Principle of Atomic Absorption Spectrophotometry

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Principle of Atomic Absorption Spectrophotometry
Mr. Charnchai Suracheep
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Introduction

• Atomic Absorption Spectrophotometry,
• which are standard instruments for
• the determination of metal elements,
• are widely applied of samples, such as
• agriculture chemical, clinical and
• biochemistry, minerals, food and
• drugs, environmental and other.

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Principle of Atomic Absorption Spectrophotometer
Principle of the Atomic Absorption
Method Atomized elements each absorb energy of a
wavelength that is peculiar to that element. The
atomic absorption method uses as its light source
a hollow cathode lamp which emits light of a
wavelength that is peculiar to each element.
Elements within a solution are heated in a flame
or electrically (2000K to 3000K) and subsequently
determined using the fact that the degree of
absorption will vary with its concentration.
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Principle of Atomic Absorption Spectrophotometer
Atomic Absorption Spectroscopy, AAS
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Sodium (Na) energy states
Electronic Transition
Excited state (II) 3.6 eV
Excited state (I) 2.2 eV
330.3 nm
589.0 nm
Ground state 0.0 eV
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Relation between light absorption and density

• When light of a certain intensity is given to
  many atom in ground state, part of this light is
  absorbed by atoms.

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Lambert-beers Law
Relation between light absorption and density
I I0 e-k .l .C
Abs -logI/I0 k .l. C
k proportional constant l path length C
density (concentration)
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Calibration curve
Relation between light absorption and density

• Graph show the relation between absorbance and
  concentration

Absorbance
Concentration (ppm)
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Atomization method

• Atomic absorption spectrometry measures
  absorption of free atom.
• Free atom means an atom not combined with other
  atoms.
• Elements in the sample to be analyzed are not in
  the free state, and are combined with other
  elements invariably to make a so-called molecule.

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Atomization method

• The combination must be cut off by some means to
  free the atoms.
• This is called atomization
• 2 types
• - Flame method
• - Flameless method

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Flame Method
With the Flame Method, the sample solution is
converted into mist-form using a nebulizer, and
then introduced into the flame. It is atomized by
the temperature of the flame. Measurement time
A few dozen seconds
Flame Atomization Method
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• Optical diagram of Flame Atomic Absorption
  Spectrometers

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Flame selection
Flame Method

• These flames vary in temperature, reducibility
  and transmission characteristics.
• Selected according to the element being analyzed,
  and properties of the sample.

• Argon-hydrogen Max. temp. 1,577 0C

• Air-hydrogen Max. temp. 2,045 0C

• Air-acetylene Max. temp. 2,300 0C

• Nitrous oxide-acetylene Max. temp. 2,955 0C
• (For elements are hard to combine with oxygen
  (Al, Si, V, Ti, etc.))

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Flame Method
Flame selection
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Flameless Method (Graphite Furnace)
Graphite tube
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Flameless Method (Graphite Furnace)

• Sample is injected in the formed graphite tube.
• An electric current of 300 ampere (maximum) is
  applied to the tube.

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Flameless Method (Graphite Furnace)

• In an actual measurement heating is done in 3
  stage.

- Drying stage (100oC)
- Ashing stage (400-1000oC)
- Atomizing stage (1400-3000oC)
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Other atomic absorption methods

• Methods having higher sensitivity than normal
  flame atomic absorption or electro-thermal atomic
  absorption
• Used for special elements including arsenic,
  selenium and mercury.
• Use chemical reactions in the process of
  atomization to vaporize in the form of an atom or
  simple molecule.

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Hydride Vapor Generation Technique

• As, Se, Sb, Sn, Te, Bi, Hg and other metals
  produce a metal hydride by this method

Elements Concentration (ppb)
As 520
Sb 520
Te 520
Bi 520
Se 1040
Hg 2080
Sn 3090
Absorption Cell
Burner Head of AAS
Peristaltic Pump
Manifold
Gas Liquid Separator
Reaction Coil
Drain
Sample
NaBH4
HCl
Carrier Gas Ar
Structural Diagram of Hydride
Vapor Generator
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Cold Vapor Technique
SnCl2
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Limit of Quantitative
Element Detection Limit Detection Limit
  Flame (ppm) Furnace (ppb)
Ag 0.04 0.01
Al 0.5 0.03
As 0.02 ppb (HVG) 0.2
As 0.4 -
Cd 0.012 0.003
Cr 0.08 0.015
Cu 0.04 0.008
Hg 0.01 ppb (cold vapor) -
Hg 0.2 ppb (HVG) -
Mg 0.0035 0.003
Mn 0.025 0.01
Ni 0.08 0.13
Pb 0.2 0.06
Se 0.3 ppb (HVG) 0.2
Sn 2 N2O-C2H2 2
Zn 0.01 0.01
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Interference effects

