Lò Graphite -Quang phổ hấp thu nguyên tử

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Access To Your Success

FUNDAMENTALOF ATOMIC

ABSORPTION SPECTROSCOPY

Shimadzu (Asia Pacific) Pte Ltd SingaporeCopyright © Shimadzu (Asia Pacific) Pte Ltd 2006. All rights reserved. CSC/CAM/AA/003/Jul2006

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Flame Emission

Atomic Absorption

Atomic Fluorescence

ICP-MS

Year1950 1960 1970 1980 1990

Atomic Spectra Development

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Concentration Coverage

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History Of

Shimadzu AAS

Year Shimadzu AAS Remarks1968 MAF1970 AA-6001972 AA-6101975 AA-6201976 AA-625/6301978 AA-6401979 AA-6461983 AA670/670G1985 AA-660 SR background correction method1985 SPCA-626D Soil and plant clinical analyzer1988 AA-680, AA-680G CRT user's interface1988 AA-660G GFA-4B1990 SM-30 Zeeman AAS (Direct solid sampling)1991 AA-6500 series Fully automated and tandem atomizer1993 AA-6400 series High performance middle-class AAS1994 AA-6600/6700 series PC controlled AAS1995 SPCA-6610 Soil and plant clinical analyzer1996 AA-6200 Double-beam AAS with PC windows1997 ASC-6100 Autosampler for flame and GFA1998 AA-6800 High-end and WizAArd software1999 AA-6650 Middle-end and WizAArd software1999 GFA-EX7 Graphite furnace for AA-6800/AA-66502002 AA-6300 Double-beam flame and WizAArd software

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Atomic Absorption

E2

E1e-

hνe-

hν

Nucleus

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E2

E1e-

hν

E2 = Excited stateE1 = Ground stateh = Planck’s constantν = Spectral frequencyC = Speed of light

Atomic AbsorptionE = E2 - E1

= hνλ = c / νλ = hc/ (E2 - E1 )

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Sodium Lines

2.2 eV

589 nm

Ground state

eV

2

4

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3.6 eV

330.3 nm

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Io IAtomic Vapor

l

Lambert-Beer’s LawI = Io e-klc

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

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1) Radiation source (hollow cathode lamp)2) Sample conversion to free atoms

(atomizer)3) Optical system (single/double beam)4) Monochromator5) Detector (photomultiplier tube)6) Signal processor and output display

AAS Instrumentation

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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

M

MM

M

M

ArAr

Ar

Cathode

Ar

Ar

Anode

Ar + e- Ar+ + 2e-

Ar+ + M(s) M(g)

M(g) M*(g)

M*(g) M(s)

Light

e-, 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:

the dimensions are same as in diagram below. 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, Pbwhere the HCL intensities are low.

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Super Lamps

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Super Lamps

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(2) Atomizer

Creation of Free Atomic Vapor!

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

Nebulization

AerosolFreeAtomicVapor

Furnace heating

Flame

Atomization

Solution

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2 Types Of Atomizer1) Flame2) Flameless

a) graphite furnace AAS (GFA)b) hydride vapor generator (HVG)c) mercury vapor unit (MVU)

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Atomizer

IoIAtomic Vapor

l

In flame, l = length of burner head

In GFA, l = length of graphite tube

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

Flame Atomization

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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.

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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

♦ Organic solvents evaporate more rapidly than water.

♦ The desolvation leaves a dry aerosol of the molten or solid particles.

♦ This often begins in the nebulization step.

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Vaporization Of SolidsThe 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 StructureThe 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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♦ Air-C2H2

Most elements.♦ N2O- C2H2

Refractory elements e.g. Al, V, Ti etc.

♦ Ar-H2

Absorption wavelength at UV range e.g. As, Se, Zn, Pb, Cd, Sn

Selection Of FlamesFlame Temperature (oC)Ar - H2 1577Air-H2 2045Air-C2H2 2300N20-C2H2 2955

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Light Absorption Of FlamesN2O-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 mmFlame 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 do not have much affect on atomic mist distribution.

