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FUNDAMENTAL OF ATOMIC ABSORPTION SPECTROSCOPY Shimadzu (Asia Pacific) Pte Ltd Singapore Copyright © Shimadzu (Asia Pacific) Pte Ltd 2006. All rights reserved.

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CSC/CAM/AA/003/Jul2006

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Atomic Spectra Development Flame Emission Atomic Absorption Atomic Fluorescence ICP-MS

1950

1960

1970

1980 Year

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1990

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Concentration Coverage

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History Of Shimadzu AAS

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Year

Shimadzu AAS

1968 1970 1972 1975 1976 1978 1979 1983 1985 1985 1988 1988 1990 1991

MAF AA-600 AA-610 AA-620 AA-625/630 AA-640 AA-646 AA670/670G AA-660 SPCA-626D AA-680, AA-680G AA-660G SM-30 AA-6500 series

Remarks

SR background correction method Soil and plant clinical analyzer CRT user's interface GFA-4B Zeeman AAS (Direct solid sampling) Fully automated and tandem atomizer

1993 1994 1995 1996 1997 1998 1999 1999 2002

AA-6400 series AA-6600/6700 series SPCA-6610 AA-6200 ASC-6100 AA-6800 AA-6650 GFA-EX7 AA-6300

High performance middle-class AAS PC controlled AAS Soil and plant clinical analyzer Double-beam AAS with PC windows Autosampler for flame and GFA High-end and WizAArd software Middle-end and WizAArd software Graphite furnace for AA-6800/AA-6650 Double-beam flame and WizAArd software

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Atomic Absorption hν E2

hν

eNucleus

E1

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e-

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Atomic Absorption E = E2 - E1 = hν λ =c/ν λ = hc/ (E2 - E1 ) E2 = E1 = h = ν = C =

Excited state Ground state Planck’s constant Spectral frequency Speed of light

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E2

hν

E1

e-

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Sodium Lines eV 6 4

3.6 eV 2.2 eV

330.3 nm

2 589 nm

Ground state SHIMADZU

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Io

Atomic Vapor

I

l

Lambert-Beer’s Law

I = Io e-klc T = (I/Io) x 100% A = log (Io/I) = klc where T = transmittance, A = absorbance, k = molar absorptivity, c = concentration of atomic vapour

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AAS Instrumentation 1) Radiation source (hollow cathode lamp) 2) Sample conversion to free atoms (atomizer) 3) Optical system (single/double beam) 4) Monochromator 5) Detector (photomultiplier tube) 6) Signal processor and output display SHIMADZU

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AAS Instrumentation

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(1) Light Source

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Hollow Cathode Lamp (HCL)

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Hollow Cathode Lamp Ar + eAr+

Ar+ + 2e-

Ar + M(s)

M(g)

Ar

Cathode

M(g)

e-, Ar+

M*(g)

M*(g)

Anode

M M M M

M(s)

M Ar

Ar Light

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Ar

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Lamp Management ♦Eight-turret lamps placement ♦Records of lamp information ♦Records of lamp history

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Lamp Management

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Hollow Cathode Lamps ♦ Hamamatsu HCLs are recommended. However, HCLs from other suppliers can be used if: 9 the dimensions are same as in diagram below. 9 the maximum operating current is higher (or same) than operating current used in WizAArd software.

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Super Lamps ♦Produce radiation intensities (brightness) 10 times greater than HCLs. ♦High precision measurement as S/N is greatly improved. ♦Useful for As, Se, Te, Hg, Pb where the HCL intensities are low. SHIMADZU

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Super Lamps

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Super Lamps

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(2) Atomizer

Creation of Free Atomic Vapor! SHIMADZU

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Atomization The process of converting the analyte into free atoms to emit or absorb light energy. Nebulization Solution

Flame

Aerosol

Free Atomic Vapor

Furnace heating

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2 Types Of Atomizer 1) Flame 2) Flameless a) graphite furnace AAS (GFA) b) hydride vapor generator (HVG) c) mercury vapor unit (MVU)

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Atomizer I

Atomic Vapor

Io

l In flame, l = length of burner head In GFA, l = length of graphite tube

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Flame Atomization

Flames are formed by combustion of an oxidant and a fuel mixture, i.e. air, nitrous oxide, Ar, H2, acetylene.

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Flame Atomization Process

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Flame Atomization Steps ♦ Nebulization. ♦ Desolvation of droplets. ♦ Vaporization of solids. ♦ Dissociation of molecular species. ♦ Ionization of analyte atoms. SHIMADZU

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Nebulization ♦ The sample introduction system disperses the sample solution onto the impact bead ♦ This causes the sample solution to change into fine spray or mist which can be carried by gases upwards to the flame.

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Desolvation Of Droplets ♦ The desolvation leaves a dry aerosol of the molten or solid particles. ♦ This often begins in the nebulization step. ♦ Organic solvents evaporate more rapidly than water. SHIMADZU

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Vaporization Of Solids The solids or molten particles remaining after desolvation must be vaporized to obtain free atoms [MX(gas) M(gas) + X(gas)].

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Vaporization Efficiency ♦ Depends on bond dissociation energies of compounds. ♦ Flame conditions - high temperatures and a reducing environment tend to increase the volatilization efficiency and reduce the formation of refractory oxides. ♦ Aerosol size - the vaporization increases as the size of droplets introduced into the chamber decreases. ♦ Incomplete vaporization - results in non-linearity in calibration curve and continuous background emission by molecular species.

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Flame Structure The burning velocity is a fundamental parameter of the gas mixture and it is important in determining the flame shape and stability.

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Selection Of Flames ♦ Air-C2H2 Flame Temperature (oC) Ar - H 1577 Most elements. Air-H 2045 ♦ N2O- C2H2 Air-C H 2300 N 0-C H 2955 Refractory elements e.g. Al, V, Ti etc. ♦ Ar-H2 Absorption wavelength at UV range e.g. As, Se, Zn, Pb, Cd, Sn 2

2

2

2

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Light Absorption Of Flames N2O-C2H2 flame (N2O 7 l/min, C2H2 6 l/min) Ar-H2 flame (Ar 8.6 l/min, H2 10 l/min) Air-H2 flame (Air 10 l/min, H2 28 l/min) Air-C2H2 flame (Air 10 l/min, C2H2 6 l/min)

Burner height: 5 mm Flame length: 5 cm for only N2O-C2H2 flame; 10 cm for other flames

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Atomic Vapour Population

Burner height and fuel composition affect the atomic mist distribution.

