Informative Lecture about Atomic Absorption Spectrometer

3. Advantages and
Disadvantages of Atomic
Absorption
Spectrophotometer

4. Advantages of Atomic Absorption Spectrophotometer
 Easy to use
 Cheap
 Rapid
 Greater Sensitivity
 Efficient Atomization
 Even small quantities of the sample can be analyzed.
 Samples either in solid or solution form can be analyzed.

5.  Fails to detect non-metals.
 Simultaneous analysis of elements is not possible.
 Only able to detect 70 elements excluding earth metals.
Disadvantages of Atomic Absorption Spectrophotometer

6.  It is a phenomenon that leads to change in intensity of analyte signal in
spectroscopy.
 Interferences in AAS fall into two basic categories:
 Non- Spectral Interferences : Which affect the formation of analyte atoms.
1. Matrix interference
2. Chemical interference
3. Ionization interference
 Spectral interferences : High light absorption due to presence of absorbing
species.
1. Background correction
2. Continuum source Background correction
3. Others special interferences

7.  Non Spectral Interferences :
 1) Matrix Interference –
 When a sample is more viscous or has different surface
tension than the standard, it may result in difference in
sample uptake rate due to change in nebulization efficiency.
 Such interferences are minimized by matching the matrix
composition of standard and sample.

8.  2) Chemical Interference –
 If a sample contains a species which forms a thermally stable
compound with analyte that is not completely decomposed by
the flame energy than chemical interferences exists.
 Such interferences are minimized by using higher flame
temperature to provide higher dissociation energy.
 3) Ionization Interference –
 It is more common in hot flames.
 The dissociation process does not stop at formation of ground
state atoms.

9.  Excess energy of the flame lead to excitation of ground state
atoms to ionic state by loss of electrons.
 Ionization interference is eliminated by adding an excess of an
element which is easily get ionized.
 Spectral Interferences :
 Atomic spectral interferences are caused by presence of another
atomic absorption line or a molecular absorbance band close to
the spectral line of element of interest.
 Most of these interferences are due to molecular emission from
oxides of other elements in the sample.

10.  Background absorption :
 It extends over a broad wavelength band.
 It is referred to as molecular absorption.
 It is caused by light absorption due to vaporized solvents
droplets in flame.
 The absorption and scattering of radiation due to matrix
interferences give rise to sample background which becomes a
problem at wavelength below 350 nm.

11.  Continuum source Background correction –
 It is a technique for automatically measuring and for any
background component which might be present in an atomic
absorption measurement.
 The broad band continuum (‘White” light) source differs from
atomic line in that emits light over a broad spectrum of
wavelength.
 Other Spectral interferences –
 If the atomic absorption profile for an element overlap the
emission line of an other, a spectral interference is said to exist.

12. Sample Preparation for
Atomic Absorption
Spectrophotometer

13.  In an analytical method sample preparation is followed by a
separation and detection procedure.
 Only a few direct methods allow the introduction of the sample
without any preparation.
 In atomic spectroscopy the sample normally is found in one of
two forms: solid or liquid.
 The liquid phase seems to be the easiest form in which to handle
the sample, but some requirement for filtration is required.

14.  The selection of a sample preparation method is dependent
upon:
 (1) the analyte, (2) the analyte concentration level, (3) the
sample matrix, (4) the instrumental measurement technique,
and (5) the required sample size.
 A typical sample preparation procedure for solid and viscous
liquid samples involves digestion with a concentrated acid.
 e.g HNO3, HCl, or H2SO4. After dilution of the digested solutions,
samples can be directly injected into flame AAS as well as
graphite furnace AAS.
 Other sample preparation methods, including microwave and
high-pressure digestion, are also used to break up samples.

15. Sample preparation techniques Hot plate, microwave digestion, acid
digestion, high-pressure digestion
Acid HNO3, HCl, H2SO4, HF, H2O2
Contamination and Losses –
•The major problem in preparing samples for trace analysis is the
risk of contamination.
•Contamination is associated with several probable causes, i.e. the
grade of reagents used, sample storage container, steps of digestion
or dilution of the sample and their previous history, and human
intervention.
•Losses are a particularly significant problem in trace analysis.
Container surfaces, for example, may present a significantly large
area on which the analyte can be adsorbed.