Burner height and fuel composition affect the 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-C2H2flame, 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.

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Air-Propane Burner Head

Front view

Side view

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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.

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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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♦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.

(1) Drying Step

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♦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.

(2) Ashing Step

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♦The analyte is vaporized and atomized to produce atomic vapor at around 2000-3000oC.

♦At the end of the atomization stage, the atomic vapor is rapidly diffused out of the observation zone.

(3) Atomization Step

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♦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.

(4) Cleaning Step

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Drying step

Ashing step

Atomization step

Tem

pera

ture

(o C)

Time (s)

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

0 20 35 50 54

Cleaning step (option)

GFA Heating Steps

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Graphite Tubes1) High density graphite tube2) Pyrolytic graphite tube3) Platform type graphite tube

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High density graphite tube

Pyrolytic graphite tube

Graphite Tubes

Sample Injection Port

Sample Injection Port

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Platform Type Graphite TubeSample 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

Small graphite tube

R R R

Tube length

T(°C)

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ENLARGED GRAPHITE TUBE♦Reduces background noise and hence

increases sensitivity.

Slit widthSmall graphite tube

Slit width

Enlarged graphite tube

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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 MethodTemperature of graphite tube is correlated to infrared rays emitted by graphite tube which is measured by photosensor

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Heating Methods

Tem

pera

ture

(o C)

Drying Ashing Temperature Control During AtomizationCurrent Control Method

Graphite tube deteriorates, R increases, temperature increases

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Current Control MethodDrawbacks♦The sample droplet tends to boil

off during drying step.♦The target elements are

scattered in the graphite tube during ashing step.

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Extended Temperature Control

Tem

pera

ture

(o C)

Drying Ashing

Temperature ControlDuring Atomization

Current Control Method

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

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Temperature of graphite tube (oC)

100 200 300 400 500 600

No of graphite tube being heated

Heating current of 100oC (A)

100oC

Auto Current Correction

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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 StructureNEW

OLD

Spring

Pushing force due to heating.

Pushing force due to heating.

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

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♦High sensitivity.♦Long lifetime of graphite tube.♦Best suited for continuous multi-

sample analysis.♦Reduction of running cost.

Merits of GFA Design

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Measurement Of Cr SampleGood Reproducibility

(< 2% CV)

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Long Lifetime Of Graphite TubeMeasurement 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 polymer-based arm to prevent corrosion.

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Flame/GFA Auto-Switching

Single-Body Dual Atomizer

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♦ Easy switch over between GFA and flame atomizer.

♦ High Precision x-and y-axis motorized movement.

♦ Available in model AA-6701 andAA-6800.

Dual Atomizer

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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.

Remove the furnace.

Fit the burner head.

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♦Improves productivity for multiple samples.

♦Preparation of calibration standards.♦Auto-dilution of samples.♦Addition of matrix modifiers.♦For flame microsampling and GFA.

ASC-6000/6100 Auto Sampler

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ASC-6000

ASC-6000/ASC-6100

ASC-6100

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Auto-Sampling Unit

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Mixing Mode

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

Auto-Dilution - GFA

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Flame MicrosamplingAvailable 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

Solenoid valve

closed

Sampling Port

Solenoid valve open

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Flame Microsampling

ASC-6000

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Flame Microsampling

ASC-6100

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

Auto-Dilution - Flame Microsampling

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Flame MicrosamplingParameterElement: CdWavelength: 283.3 nmSlit: 0.7nmAir-C2H2 flameC2H2：1.8L/min，Air：8L/min

auto samplerCd Conc. 1 ppm Cd H2O Total0.0 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.

♦ Suitable for environmental analysis.

As calibration curve

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HVG - Reaction

BH4- + 3H2O + H+ H3BO3 + 4H2

nascent hydrogen

3BH4- + 3H + + 4H3AsO3 4AsH3 + 3H2O + 3H3BO3

As, Bi, Sb, Se, Sn, Te Gaseous Hydride

Atomization

Flame Electrical heating cell

HVG-1

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HVG-1 - Flow Line

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HVG – Electrical Heater

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♦ Mercury Vapour Unit.♦ Mercury ion in solutions reduced by SnCl2 to

elemental mercury which vaporizes at room temperature.

