Expt 6 AAS Presentation

8/4/2019 Expt 6 AAS Presentation

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Experiment 6:

Determination of TraceLevels of Copper inVegetable Samples Using

the Atomic AbsorptionSpectrophotometerArgamino.Buenaseda.Gajigan

Chem 127.1 Maam Cruz


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INTRODUCTION


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AAS

one of the mostcommoninstrumental

methods foranalyzing formetals and somemetalloids


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PARTS


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Hollow Cathode Lamp

Provide the analytical light line for theelement of interest

Provide a constant yet intense beam ofthat analytical line


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Nebulizer

Suck up liquid sample at a controlledrate

Create a fine aerosol for introductioninto the flame

Mix the aerosol and fuel and oxidant

thoroughly for introduction into theflame


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Flame

Destroy any analyte ions and

breakdown complexes Create atoms (the elemental form) of

the element of interest


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Monochromator Isolate analytical lines' photons passing

through the flame

Remove scattered light of otherwavelengths from the flame

In doing this, only a narrow spectral line

impinges on the PMT.


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Photomultiplier Tube (PMT)

As the detector, the PMT determinesthe intensity of photons of the analytical

line exiting the monochromator.


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KANGKONG

Ipomoea aquatica

A smooth, widely spreading vine,

with the stems trailing on mud orfloating on water.


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KAMOTE Ipomoea batatas

A herbaceous vine with alternateheart-shaped or palmately lobedleaves and sympetalous flowers.

The edible root is long and taperedwith a smooth skin of varying colorsfrom red, purple, brown and white.


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Copper Content Standards

Kangkong

37.68 mg/kg (dry weight) (Wang, 2010)

3.34-3.95 mg/100g (Umar, 2007) Kamote

0 mg/100g (Antia, 2006)

Root: 0.34 mg/100g (www.whfoods.org)


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METHODOLOGY


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Preparation of StockSolutions

0.5 g of coppermetal weredissolved in 20 mL

of 1:1 nitric acid diluted to mark in

250-mL volumetricflasks

5 mL aliquot wereobtained from theprepared solution

diluted to a 100-mL


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Preparation of Standard

Five clean, 50-mLvolumetric flaskswere prepared and

labeled withnumbers 1 to 5.

0.50, 1.25, 2.50,5.00 mL of the

stock solution wereplaced to flasks 1,2, 3, and 4respectively

to re are 1.00,


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Preparation of Sample

The leaves fromthe vegetablesamples were

rinsed and dried inthe oven

The temperature ofthe oven was

maintained at 100to 150C for 45minutes.

Two (2) grams of

the dried sample


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Preparation of Sample

The mixture wasboiled slowly atlow setting for 20

minutes. 10 mL distilled

water was addedto the cooled set-

up.

It was thenfiltered to a 50-

mL volumetric


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Analysis of theVegetable Sample

The absorbanceof the standardsolutions and the

sample weremeasured usingthe requiredinstrumental

parameters (forCu) of the atomicabsorptionspectrophotomet

er.


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Standard AdditionMethod

Five clean 50-mLvolumetric flaskswere prepared and

labeled withnumbers 1 to 5.

To each flask,10 mLof the digested

sample were added.

0.00, 0.50, 1.25,2.50, 5.00 mL of the

stock copper


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Standard AdditionMethod

The absorbancesof the solutions

were measuredusing the requiredinstrumentalparameters for

Cu.


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RESULTS


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DIRECT CALIBRATION

StandardConcentration

(ppm)Absorbance

CorrectedAbsorbance

Blank 0.00 0.0123 0

1 1.00 0.1937 0.1814

2 2.50 0.3685 0.3562

3 5.00 0.6789 0.6666

4 10.00 1.1751 1.1628

0 2 4 6 8 10 12

0

2

4

6

8

10

12f(x) = 1.#NANxR = 1.#NAN

Concentration (ppm)

Corrected Absorbance

Kangkong 0.036 = 0.1089

[Cu] + 0.088

[Cu] = -0.4775ppm

Accounting for

dilution:


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STANDARD ADDITIONMETHOD

Kangkong

Set-upVolume ofStandard

(mL)

Absorbance

Trial 1 Trial 1 Trial 3

1 0.00 0.0119 0.0127 0.01332 0.50 0.1619 0.1632 0.16123 1.25 0.3350 0.3311 0.32824 2.50 0.6165 0.6147 0.61485 5.00 1.0855 1.0820 1.0820

Set-up

A/Ao

(Vx+Vs/Cs)

(A/Ao) (Vx +Vs/Cs)

Trial 1 Trial 1 Trial 3 Trial 1 Trial 1 Trial 3

1 0 0 0 0 0 0 02 14 13 12 0.105 1.4285 1.3493 1.27263 28 26 25 0.1125 3.1670 2.9330 2.77614 52 48 46 0.125 6.4758 6.0502 5.77825 91 85 81 0.15 13.683 12.780 12.203

A/Ao= 0.1619/0.0119

=14

(Vx +Vs)/Cs=(10+0.50)/100= 0.105

(A/Ao )(Vx+Vs)/Cs= 14 X 0.105= 1.4285


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Kangkong

0 2 4 6 8 10 12

0

2

4

6

8

10

12f(x) = 1.#NANxR = 1.#NANf(x) = 1.#NANxR = 1.#NANf(x) = 1.#NANxR = 1.#NAN

LinearRegressionfor

LinearRegressionfor

LinearRegressionfor

Volume of Standard (mL)

(A/Ao) (Vx +Vs/Cs)

Cx = (1/m)Linear Equations:

y = 2.7261x + 0.0018Cx=0.3668y = 2.5459x + 0.0019Cx=0.3928y = 2.4333x + 0.0021Cx=0.4110