16. Routine Maintenance for
Atomic Absorption
Spectrophotometer

17.  Instruments in good operating condition are a necessity in any
analytical laboratory .
 The four main areas of a program routine maintenance are
important :
 General instrument maintenance
 Gas supply maintenance
 Flame component maintenance
 Furnace component maintenance

18.  General Instrument Maintenance –
 Dust and condensed vapors can accumulate on the instrument
case, and corrosive liquids can be spilled on the instrument.
 To minimize damage, wipe off the instrument with a damp, soft
cloth using water or a mild detergent solution. DO NOT USE
ORGANIC SOLVENTS
 Gas Supply Maintenance –
 Acetylene is used as the fuel gas.
 Each gas is supplied to the instrument through piped supply
systems and rubber hoses.

19.  Acetylene should only be supplied through stainless steel or
black iron pipe.
 Check connections regularly between the supply and instrument
for leaks, especially when tanks are changed using a soap
solution or commercial leak detector.
 Check the rubber hoses connected to the instrument for fraying
and cracking.
 In addition, each time a tank is changed, check the regulators and
valves for proper operation.

20. Compressed Air Supply –
 Air may be supplied to the instrument from cylinders, a house air
system, or small compressor.
 Cylinders are the most expensive source of air, particularly where
large amounts are consumed and cylinders must be changed
frequently.
 If compressed air from an in-house supply is used, a regulator
assembly must be installed in the input line to the instrument.
 The air must be clean, dry and oil free.
 Approximately 50% of all gas unit failures are caused by moisture
or other impurities in the air supply.

21. Acetylene Supply –
 Acetylene is the only combustible gas.
 The gas must be supplied packed in acetone.
 Check the instrument operation manual for the correct delivery
pressure for the particular instrument being used.
 In addition, check the acetylene cylinder pressure daily, and
maintain in excess of 700 kPa (100 psi) to prevent acetone from
entering the gas line and degrading analytical results or causing
damage to the instrument.

22. Flame Component Maintenance –
 The flame component section of the instrument can be divided
into three areas - the nebulizer, spray chamber and burner.
Nebulizer -
 Place the nebulizer in an ultrasonic cleaner containing 0.5%
liquid soap solution for 5 to 10 minutes.
Spray Chamber –
 Discard the liquid in the liquid trap and wash both the spray
chamber and liquid trap thoroughly with laboratory detergent
and warm water. Rinse completely with distilled water and dry
all components. Refill the liquid trap and reassemble the spray
chamber.

23.  Burner –
 Each day after all analyses are completed, 50–100 mlof distilled
water should be aspirated to clean the nebulizer, spray chamber,
and burner.
 The burner should be removed weekly, scrubbed with a
laboratory detergent, and rinsed with distilled water.
 Furnace Component Maintenance –
 The graphite furnace accessory maintenance can be divided into
three major areas; the gas and water supplies, the work head,
and the auto sampler.

24.  Gas and Water Supplies-
 The regulated pressure should be 100–340 kPa (15–50 psi).
 At times the incorporation of air may be useful to fully ash a
sample.
 The water supply, used to cool the furnace, may be supplied
either from a laboratory tap or a cooling-recirculating pump.
 The water used must be clean and free of corrosive
contamination.

25.  Workhead –
 The workhead is a closed assembly with quartz windows on either end.
 Before starting an analysis, check the windows for dust or fingerprints.
 If needed, clean both sides of the quartz windows with a soft tissue
moistened with an alcohol/water solution.
 Autosampler –
 Regularly remove the rinse bottle for cleaning.
 This involves soaking the bottle in 20% HNO3 followed by rinsing with
distilled-deionized water.
 Refill the bottle with a solution of 0.01–0.05% HNO3 in distilled-
deionized water.

26. Troubleshooting for Atomic
Absorption
Spectrophotometer

27.  Troubleshooting for AAS –
 The AAS may not operate properly because of incorrect
operation.
 Following are some problems, which users may come across and
ways to solve them.
 1) the power supply indicator lamp does not light when the
power switch off AAS is switched on.
 2) No communication between AAS and Computer.
 3) Wavelength origin search error at initialization.

28.  4)The hollow cathode lamp does not light up.
 5)Line search failure.
 6)Hollow cathode lamp energy insufficient for line search.
 7)Flame can not be ignited.
 8)Air-Acetylene flame can not change to Nitrous oxide acetylene
flame.