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Burner height and fuel composition do not have much affect on atomic mist distribution.

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Atomic Vapour Population

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Air-propane/Air-LPG Flame ♦ LPG comprises of a mixture of propane and butane, e.g. 40% propane and 60% butane. ♦ LPG is generally cheaper than acetylene. ♦ Air-Propane and Air-LPG flame have lower temperature compared to Air-C2H2 flame, about 2200 K, so it is suitable for the analysis of alkaline earth metals. ♦ Air-Propane and air-LPG flame have better sensitivity than Air-C2H2 flame but noise is higher. SHIMADZU

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Air-Propane Burner Head

Front view Side view SHIMADZU

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Flame Atomizer ♦ In AA-6800/6650/6300. ♦ Integrated high performance nebulizer with highly chemical resistant ceramic impact bead - can withstand corrosive acids such as HF and organic solvents. ♦ Solid corrosive-proof titanium burner head. ♦ Burner head can be easily installed and removed for cleaning. ♦ Polypropylene chamber is set at 15o angle to horizontal to ensure proper drainage. ♦ Absorbance readings are more stable as big droplets are removed by mixer. ♦ Guaranteed sensitivity for 2 ppm Cu is 0.230 Abs, maximum RSD is 2%.

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AA-6800/6650/6300

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Graphite Furnace AAS (GFA)

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GFA ♦Also known as electrothermal. ♦The graphite furnace tube is continually bathed in an inert gas (i.e. Ar) to prevent the furnace from oxidation. ♦Inert gas reduces the oxide formation and increases the atomization efficiency. SHIMADZU

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GFA Atomization Process

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GFA Atomization Steps ♦Drying or desolvation step ♦Ashing step ♦Atomization step ♦Cleaning step (optional)

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(1) Drying Step ♦Like the desolvation step in flame AAS, the solvent is removed. ♦Generally the heating temperature is set at 60-150oC for water-based samples and 50-100oC for organic-based samples. ♦The chosen temperature should ideally evaporate the solvent as rapidly as possible without spattering.

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(2) Ashing Step ♦During this stage, organic matter in the sample is ashed or converted into water, CO2 and volatile inorganic compounds. ♦Ideally, the temperature should be high enough to remove all volatile components without loss of the analyte.

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(3) Atomization Step ♦The analyte is vaporized and atomized to produce atomic vapor at around 20003000oC. ♦At the end of the atomization stage, the atomic vapor is rapidly diffused out of the observation zone.

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(4) Cleaning Step ♦To evaporate remaining metal and salt which remains in the graphite tube. ♦Carried out at 3000oC but lower temperature desirable. ♦Cleaning temperature is normally atomization temperature plus 200oC.

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Temperature (oC)

GFA Heating Steps Atomization step

Cleaning step (option)

Ashing step Drying step Time (s)

0

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Outer gas (Ar) Inner gas (Ar) Inner gas (O2)

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Graphite Tubes 1) High density graphite tube 2) Pyrolytic graphite tube 3) Platform type graphite tube

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Graphite Tubes Sample Injection Port

High density graphite tube Sample Injection Port

Pyrolytic graphite tube SHIMADZU

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Platform Type Graphite Tube Sample Injection Port

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ENLARGED GRAPHITE TUBE ♦ In the new design, the middle part of the tube is enlarged, compared to the end. ♦ This is to ensure that the whole tube is heated up in a uniform manner. R R R R R

R

Small graphite tube T(°C)

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ENLARGED GRAPHITE TUBE ♦Reduces background noise and hence increases sensitivity. Slit width

Small graphite tube

Slit width

Enlarged graphite tube SHIMADZU

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ADDITIONAL SLIT WIDTH ♦In AA-6300. ♦0.2 and 0.7 nm can be used for flame analysis. ♦Additional 0.7 (low) and 2.0 (low) nm can be used for graphite furnace analysis to reduce radiation effect when the tube is heated to more than ~ 2000oC.

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2 Heating Methods (1) Current Control Method Temperature of graphite tube is correlated to current provided to the tube. (2) Temperature Control Method Temperature of graphite tube is correlated to infrared rays emitted by graphite tube which is measured by photosensor

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Temperature (oC)

Heating Methods Graphite tube deteriorates, R increases, temperature increases

Drying

Ashing

Current Control Method

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Temperature Control During Atomization

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Current Control Method Drawbacks ♦The sample droplet tends to boil off during drying step. ♦The target elements are scattered in the graphite tube during ashing step. SHIMADZU

Extended Temperature Control Temperature (oC)

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Temperature control has been extended to ashing step, accuracy increases.

Drying

Current Control Method

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Ashing

Temperature Control During Atomization

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Auto Current Correction Temperature of graphite tube (oC)

Heating current of 100oC (A)

100oC

100

200

300

400

500

600

No of graphite tube being heated

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High Sensitivity GFA

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Improved Structure ♦Extended volume with presence of window socket increases the retention time of the atomic vapor on the optical axis hence increasing the sensitivity. ♦The graphite tube is protected from outside air by a Teflon seal so that the tube can last longer.

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Improved Structure NEW

Pushing force due to heating.

OLD Spring

Pushing force due to heating.

This results in smoother, less restricted movement to obtain more reproducible results.

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Merits of GFA Design ♦High sensitivity. ♦Long lifetime of graphite tube. ♦Best suited for continuous multisample analysis. ♦Reduction of running cost.

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Good Reproducibility Measurement Of Cr Sample

(< 2% CV)

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Long Lifetime Of Graphite Tube Measurement Of Cr Sample

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Optional Furnace Program ♦ The original furnace heating program is suitable for aqueous-based sample.