Average of Cx = 0.3902ppmAccounting for dilution:(0.3902mg/L)(50mL/10mL)

(50mL)(1L/1000mL)/2g= 0.0488 mg/g



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Kamote

Set-upVolume ofSolution

(mL)

Absorbance

Trial 1 Trial 1 Trial 3

1 0.00 0.0272 0.0261 0.02762 0.50 0.1696 0.1679 0.17333 1.25 0.3308 0.3315 0.33174 2.50 0.6200 0.6191 0.62025 5.00 1.1073 1.1078 1.1088

Set-up

A/Ao(Vx

+Vs/Cs)

(A/Ao) (Vx +Vs/Cs)

Trial 1 Trial 1 Trial 3 Trial 1 Trial 1 Trial 31 0 0 0 0 0 0 0

2 6 6 60.105 0.6547 0.6755 0.6593

3 12 13 120.113 1.3682 1.4289 1.3520

4 23 24 22 0.125 2.8493 2.9650 2.8089

A/Ao= 0.1696/ 0.027=6

(Vx +Vs)/Cs= (10+0.50)/100= 0.105

(A/Ao )(Vx +Vs)/

= 6 X 0.105= 0.6547



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Kamote

0 2 4 6 8 10 12

0

2

4

6

8

10

12f(x) = 1.#NANxR = 1.#NANf(x) = 1.#NANxR = 1.#NANf(x) = 1.#NANxR = 1.#NAN

LinearRegressionfor

LinearRegressionfor

LinearRegressionfor

Volume of Standard (Vs)

(A/Ao) (Vx +Vs/Cs)

Cx = (1/m)Linear Equations:

y = 1.2152x + 0.0524Cx=0.8229y = 1.2673x + 0.0573Cx=0.7891y = 1.1979x + 0.0469Cx=0.8348

Average of Cx = 0.8156 ppm

Accounting for dilution:(0.8156mg/L)(50mL/10mL)(50mL)

(1L/1000mL)/2g= 0.1019 mg/g



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discussion


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Atomic AbsorptionSpectrophotometry

AAS Simple, low cost

Application: effective determination of

trace amounts of heavy metals inbiological samples


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Atomic AbsorptionSpectrophotometry

Cathodelamp

made ofmetal underinvestigation

emit the line

spectrumcharacteristic of theparticularelement


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Sample Preparation

Air dried

Advantage: ease of homogenization

[Cu] reported per dry mass Rinsed

remove surface contaminants

Oven dried Further drying


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Sample Preparation

Solid samples should be brought intosolution

acid attack

alkali fusion and subsequent acid attack

dissolution in solvent

Acid attack important not to add components that

interfere with the copper determination

nitric acid causes no interference in the


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Direct Calibration Method

Plot the measured absorbanceagainst the concentration of thestandard solution (ppm)

copper atoms in the flame

follow the Beers Lambert Equation

A = bc


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Direct Calibration Method

Blank determination exhibits little absorbance

distilled water used as blank contains

traces of copper ions

Standard Solution

copper metal

high purity: minimize chemicalinterference effects due to chemicalimpurities present in some inorganic

salts available in the laboratory


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Standard Addition Method

Absorbance of several solutionscontaining a constant volume ofdigested kangkong and kamote

sample and varying volume ofstandard copper solution wasmeasure

Derivation:


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Standard Addition Method

Standard Addition

accounts for the matrix effects

used when sample matrix affects theresponse of the analyte.

usually necessary for complicatedsamples such as leaves

some components in the leaves canaffect the response of the copper


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Interference

Spectral Interference

presence of very few atoms

Interference from flame emissions whichcan be reduced by modulating lamp

Interference from molecular speciesabsorbing lamp photons that occurs at

shorter wavelengths which can beremoved by using a deuterium lampwhich has a broader band light source.


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InterferenceChemical Interference Solution

Matrix effect standard addition method

Poor nebulization because ofhigh viscosity

Use hotter flames

Poor volatility Use hotter flames

Formation of metal oxides andhydroxides

Using fuel rich flame

Ionization of analyte atoms Add an ion that has a lowerionization potential

Light scattering by particles inthe flame

Background correction ORSelecting the optimum temperaturewhere the background signal andanalyte can be effectivelyseparated ORUsing broad band light source (i.e.

deuterium)


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Interference

Other methods in overcoming someinterference

using higher temperature flame such as

nitrous oxide which sufficiently causecomplete dissociation of some refractorycompounds

extracting the analyte element extracting the interferent

use of releasing agents that will

combine with the interferents.

I t f i C


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Interference in Cudetermination

High Zn/Cu ratio which lowers theobserve absorption.

Some papers suggest the use of nitrous

oxide can lessen the interference.


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Possible Sources of Errors

Low concentration of standardssolutions

solns deteriorate due to the absorption

of the analyte in the walls of thecontainer

Oxide coating of the metal standard

(Cu metal) was not properly removed Differences in the amount of sample

and standard that reach the flame

because of the differences in the


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CONCLUSION


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CONCLUSION

Trace amounts of severalnutritionally important elements invegetable samples could be

successfully determined throughAtomic AbsorptionSpectrophotometry.

The analyte concentration wasdetermined from the absorption ofits solution using the Beer-Lambert

equation.


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CONCLUSION

In the experiment, two methods wereused to determine the copperconcentration in leaf samples: direct

calibration method and the standardaddition method.

In direct calibration method, the

equation y = 0.1089x + 0.088 wasobtained as standard curve. Thecalculated concentrations of Copperwere -0.0112 mg/g and 4.76E-3 mg/g for

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Expt 6 AAS Presentation