• Physical interference
• Spectral interference
• Chemical interference

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Physical interference

• Flame
• Spray efficiency fluctuations due to difference
  in viscosity and surface tension between the
  standard and sample.
• Furnace
• Sample dispersion
• Measurement value fluctuations due to tube
  temperature distribution
• Viscosity within the graphite furnace
• Adherence to sample tip causing errors in
  collection quantity.
• Example samples, such as blood or juice,
  containing numerous organic components.

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Spectral interference

• Spectral absorption line overlapping with the
  absorption line of the target element.
• Absorption and scattering by molecules

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Spectral interference
Spectral absorption line overlapping with the
absorption line of the target element.
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Spectral interference

• Absorption and scattering by molecules
• Molecules absorption
• Alkaline metals Halogens Alkali halides
• (Na, K)(F, Cl, Br, I) (Ex NaCl, KI)

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Chemical interference

• Generation of non-separable compounds by
  coexisting matrices
• Example influence of PO4-, SO4-, SiO2
  relative to Ca, Mg
• in flame analysis
• (generation of Ca2PO4)
• Generation of low boiling point compounds by
  coexisting matrices
• Example influence of chloride ions relative to
  Cd in
• furnace analyses
• (generation of CdCl2)

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Matrix modifier effect

• Masking of obstructing matrices
• Influence of phosphate on Ca is masked by La
• Conversion of obstructing matrices to compounds
  that easily undergo sublimation or evaporation
• Sublimation agent
• Example removal of chloride ion by ammonium salt
  of nitric acid or phosphoric acid
• Conversion of measured elements to stable oxides
  or metallic intermediary compounds
• Stabilizing agent
• Example creation of measured element alloy using
  white metals (Pd, Pt, Rh)

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Application examples of the matrix modifier
method
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Standard Addition Method
No.4
No.1
No.2
No.3
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Standard Addition Method
Calibration Curve of Standard Addition Method
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2-Way Background Correction is Standard
Background Correction

• D2 lamp method (? 190-430 nm) Molecular
  absorption

• Self-Reversal (SR) method Spectra interference

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Elements/ wavelengths where spectral interference
becomes problematic
Background Correction
Spectral interference
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Background Correction
Self-Reversal Method
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Background Correction
Self-Reversal Method
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Atomic Absorption Spectrophotometer
AA-6300
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High Performance Optical System

• Optical diagram of Double Beam System

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Easy Switching between Flame and Furnace
Flame -gt Furnace All that is involved is to
remove the burner head, place the furnace unit,
and fix it with the screw. No tools are required.
Remove the burner head.
Fit the furnace.
Fit the burner head.
Remove the furnace.
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New Flame Atomizer
For chemical resistance

• Neburizer w/ Ceramic made Impact Bead
• Polypropylene-made Chamber
• Solid Titanium-made Burner Head

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High Productivity

• Full Auto ASC- Auto measurement up to 60
  samples- Reagent addition 8 position
  - Automatic dilution
• Optimize Flame analysis- Automatic search the
  best fuel gas flow rate- Automatic search the
  Optimize Flame analysis best
  burner height

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Enhanced Safety

• Auto Gas Leak Check
• Gas pressure monitoring to prevent flashback
• Automatic flame monitoring
• Automatic flame extinguish when
• power failure
• Safety interlock for burner misuse
• Auto Air/N2O flame changeover
• Drain level sensor

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Wizard Software System
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Automated/ Optimized
Effectiveness of the automatic Line Search/Beam
Balance
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Effectiveness of the automatic burner height
Automated/ Optimized
(Cr 4ppm standard solution used)
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Search for the optimal fuel flow rate
Automated/ Optimized
(Cu 4ppm standard solution used)
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Screen during measurement
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User Management

• The Login ID and password need to be entered
  when the software is started up.
• Records of who logged in at what time are
  preserved in the Event Log.