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Optional Furnace Program ♦ The Hot Injection program is suitable for analysis of organic solvent, samples with high acid concentration and pure water samples. ♦ Here, the graphite furnace tube is heated first before sample is injected. This prevents sample from spreading and causing high background. ♦ The ASC-6100 arm is replaced with a polymerbased arm to prevent corrosion.

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Single-Body Dual Atomizer Flame/GFA AutoSwitching

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Dual Atomizer ♦ Easy switch over between GFA and flame atomizer. ♦ High Precision xand y-axis motorized movement. ♦ Available in model AA-6701 and AA-6800. SHIMADZU

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Manual Switching ♦ Available in AA-6300. ♦ To change from flame to furnace mode, just 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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ASC-6000/6100 Auto Sampler ♦Improves productivity for multiple samples. ♦Preparation of calibration standards. ♦Auto-dilution of samples. ♦Addition of matrix modifiers. ♦For flame microsampling and GFA.

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ASC-6000/ASC-6100 ASC-6000

ASC-6100 SHIMADZU

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Auto-Sampling Unit

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Mixing Mode

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Auto-Dilution - GFA

9 Cu Calibration Curve. 9 Preparation of 40, 80, 120, 160 ppb with automatic dilution of 200 ppb Cu.

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Flame Microsampling Available with AA-6601/6701 with ASC-6000 and AA-6300 with ASC-6100

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Flame Microsampling ♦ Unlike the usual continuous flame suction method, about 50 to 100µL of the sample is injected into the flame in one go. The sample is quantitated using the peak-shaped signal obtained. ♦ Only a small amount of sample is required. ♦ Blockages of the burner slot are less common, even with high salt content samples. ♦ Together with the auto sampler, automatic dilution measurements are possible.

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Flame Microsampling Sampling Port

Sampling Port

Solenoid valve closed

Solenoid valve open

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Flame Microsampling ASC-6000

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Flame Microsampling ASC-6100

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Auto-Dilution - Flame Microsampling

9 Flame Analysis (Calibration curve/Micro-sampling). 9 Calibration curve developed using auto-dilution of 2 ppm Cu standard solution. 9 Sample injection volume 100 µl.

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Flame Microsampling Parameter Element: Cd Wavelength: 283.3 nm Slit: 0.7nm Air-C2H2 flame C2H2：1.8L/min，Air：8L/min auto sampler Cd Conc. 1 ppm Cd H2O Total 0.0 ppm 0 uL 100 uL 100 uL 0.2 ppm 20 uL 80 uL 100 uL 0.4 ppm 40 uL 60 uL 100 uL 0.8 ppm 80 uL 20 uL 100 uL

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HVG ♦ Hydride Vapour Generator. ♦ For volatile elements such as arsenic (As), selenium (Se), antimony (Sb), tin (Sn), bismuth (Bi), tellurium (Te). ♦ Conversion of elements to metal hydrides by sodium borohydride under acidic condition. ♦ Detection limit improved to ppb level. As calibration ♦ Suitable for curve environmental analysis. SHIMADZU

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HVG - Reaction As, Bi, Sb, Se, Sn, Te

Gaseous Hydride

HVG-1

Atomization Flame

BH4- + 3H2O + H+ 3BH4- + 3H + + 4H3AsO3

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Electrical heating cell

H3BO3 + 4H2 nascent hydrogen 4AsH3 + 3H2O + 3H3BO3

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HVG-1 - Flow Line

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HVG – Electrical Heater

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MVU ♦ Mercury Vapour Unit. ♦ Mercury ion in solutions reduced by SnCl2 to elemental mercury which vaporizes at room temperature. MVU-1 ♦ Suitable for environmental analysis of mercury in water. ♦ Can detect 0.1 ppb mercury SHIMADZU

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MVU – Flow Line

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Typical Detection Limits (ppb) Element

Flame AAS

Aluminium (Al) Antimony (Sb) Arsenic (As) Bismuth (Bi) Cadmium (Cd) Calcium (Ca) Copper (Cu) Lead (Pb) Manganese (Mn) Mercury (Hg) Nickel (Ni) Selenium (Sn) Tellurium (Te) Vanadium (V) Zinc (Zn)

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30 30 100 20 0.5 1 1 10 1 200 4 70 20 40 0.8

Graphite Furnace AAS 0.01 0.2 0.2 0.1 0.003 0.05 0.02 0.05 0.01 20 0.1 0.5 0.1 0.2 0.001

Mercury/ Hydride 0.1 0.02 0.02

0.008 0.02 0.02

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Flame vs GFA Atomization principle

Atomized through the heat of the flame

Sample usage rate (atomization efficiency)

Approximately 10 %

Atomized by the heat generated when a current is passed through a resistance bulb Over 90 %

Amount of sample required Shape of absorption signal Sensitivity Reproducibility Influence of coexisiting substances Measurement time

Approximately 1 ml Stationary signal Low (ppm level) Below RSD 1.0% Small Short 10 to 30 s per sample

5 to 50 µL Peak-shaped signal High (ppb level) About RSD 2 to 5% Large Long 1 to 5 min per sample

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Selection Of Method ♦Flame AAS applicable at moderate levels in complex-matrix system. ♦Flame AAS, solvent extraction is used for lower levels. ♦GFA can increase sensitivity (use matrix modifiers). ♦HVG for As & Se; MVU for Hg.

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Atom Booster

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Flame AAS vs GFA ♦ Flame AAS 9 High stability 9 Quick analysis 9 Measurement at ppm level

♦ Graphite Furnace AAS 9 Measurement of sub-ppb level 9 Need specific timings - drying, ashing, atomization processes

♦ Generally, high sensitivity measurement for Flame AAS is preferred as it is fast and gives stable results. SHIMADZU

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Boosting Sensitivity In Flame AAS ♦By sample preparation 9Accumulation by sample preparation

♦Improving nebulization efficiency 9Development of the high sensitivity nebulizer

♦Improving atomization 9Improvement of atomization in the flame

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Boosting Sensitivity In Flame AAS ♦ Sample preparation methods 9 Accumulation with the volatilization of the solvent. 9 Accumulation with solvent extraction. 9 Accumulation by the ion exchange resin. 9 Accumulation with the co-precipitation method which uses the chelating agent.

