve lnorgan~c

Analygs Reveed by Svehla G (Longmams) 5' ed (1979)

9 R K Trivedy and P K Goel A text book of p m h l methods ~n ecology

and env~mnmental sciences Environmental Publlcatlons KARAD pp

140 141 (1987)

10 G H Aryes Anal Chem 21 652 (1949)

I I A Z kngbom Anal Chem 1 15 332 (1939)

12 J H Yoe and A L Jones Ind Eng Chem Anal Ed 16 1 I1 (1944)

13 Ostmm~sslensky J Ber 44 268 (191 1)

14 R D Denlson, Trans Faraday Soc 8 20 (1912)

15 P Job Ann Chlm 9 133 (1928)

16 W C Vmburgh and G R Cooper J Am Che~n Soc 63 437 (1941)

17 E Asmus Z Anal Chem 178 104(1960)