Atomic Absorption Spectrometry: Principles and Applications, Study notes of Chemistry

Download Atomic Absorption Spectrometry: Principles and Applications and more Study notes Chemistry in PDF only on Docsity!

Chapter 9: Atomic Absorption Spectrometry

Chapter 9: Atomic Absorption Spectrometry

Read: pp. 230 – 249

Problems: 9-1,3,5,6,

Figure 9-13a

A(

λ

ε

λ

)bC = log P

o

/P

Flame

Flame

Burner

Burner

In AAS, the flame functions as (i) sample holder, (ii) desolvation source, and (iii) volatilization source.

Figure 9-

Flame Structure

Flame Structure

Primary zone: C

2

, CH, and other

radical emission Secondary zone: oxygen present sostable molecular oxidesare formed for somemetals Interzonal regions: hot region, most widelyused for analysis

Figure 9-

h

ν

Optimum analysis position in the flame depends on theparticular element and its chemistry:

Figure 9-

Desired line of source is selected with monochromator:

Figure 9-

Monochromator

Monochromator

Wavelength Separator

Wavelength Separator

Figure 7-

n

λ

= d(sin i + sin r)

R =

λ

/

∆λ

= nN

N = grooves/mm

Properties: light gathering power, stray light rejection,

resolution, and linear dispersion

Single Single

Beam Spectrometer: Beam Spectrometer:

Figure 9-13a

Double Double

Beam Spectrometer: Beam Spectrometer:

Figure 9-13b

Typical Figures of Merit for AAS

Typical Figures of Merit for AAS

Detection limits: ng/mL (ppb) for flame

pg/mL (ppt) for electrothermal

Linear range: 10

3

4

for flame

2

for electrothermal

Precision: 1 – 2% RSD for flame

5 – 10% RSD for electrothermal

Accuracy: 1 –

2% for flame

% for flame

Remember: mg/L = ppm

ug/L = ppb

ng/L = ppt

Chemical Problem

Chemical Problem

Typical data for the determinationof lead (Pb

2+

) by graphite furnace

AAS in standards was 0.05 μ

g/mL (0.09 AU), 0.

μ

g/mL

(0.16 AU), 0.

μ

g/mL (0.31 AU)

and in a sample of cannedorange juice was 0.10 AU. Assume that these absorbancedata were obtained for 2

μ

L

aliquots of standards andsample. Calculate theconcentration of lead in theorange juice sample.

Figure 9-

Calibration equation: A = 1.4714 C + 0.015Orange juice sample: A = 0.

• μ = − = − =

2

Pb

mL

/

g

058

.

0

4714

.

1

015

.

0

10

.

0

4714

.

1

015

.

0

A

C

Spectral and Chemical Interferences

Spectral and Chemical Interferences

Remember: Goal is neutral atoms in the gas phase! Remember: Goal is neutral atoms in the gas phase!

Absorption or emission of an interfering species overlaps orlies so close to the analyte absorption or emission thatresolution is not possible.

Rare with HCLs.

Presence of combustion products that exhibit broadbandabsorption or particulates that scatter radiation. Both diminishpower of transmitted beam and lead to positive errors.

If caused by fuel/oxidant mixture, then correction is possible

by running a blank and performing background subtraction.

More troublesome problem when absorption or scattering

results from the sample matrix.

Terms to Know!!!

ablation chemical interference matrix

aerosol detection limit nebulization

atomic absorption Doppler effect releasing agent

atomic emission graphite furnace self-absorption

atomic fluorescence hollow cathode lamp spectral interference

atomization ionization interference ionization suppressor

background correction

Boltzman distribution