♦ Disadvantages 9 Time and time is required for sample preparation. 9 Contamination is possible.

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Boosting Sensitivity In Flame AAS ♦Improving nebulization efficiency 9High sensitivity nebulizer has been mounted as a standard in Shimadzu AAS.

♦Improving atomization 9Residence time of the atomized vapour is made longer. 9High sensitivity is achieved by Atom Booster ÄSensitivity improvement of 2 or 4 times.

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Atom Booster

Atom Booster

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Mounting on burner head

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Atom Booster Flame direction

Cross section of cell

Top view of cell 150 mm

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Principle Of Atom Booster Volatilization of atom Atom Booster

Creation of atom

Normal flame atomization SHIMADZU

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When Atom Booster is used

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Principle Of Atom Booster ♦As atomic vapor builds up in the quartz cell, the atomic density and sensitivity rises. ♦With Cd, Pb, Cu, Mn, Ni, Zn, and Sb, there is a sensitizing effect of 2 to 3.5 times.

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Sensitivity Comparison Element

1% Absorption (ppm) Sensitized Without With Ratio Booster Booster

As Cd Cu Fe Mn Ni Pb (217.0 nm) Pb (283.3 nm) Sb Se Zn

－ 0.0072 0.0230 0.0400 0.0250 0.0410 0.0800 0.1900 0.3300 － 0.0070

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0.0800 0.0030 0.0100 0.0300 0.0200 0.0200 0.0200 0.0500 0.0800 0.0500 0.0020

－ 2.4 2.3 1.3 1.3 2.1 4.0 3.8 4.1 － 3.5

Notes: ♦ Aqueous solution. ♦ 1% absorption value without atom booster was quoted from “Cookbook Section 3 Measurement condition by element by Flame AAS”. ♦ As for arsenic and selenium, the results were measured with air-acetylene flame.

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Sensitivity Comparison Element

1% Absorption (ppm) Without Booster With Booster

Cd Pb (217.0 nm) Pb (283.3 nm) Zn

0.0046 0.0500 0.1100 0.0061

0.0018 0.0200 0.0500 0.0025

Sensitized Ratio 2.6 2.5 2.2 2.4

Notes: ♦ Organic solution. ♦ MIBK used as the solvent.

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Pb Analysis Of Oil Standard Sample Absorbance

0.10

1.0 ppm 0.08 0.06

1.0 ppm 0.04

0.2 ppm

0.2 ppm

With Atom Booster

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1.0_5

1.0_4

1.0_3

1.0_2

1.0_1

0.2_5

0.2_4

0.2_3

0.2_2

0.2_1

1.0_5

1.0_4

1.0_3

1.0_2

1.0_1

0.2_5

0.2_4

0.2_3

0.2_2

0.00

0.2_1

0.02

Without Atom Booster

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Atom Booster - Limitations ♦The sensitivity of the following elements cannot be increased using atom booster: 9Alkaline (Na, K) and alkaline earths (Mg, Ca). 9The quartz cell reacts with silicon. 9Elements that require fuel-rich flame e.g. Cr, Sn, Os.

♦Atom Booster cannot be used for fireproof elements which use N2O–C2H2 flame (Ti, V, Mo, Al, Si). SHIMADZU

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Sensitivity Comparison Element Cd Cu Fe Pb Zn

1% Absorption (ppm) Shimadzu Varian Thermo 0.0030 0.0100 0.0300 0.0200 0.0020

0.0054 0.0214 0.0360 0.0400 －

0.0040 0.0100 － 0.0300 0.0030

♦ Product name differs in every supplier 9 Varian: Atom Concentrator 9 Thermo : Atom Trapper

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High Sensitivity Flame AAS ♦ High sensitivity nebulizer. ♦ Atom Booster. ♦ Depending upon these two combinations, it is possible to boost and achieve high sensitivity in flame AAS. ♦ Hitachi and Perkin-Elmer DO NOT have Atom Booster.

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Atom Booster is useful … ♦When higher sensitivity is required for flame AAS. 9Reduces accumulation time and cost, easy and sensitive measurement is possible.

♦Pb, Cd analysis 9Carbonated drink, Pb < 0.4 ppm. 9Medical supply container that is made from plastic.

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Atom Booster ♦P/N 206-50957-91. Consists of: 9206-50937-01 Quartz tube 9206-51099-91 Cell holder

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(3) Optical System ATOMIZER OPTICS

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AAS Optical System

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Single-Beam AAS

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Single-Beam Optical Systems

AA-6701 AA-6300 GFA AA-6800/6650

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Single-Beam (AA-6800/6650)

♦ BS: beam splitter ♦ G : grating ♦ M : mirror

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♦ S : slit ♦ W : window

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Electrical Double Beam Correction of Baseline Drift Raw Data Baseline Drift

Corrected Data

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Reslope Function ♦ Sensitivity correction function to minimise drift so that sensitivity of analysis is the same. ♦ This is done by checking sensitivity of analysis periodically using a standard solution. ♦ The software then calculates the drift and carry out correction on the following data.

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Double-Beam Optical Systems AA-6200

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Double-Beam Optical System

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AA-6300 – Optical System ♦ Flame : double-beam ♦ GFA : single-beam

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(4) Monochromator

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Monochromator Consists of: 1) Dispersive element (diffraction grating) 2) Image transfer system (entrance slit, mirror or lenses, and exit slit)

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Dispersive Grating ♦Consists of a plane or concave plate that is ruled with closely spaced grooves. ♦Different wavelengths are obtained when the plate is rotated at different angles.

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Monochromator

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123

3 Monochromator Designs 1) Czerny-Turner 2) Littrow 3) Fastie-Ebert

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Czerny-Turner Monochromator ♦ Rectifies aberration of astigmatism and reduces stray light.