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User ManagementAuthority can be set in detail
for each user
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Initial Validation Screen
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Summary Validation Report
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Applicationof Atomic Absorption
Spectrophotometry
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Application of AAS
AAS
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Pretreatment

• Precautions for pretreatment
• Dissolve all the elements into the same solution
  evenly.
• (Check with certified reference material.)
• Ensure that elements are not lost in the
  solution. i.e., due to vaporization or
  sedimentation (Check with recovery test.)
• Contamination Purified water, reagent (e.g.,
  acid), container, environment. (Check with blank
  operation.)
• Ensure that the solution to be analyzed is stable
  for a long time (i.e., no hydrolysis or
  sedimentation).
• Consider the interference effect of the reagent
  on the analysis values.

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Types of Pretreatment

• Dilution
• Dilute the sample with purified water, dilute
  acid, or organic solvents.
• Examples food products (e.g., dairy products),
  pharmaceuticals, and biological samples (e.g.,
  blood, urine).

• Dry Decomposition
• Heat the sample to a high temperature (400 to
  500?C), Decomposition is possible in a short time
  (a few hours) and operation is simple.
• Elements with low boiling points (e.g., Hg, As,
  Se, Te, and Sb) will vaporize

• Wet Decomposition
• Heat the sample together with acid to a low
  temperature (approx. 300?C). Suitable for
  volatile elements.
• A long time is required for the decomposition of
  organic substances.

• Microwave Decomposition
• Decompose the sample at high pressure by heating
  it together with acid to a temperature in the
  range 100 to 200?C in a sealed Teflon container.
• The decomposition process is sealed there is
  little vaporization of elements with low boiling
  points the decomposition time is short there is
  little contamination from the operating
  environment and the reagent and only a small
  amount of acid is required.
• Examples Sediment, soil, dust, ceramics, living
  organisms, food products, etc.

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Wet Decomposition Method
Kjeldahl flask wet decomposition method
Waste gas
Cooling tube
Nitric acid
Simple method (no cooling)
SampleSulfuric acid
Heating
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Pretreatment Microwave Decomposition

• Decompose the sample together with an acid in a
  sealed container.
• Decomposition possible in a short time with
  little vaporization or contamination.
• - Ideal for the pretreatment of trace elements
  and trace samples.
• - Food products, living organisms,
  pharmaceuticals, airborne dust, soil, etc.

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Sample Preparation using Pressure Digestion with
Microwave heating
Digestion Vessels 1 - 12
Microwavepower
Pressure measurement
Temperaturemeasurement
internal PC or Controller
Control by Tmax and Pmax
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Pretreatment Solubility of Elements in Samples

• Total Content

Inorganic compounds with low solubility Sulfides,
oxides, silicates, etc.
Simple soluble metals compounds Carbonates,
oxides, etc.
Organic compounds
Simple water-soluble ions
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Example
Application of AAS
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EU Regulation for Hazardous Substances
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EU Regulation for Hazardous Substances
IEC Recommendation for RoHS
RoHS Restriction of Hazardous Substance in
Electrical and Electronic equipment.
Substances Polymers Metals Electronics
PBB/PBDE 1000 ppm GC-MS NA GC-MS
Cr6 1000 ppm Colorimetric Method (Spectrophotometer) Spot-test procedure/boilingwater- Extraction procedure (Clause8) Colorimetric Method (Spectrophotometer)
Hg 1000 ppm Cold Vapor-AAS, ICP Cold Vapor-AAS, ICP Cold Vapor-AAS, ICP
Pb 1000 ppm Cd 100 ppm AAS, ICP AAS, ICP AAS, ICP
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Preparation of circuit boards
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Sample Preparation
Target Element Pretreatment Methods Pretreatment Methods Pretreatment Methods Pretreatment Methods Pretreatment Methods
Target Element Polymer Polymer Metals Metals Electronics
Hg   Microwave digestion (HNO3 HBF4 H2O2)     Microwave digestion (HNO3 HBF4 H2O2)     Microwave digestion (HNO3 HBF4 H2O2)     Microwave digestion (HNO3 HBF4 H2O2)     Microwave digestion (HNO3 HBF4 H2O2)  
Cd Pb Microwave digestion (HNO3H2O2) (If contain ing Si, Ti add HF) a) Common method (HCl HNO3 water 2 1 2) b) If containing Zr, Hf, Ti, Ta, Nb, W (HNO3 HF 1 3) c) If containing Sn (HCl HNO3 3 1) a) Common method (HCl HNO3 water 2 1 2) b) If containing Zr, Hf, Ti, Ta, Nb, W (HNO3 HF 1 3) c) If containing Sn (HCl HNO3 3 1) Microwave digestion Step A (HNO3HBF4H2O2) Microwave digestion Step B (add HCl) Microwave digestion Step A (HNO3HBF4H2O2) Microwave digestion Step B (add HCl)
Pretreatment method, which follow by IEC 62321
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Analyzing Cadmium (Cd) in RicePretreatment Using
Wet Decomposition
Level suggested by FAO/WHO Codex Committee 0.2
ppm max. in polished rice (proposed)
Put 5 g of the sample in a beaker. Add 30 mL of
nitric acid (11) and 0.5 mL of sulfuric
acid. Warm on a hot plate until the violent
reaction subsides. ? Perform thermal
decomposition until the contents approach a
hardened and dried state. When the contents turn
dark brown, add 1 mL of nitric acid. Repeat this
process. When the contents turn light yellow or
become transparent, expel the white smoke of the
sulfuric acid and leave to cool. Add nitric
acid. Heat on the hot plate to dissolve the salt
content. Leave to cool. Dilute for measurement.
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Results of Quantitative Analysis of Cd in Rice
The following 2 methods can be used to analyze
unpolished and polished rice decomposed using
acid
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Summary of Methods for Analyzing Cd in Rice