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125

AA-6800/6650 ♦Blazed holographic grating (1600 lines/mm, with 33 x 30 mm area). ♦Focal length = 200 mm. ♦Automatic changeover of slit width (0.1, 0.2, 0.5, 1.0, 2.0, 5.0 nm).

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AA-6300 ♦Blazed holographic grating (1800 lines/mm, with 40 x 40 mm area). ♦Focal length = 300 mm. ♦Automatic changeover of slit width [0.2, 0.7, 0.7(L), 2.0 (L) nm].

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127

Littrow Monochromator

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Fastie-Ebert Monochromator

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129

(5) Detector

Photomultiplier Tube SHIMADZU

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Photomultiplier Tube ♦Consists of a photosensitive cathode and a collection anode. ♦Cathode and anode are separated by several electrodes called dynodes. ♦Dynodes emit 2 to 5 electrons when struck by an electron with sufficient energy. ♦Results in multiplication of electrons.

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131

Photomultiplier Tube

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(6) Signal Processing Unit

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133

Validation ♦Desire for self-inspection of equipment. ♦Desire to better understand the conditions of the equipment. ♦Desire to maintain the reliability of the data. ♦The AA-6800/6650/6701/6601/6300 validation system satisfies these desires.

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Validation The following items are important in maintaining the reliability of data: ♦Daily capability confirmation ♦Record of inspection results ♦Maintenance based on the above record

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135

Features Of Validation Program ♦ A total of 7 inspections are automatically executed based on standard operating procedures (SOP). ♦ Judgment, recording and output of inspection results. ♦ Change of inspection item parameters. ♦ Change of element measured, measurement wavelength, gas flow rate, and other parameters. ♦ Change of standard criteria. SHIMADZU

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Inspection Items ♦Wavelength Precision ♦Baseline Drift ♦Noise Level ♦Absorption Sensitivity (Flame and Furnace) ♦Repeatability (Flame and Furnace) ♦Stability (Flame) ♦Minimum Detectable Quantity (Flame)

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137

Operation Screen

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Can Make Changes

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69

139

Inspection Results

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Validation Program ♦ Control software, operating under MSWindows, improves ease of operation... ♦ Hardware with automation functions realizes greater efficiency... ♦ The atomizer section, already having the world top-level sensitivity, can execute analysis of even smaller quantities... Finally, the validation program is the doctor of the equipment! SHIMADZU

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Validation Program ♦ Leave it to us! ♦ From automatic analysis to machine management... ♦ Total planner, considering everything from to machine management, analysis the AA-6800/6650/6701/6601/6300 series validation system. ♦ Opens the Door to a New Age in AA Analysis.

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AAS Instrumentation

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143

INTERFERENCE IN AAS ANALYSIS & SOLUTIONS SHIMADZU

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Interference In AAS Analysis (1) Physical Interference

(2) Chemical Interference (3) Spectrophotometer Interference a) molecular absorption b) light scattering c) spectral interference

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145

(1) Physical Interference ♦In flame AAS, spray efficiency fluctuates due to differences in viscosity and surface tension between the standard and sample. Flame

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(1) Physical Interference ♦ Causes in GFA AAS 9 Sample dispersion - measurement value fluctuates due to graphite tube temperature distribution e.g. samples in organic solvents. 9 Sample viscosity - adherence to sampler tip causing errors in collection quantity e.g. samples such as blood or juice containing numerous organic components. Dispensing tube

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147

Physical Interference ♦Solutions 9Measurement by standard addition method. 9Flame AAS - carry out large dilution (10 to 50 times) or small dilution with acetone or butanol. 9GFA AAS - use pyrolytic/platform graphite tube. SHIMADZU

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(2) Chemical Interference ♦ Causes in flame AAS 9 Generation of various compounds from chemical reactions between components in the sample, e.g. in flame AAS, phosphate interference with regards to Ca, Mg, etc. (alkaline earth metals). 9 Ionic interference - shift of atom/ion equilibrium within the flame due to coexistence of metals with low ionic potentials e.g. influence of K during Na measurement or Na during K measurement.

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149

(2) Chemical Interference ♦Causes in GFA AAS 9 Generation of low boiling point compounds by coexisting matrices e.g. influence of chloride ions relative to Cd in furnace analyses (generation of cadmium chloride). This causes target elements to scatter at ashing step. 9 Influence of coexisting matrices e.g. samples with high O2 content such as biological samples. 9 Metals reacting with graphite tube to form carbides: ÒMetallic carbide - Ti, V, Mo, Cr ÒIntermetallic carbide - Mn, Co, Ni ÒHeteropolar carbide - Ca, Ba ÒDiamond type carbide - Si

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Chemical Interference ♦Solutions 9Removal of obstructing materials by ion exchange and solvent extraction. 9Target element extraction. 9Use the hotter N2O/C2H2 flame. 9Measurement by standard addition method.

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Chemical Interference ♦Solutions (cont) 9Ionization Buffers in flame ÒProvide an excess of electrons, to increase the free atom population of elements with low ionization potential ÒE.g. Cesium chloride, Cesium nitrate, Lithium chloride, Lithium nitrate, Potassium chloride, Potassium nitrate

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Chemical Interference Use interference suppressant to prevent ionization in N2O/C2H2 flame. Element

Ionization

Ionization Rate (%)

Energy (eV)

2000 K

Li

5.39

2.4

3000 K 97

Na

5.14

4.8

99

K

4.34

39.0

99.95

Mg

7.64

0.007

14

Cs

6.11

0.59

91

Sr

5.59

2.0

98

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153

Chemical Interference

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Chemical Interference ♦Solutions (cont) 9Use Releasing Agents in flame AAS ÒMinimize chemical interferences by combining with the interfering anions, liberating the element to be analyzed ÒE.g. Lanthanum chloride, Lanthanum nitrate

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Chemical Interference ♦Solutions (cont) 9Use Matrix Modifier in GFA ÒReduce the volatility of the analyte. ÒIncrease the atomization efficiency of the analyte by changing its chemical composition. ÒPermits the use of higher charring temperatures to volatile interfering substances and improve sensitivity. ÒIncrease the volatility of the matrix. ÒMagnesium nitrate, Palladium nitrate, Calcium nitrate, Ammonium phosphate, Ammonium nitrate, Nickel nitrate

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Chemical Interference ♦Matrix Modifier effect in GFA. NaCl + NH4NO3

NH4Cl + NaNO3 Decomposed at 400oC

Volatile Elements, e.g. + H3PO4 Cd, Pb

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Cd (PO4) Less volatile

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157

Chemical Interference Element Al Sb

Matrix Modifiers Mg nitrate Ni nitrate or Pd nitrate + Mg nitrate

Element Fe Pb

As Be Bi B Cd

Ni nitrate or Pd nitrate + Mg nitrate Mg nitrate Pd nitrate + Mg nitrate Ca nitrate Ammonium phosphate + Mg nitrate

Mn Ni Hg Se Ag

Cr Co Cu

Mg nitrate Mg nitrate Pd nitrate + Mg nitrate or Ammonium nitrate Pd nitrate + Mg nitrate Pd nitrate + Mg nitrate Pd nitrate + Mg nitrate

Te Tl Sn

Matrix Modifiers Mg nitrate or Ammonium nitare Ammonium phosphate + Mg nitrate or Ammonium nitrate Mg nitrate or Ammonium nitrate Mg nitrate or Ammonium phosphate Pd nitrate + Mg nitrate Ni nitrate or Pd nitrate + Mg nitrate Pd nitrate + Mg nitrate or Ammonium phosphate Pd nitrate + Mg nitrate Pd nitrate + Mg nitrate Pd nitrate + Mg nitrate or Ni nitrate

V Zn

Mg nitrate Mg nitrate

Ge Au In

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(3) Spectrophotometric Interference ♦ Causes a) molecular absorption b) light scattering c) spectral interference

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159

(a) Molecular Absorption ♦ Caused by undissociated molecules in the sample path, the absorption bands from molecules are usually broad in UV region.

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(b) Light Scattering ♦Caused by particles in the sample path, and also produces a broad-band effect.

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(c) Spectral Interference ♦ Caused by overlapping of the atomic absorption of an analyte and other free atoms in sample (two spectrals with close absorption wavelengths). ♦ Self absorbance if lamp current is too high. ♦ Absorption and scattering by molecules e.g. 9 Alkaline metals (Li, Na, K, Rb, Cs) + Halogens (F, Cl, Br, I) = Alkali halides e.g. NaCl, KI 9 Alkaline earth metals (Mg, Ca, Sr, Ba) + Halogens, -O, or -OH.

♦ Absorption by wings of resonance absorption lines.

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Spectral Interference Target Element

Spectral Line

Interfering

(nm)

Element

Spectral Line (nm)

Al

308.215

V

308.211

Ca

422.673

Ge

422.657

Cd

228.802

As

228.812

Co

252.136

In

252.137

Cu

324.754

Eu

324.753

Fe

271.903

Pt

271.904

Ga

403.298

Mn

403.307

Hg

253.652

Co

253.649

Mn

403.307

Ga

403.298

Sb

217.023

Pb

216.999

Si

250.690.

V

250.690

Zn

213.856

Fe

213.859

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Spectrophotometric Interference ♦Solution 9Removal of obstructing materials by solvent extraction. 9Background correction by instrument.

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BACKGROUND CORRECTION SHIMADZU

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165

Background Correction ♦ It is required when the sample contains other materials that can absorb light at the element wavelength. ♦ If no correction take places, the absorbance will be excessively high and the concentration of the element will be overestimated. ♦ Determination of analyte at UV region.

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Various Background Correction ♦Deuterium lamp correction for molecular absorption interference. ♦Deuterium lamp correction for light scattering by particles. ♦Spectral correction for spectral interference.

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167

(1) Deuterium Correction ♦The most common type of background correction where the effective range is up to 430 nm. ♦Corrects the molecular absorption and light scattering.

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Deuterium Correction

Mainly the background signal is determined. SHIMADZU

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84

169

High Modulation Frequency Deuterium Lamp (1000Hz)

Hollow Cathode Lamp (500 Hz) ♦ Increase signal sampling frequency (flameless AA) e.g. Pd or Cd where the transient absorption peak is about 1 sec.

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Limitations Of D2 Correction ♦No correction for spectral interference. ♦Different geometry and optical paths. ♦Loss of light due to the beam splitter. ♦Incorrect results in the presence of “structured” background. SHIMADZU

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171

Structured Background ♦ Structured background - backgrounds vary with wavelength, across the bandpass of monochromator. ♦ Results in over- or under-background correction.

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Spectral Correction ♦Self-reversal background correction. ♦Zeeman background correction. ♦Both are approved by EPA.

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86

173

SELF-REVERSAL CORRECTION

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Hollow Cathode Lamp

Ar + e-

Ar+ + 2e-

Ar

Ar+ + M(s) M(g)

e-, Ar+

Ar

Cathode

M(g) M*(g)

M(g)*

Anode

M M M M

M(s)

M Ar

Ar Light

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Ar

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175

Hollow Cathode Lamp High Current

Ar +

e-

Ar+

Ar+ + M(s) e-, Ar+

M(g)

+

2e-

M(g)

Ar

M M MM M M M MM M M

M*(g)

M*(g)

M(s)

Light

Cathode

Ar Anode

Ar

Ar

Absorbed

Ar M(s)

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Self-Reversal Correction ♦Step I 9The lamp is first run at a low current (i.e. 10mA) and its light is absorbed by the sample elements and background.

♦Step II 9Then a very brief pulse of high current (200mA) is passed through the lamp causing self-reversal and background is measured. 9Emission line becomes broader and the atomic absorbance from the analyte is greatly reduced hence it is called self-reversal.