• Comparison of Pretreatment Methods
• Wet oxidation 3 to 5 hours Dry ashing 5
  to 10 hours
• Microwave 1 hour Acid extraction 2 hours

• Expected Lower Limits for Quantitative
  Measurement
• Flame method 0.100 ppm
• Furnace method 0.001 ppm

• Comparison of Measurement Times for Each
  Measurement
• Method (n3)
• Flame method 30 s
• Furnace method 360 s

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of Atomic Absorption Spectrophotometry
Preventive Maintenance / Calibration
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Preventive Maintenance/Calibration
Maintenance
Weekly check

1. Cleaning the Burner head

Clogged (by carbide or salt etc.)
Normal
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Preventive Maintenance/Calibration
Maintenance
Weekly check
2. Cleaning the Chamber with diluted water or
alcohol
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Preventive Maintenance/Calibration
Maintenance
Weekly check
3. Cleaning the Nebulizer
Nebulizer
Do not apply the ultrasonic cleaner to the
nebulizer
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Hardware Validation
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Preventive Maintenance/Calibration
Calibration
(12 Month)

• 1. Wavelength Accuracy
• - Using Hg hollow cathode lamp set at
  Emission mode
• - Measure peaks should be within 0.7 nm
• (253.6nm 365.0nm 435.8nm 546..1nm
  585.2 640.2nm)

2. Noise Level - Using Se hollow cathode
lamp (? 196 nm) - NON-BGC Noise level should
be lt 0.015 Abs. - BGC-D2 Noise level should
be lt 0.035 Abs.
3. Baseline Drift - Using Cu hollow cathode
lamp (? 324.8 nm) - Measuring time 1800 sec
- Measured value less than 0.006 Abs
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Preventive Maintenance/Calibration
Calibration
(12 Month)
4. Absorption - Using Cu hollow cathode
lamp - Standard Cu 2 ppm - Measured
value more than 0.23 Abs

• 5. Repeatability
• - Using Cu hollow cathode lamp
• - Standard Cu 2 ppm
• - Measure 5 time and CV value lt 2

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Preventive Maintenance/Calibration
Calibration
(12 Month)
6. Detection Limit - Using Cu hollow
cathode lamp - Standard Cu 2 ppm -
Measure Standard is 3-5 time and calculate the
mean value (A) - Measure Blank solution is
3-5 time and calculate the standard deviation
(S) - Take the obtained value as the
detection limit lt 0.004 Abs. Detection
limit (2.0 x 3 x S) / A
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Preventive Maintenance/Calibration
Calibration
(12 Month)
7. Stability - Using Se and Cu hollow
cathode lamp - Standard Cu 2 ppm -
Measure std. Cu around 5 sec (B) - Measure
std. Cu continuous around 30 sec and measure
amplitude of Abs. value (W) - Take the ratio
of W to B Stability W/B lt 6.0
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Preventive Maintenance/Calibration
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Thank You