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177

Self-Reversal Correction

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Self-Reversal Correction

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179

Self-Reversal Correction Zn measurements in metallurgical waste water samples BCG

Fe

Zn (0.05 standard)

Zn (0.10 standard)

Zn (0.2 stnadard)

Found

Deviation (%)

Found

Deviation (%)

Found

Deviation (%)

-

-

0.049

-2

0.099

-1

0.198

-1

-

100

0.059

+18

0.105

+5

0.211

+6

-

1000

0.101

+102

0.149

+49

0.247

+24

D2

1000

0.096

+2

0.143

+43

0.238

+19

SR

1000

0.049

-2

0.096

-4

0.193

-2

All amount in mg/l

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Measurement Of Zn In Fe When disparity arises between D2 and SR method. Atomic absorption Background absorption

②

⑤

①

⑥

Atomic absorption Background absorption ①

④

⑤ ③

③

Interval Width

④

Interval Width

Measurement of Zn in Fe solution by the BGC-D2 method

The absorbance of (6) is greater than (2) for the same 0.5 ppm Zn solution because of insufficient correction.

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⑥ ⑦

②

⑦

Measurement of Zn in Fe solution by the BGC-SR method

(2) and (6) of the same 0.5 ppm Zn solution has been corrected accurately and exhibit the same absorbance.

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90

181

Self-Reversal Correction Zn Standard Solution Absorbance (Abs)

BGC-D2

0.10

BGC-SR

0.05

0.1

0.2

Concentration (ppm)

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Self-Reversal Correction Zn in Fe, 1000 ppm Standard Solution Absorbance (Abs)

BGC-D2

0.10

BGC-SR

0.05

0.1

0.2

Concentration (ppm)

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91

183

ZEEMAN CORRECTION

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Zeeman Correction ♦Intense magnetic field cause atomic spectra lines to split into 2 or more components which can only absorb polarised light. ♦A polarizer can be used to separate these components so that (target element + background) and (background) can be measured. SHIMADZU

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92

185

Zeeman Correction ♦ There are different types of Zeeman correction depending on type of instrument configurations: 9 direct (magnet is directed at light source) vs inverse (magnetic field is located around the atomizer) 9 longitude (magnetic field orientated parallel to light beam) vs transverse (magnetic field orientated perpendicular to light beam) 9 ac (electromagnet) vs dc (permanent magnet)

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Zeeman Configurations ♦The 3 most popular configurations are: 9Inverse longitude ac Zeeman 9Inverse transverse ac Zeeman 9Inverse transverse dc Zeeman

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188

Inverse Longitude Ac Zeeman

♦ When magnetic field is off, light from HCL is absorbed by both analyte and background. ♦ In magnetic field, atomic lines in atomizer are split into two σ components which (ideally) cannot absorbed light from HCL. So, only background is measured. ♦ Not suitable for flame analysis.

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Inverse Transverse Ac Zeeman

♦ When magnetic field is off, analyte and background are measured. ♦ When magnetic field is on, atomic lines in atomizer are split into one π and two σ components. π and σ component absorbed light polarized in the plane parallel and perpendicular to magnetic field respectively. ♦ Polarizer is used to remove parallel radiation from the HCL. This allows only the perpendicular light from HCL to pass which is absorbed by σ component. So, only background is measured. ♦ Not suitable for systems with interchangeable flame/furnace analysis as there is a large magnet. Suitable for dedicated graphite furnace systems.

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190

Inverse Transverse Dc Zeeman

♦ When magnetic field is off, analyte and background are measured. ♦ When magnetic field is on, atomic lines in atomizer are split into one π and two σ components in magnetic field. π and σ component absorbed light polarized in the plane parallel and perpendicular to magnetic field respectively. ♦ A rotating polarizer alternately passes parallel (can be absorbed by π and background) and perpendicular radiation (can be absorbed by σ) from light source.

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Inverse Transverse Dc Zeeman Instrumentation

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95

192

Comparison D2 Lamp Correction

Self-Reversal Method

Wavelength Range

190-430 nm

190-900 nm

Zeeman Method 190-900 nm

Molecular Absorption

Yes

Yes

Yes

No

Yes

Yes

No

Yes

Yes

No

No

Yes

D2 Lamp

No Particular Parts

Polarizer and Magnet

Correction Spectral Interference Correction Deterioration of Sensitivity Loss of Light Intensity Instrumental Requirement Optical Adjustment

Necessary

Not Necessary

Not Necessary

Atomizing Unit

None

None

Specific

Specificity

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SAMPLE PREPARATION

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194

Sample Preparation

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Sample Pretreatment ♦To clean up samples. ♦Removal of interfering materials. ♦Separation of the element. ♦To decompose the organic substances by dry ashing, wet ashing methods, etc. ♦Method depends on nature of element, sample, potential interference, and analysis method. SHIMADZU

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196

Sample Pretreatment ♦ Precautions for pretreatment: 9 Dissolve all the elements into the same solution evenly check with certified reference material. 9 Ensure that elements are not lost (i.e. due to vaporization or sedimentation) in the solution - check with recovery test. 9 Contamination from purified water, reagent (e.g. acid), container, environment - check with blank operation. 9 Ensure that the solution to be analyzed is stable for a long time (i.e., no hydrolysis, sedimentation, or adsorption). 9 Consider the effect (interference) of the reagent (e.g. acid, salt concentration) on the analysis values.

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Sample Pretreatment ♦Dilution method: 9The sample is diluted using purified water, dilute acids, and organic solvents. 9Effective only for homogenous/uniform samples. 9E.g. food products (e.g. dairy products), pharmaceutical, wastewater, plating solution, lubricants, biological samples (e.g. blood, urine, etc).

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198

Sample Pretreatment ♦Treat inorganic samples in mineral acids (HNO3, HCl, H3PO4, H2SO4, HF, HClO4) normally with heating. ♦Convert organic samples by oxidative treatment to CO2 and H2O with: 9Dry ashing 9Wet ashing (digestion) 9High pressure decomposition e.g. microwave digestion. SHIMADZU

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Dry Ashing ♦ The sample is heated (400 to 550ºC) and combusted in an electrical furnace. ♦ Decomposes in a short time (a few hours). ♦ E.g. food products, plastics, organic powders, etc. SHIMADZU

CO2

Sample

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99

200

Dry Ashing Drying

Oxidation, Ashing

Acid dissolution

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Dry Ashing - Advantages ♦Large sample volume - multiple samples can be decomposed simultaneously. ♦Less contamination (minimum reagent required). ♦Simple operation.

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202

Dry Ashing - Disadvantages ♦Retention of elements on flask wall e.g. Co, Cu, Ag, Al, Mn and Fe on silica plate. ♦Formation of acid-insoluble compounds > 500oC e.g. Si, Al, Co, Be, Fe, Nb, Ta and Sn. ♦Loss of volatile (low boiling point) elements e.g. Pb, Hg, Cd, As, Se; Bi, Cu, Cr, Fe, Ni, Zn, V.

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Wet Ashing ♦ The sample & acid are heated at low temperatures (up to 300ºC) - suitable for volatile elements. ♦ E.g. iron & steel, non-ferrous metals, living organisms, food products, plastics etc. ♦ Boiling by using HCl or HNO3 - for extremely small amount of organic substances and suspensions. ♦ Decomposing by using HCl or HNO3 for samples contain -OH, oxide, sulfide phosphate. ♦ Decomposing by HNO3 and HClO4 organic substances hard to be oxidized.

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204

Wet Ashing Clean, readily oxidized sample

HNO3

Samples containing -OH, oxide, sulfide, phosphate

HNO3- H2SO4 HNO3-HCl

Difficult-to-oxidized organic samples

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HNO3- HClO4 or HNO3- HClO4 -HF

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Wet Ashing – H2SO4 & H2O2 Sample H2SO4 Digestion & Oxidation H2O2 Oxidation Boiling Remove H2O2

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Wet Ashing ♦ Kjeldahl flask. ♦ Compared to normal wet decomposition, there is little volatilization or external contamination. ♦ But not suitable to process multiple samples. ♦ For organic samples such as plastics e.g. based on EN1122. ♦ When analyzing As, Se, Hg, etc.

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Cooling tube

Nitric acid

Sample + sulfuric acid

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Wet Ashing - Advantages ♦Minimize the loss of volatile elements. ♦Oxidation at less drastic temperature.

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209

Wet Ashing - Disadvantages ♦ Organic matter takes a long time to decompose (from a few hours to several days). ♦ High possibility of contamination by oxidizing reagents - must watch out for contamination from the acid or the operating environment, such as the container and atmosphere.. ♦ Unavoidable loss of elements like As, Hg and Se. Use catalyst such as Mo(VI) or (V). SHIMADZU

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High Pressure Decomposition ♦ The sample and acid are placed in an airtight Teflon container and decomposed under high pressure (> 100 psi) while being heated to > than 100ºC. ♦ E.g. sediment, soil, dust, ceramics, living organisms, food products, etc. ♦ Microwave and pressure container decomposition 9 Sealed system decomposition, little volatilization of low boiling point elements, quick decomposition times. 9 Little contamination from the operating environment & reagent; little acid is used. 9 E.g. sediment, soil, dust, ceramics, living organisms, food products, etc.

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High Pressure Decomposition ♦ The sample and acid are decomposed in a closed vessel at high temperature (up to 200ºC), and high pressure (> 100 psi). Features: 9 Decomposition takes short time. 9 No volatilization during decomposition thanks to sealed system. 9 Little contamination from the processing compartment or acid.

Super pressure resistant container

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Microwave Decomposition ♦ Decomposition takes short time. ♦ No volatilization due to sealed system. ♦ Little contamination from processing compartment or acid. ♦ Through PC control, decompositions can be conducted under the same conditions, making routine work possible. ♦ Safety function (temperature/ pressure). ♦ Optimal for trace elements, and samples where only small amounts have been collected.

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Alkaline Fusion ♦ The sample is fused with alkaline flux by heating to a high temperature Na2CO3 e.g. 1000oC) ♦ For metallic compounds and ceramics, high Fusion molecular weight and complex samples e.g polymers, sand, etc. ♦ The sample will have a high salt concentration – Acid dissolution interference and contamination have to be taken into account. SHIMADZU Access To Your Success Sample

214

Sample Pretreatment Total Content Simple water-soluble ions

Simple soluble metals & compounds

Organic compounds

Carbonates, oxides, etc. Dilution, Elution Purified water, solvents, etc.

SHIMADZU

Inorganic compounds with low solubility Sulfides, oxides, silicates, etc

Wet Decomposition

Dry/Wet Decomposition

Hydrochloric acid, nitric acid, etc.

High-pressure Decomposition Nitric acid, sulfuric acid, etc.

Alkali Fusion Wet/High-pressure Decomposition Hydrofluoric acid, nitric acid, etc.

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106

215

Solvent Extraction Method ♦Extracting element in solvent which does not mix with water. ♦Chelate extraction system at optimum pH value.

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Solvent Extraction Method ♦Solvents MIBK, ethyl acetate, isobutyl acetate, amyl acetate, MEK.

♦Chelating Reagents Sodium diethyl dithiocarbamic acid (NaDDC) Ammonium pyrrolidine dithiocarbamic acid (APDC) SHIMADZU

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217

Solvent Extraction Method Chelating agents

Elements

Metal-chelates

Solvent Extraction

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218

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Solvent Extraction Method ♦ Can increase concentration of target element e.g. 100 ml sample is reduced to 10 ml MIBK. In this case, the concentration is increased 10 times. ♦ With higher concentration, it might be possible to analyse the sample using flame AAS instead of using another more sensitive method e.g. graphite furnace method. ♦ Suitable for samples with complex matrix e.g. seawater, biological samples (blood, serum, etc). SHIMADZU

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Workflow - Example 1 Sample Acquistion Filtering (Protect Nebulizer)

Filtered solution

Measurement

Residuals

Concentration

Solvent extraction

Decomposition Filtration

Measurement

Measurement

Concentration

Measurements

Measurement

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220

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Workflow - Example 2 Sample Hydrolysis Filtration

Filter solution

Residual Melting agent Fusion Acid Dissolution

Measurement

SHIMADZU

Measurement

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109

221

Thank you!

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