MVU

♦ Suitable for environmental analysis of mercury in water.

♦ Can detect 0.1 ppb mercury

MVU-1

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MVU – Flow Line

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Typical Detection Limits (ppb) Element Flame AAS Graphite Furnace Mercury/

AAS Hydride Aluminium (Al) 30 0.01 Antimony (Sb) 30 0.2 0.1 Arsenic (As) 100 0.2 0.02 Bismuth (Bi) 20 0.1 0.02 Cadmium (Cd) 0.5 0.003 Calcium (Ca) 1 0.05 Copper (Cu) 1 0.02 Lead (Pb) 10 0.05 Manganese (Mn) 1 0.01 Mercury (Hg) 200 20 0.008 Nickel (Ni) 4 0.1 Selenium (Sn) 70 0.5 0.02 Tellurium (Te) 20 0.1 0.02 Vanadium (V) 40 0.2 Zinc (Zn) 0.8 0.001

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Flame vs GFAAtomization principle Atomized through the

heat of the flameAtomized by the heat generated when a current is passed through a resistance bulb

Sample usage rate (atomization efficiency)

Approximately 10 % Over 90 %

Amount of sample required Approximately 1 ml 5 to 50 µLShape of absorption signal Stationary signal Peak-shaped signalSensitivity Low (ppm level) High (ppb level)Reproducibility Below RSD 1.0% About RSD 2 to 5%Influence of coexisiting substances Small LargeMeasurement time Short Long

10 to 30 s per sample 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

High stabilityQuick analysis Measurement at ppm level

♦ Graphite Furnace AASMeasurement of sub-ppb levelNeed specific timings - drying, ashing, atomization processes

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

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Boosting Sensitivity In Flame AAS ♦By sample preparation

Accumulation by sample preparation♦Improving nebulization efficiency

Development of the high sensitivity nebulizer♦Improving atomization

Improvement of atomization in the flame

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Boosting Sensitivity In Flame AAS♦ Sample preparation methods

Accumulation with the volatilization of the solvent.Accumulation with solvent extraction.Accumulation by the ion exchange resin.Accumulation with the co-precipitation method which uses the chelating agent.

♦ DisadvantagesTime and time is required for sample preparation.Contamination is possible.

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Boosting Sensitivity In Flame AAS♦Improving nebulization efficiency

High sensitivity nebulizer has been mounted as a standard in Shimadzu AAS.

♦Improving atomizationResidence time of the atomized vapour is made longer.High sensitivity is achieved by Atom Booster

Sensitivity improvement of 2 or 4 times.

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Atom Booster

Atom BoosterMounting on burner head

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Atom BoosterFlame direction

Cross section of cell

Top view of cell

150 mm

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Principle Of Atom Booster

Normal flame atomization

When Atom Booster is used

Atom Booster

Volatilization of atom

Creation of atom

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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 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.

Without Booster

With Booster

As － 0.0800 －

Cd 0.0072 0.0030 2.4Cu 0.0230 0.0100 2.3Fe 0.0400 0.0300 1.3Mn 0.0250 0.0200 1.3Ni 0.0410 0.0200 2.1

Pb (217.0 nm) 0.0800 0.0200 4.0Pb (283.3 nm) 0.1900 0.0500 3.8

Sb 0.3300 0.0800 4.1Se － 0.0500 －

Zn 0.0070 0.0020 3.5

Element Sensitized Ratio

1% Absorption (ppm)

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Sensitivity Comparison

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

Without Booster With Booster Cd 0.0046 0.0018 2.6 Pb (217.0 nm) 0.0500 0.0200 2.5 Pb (283.3 nm) 0.1100 0.0500 2.2 Zn 0.0061 0.0025 2.4

Element Sensitized Ratio1% Absorption (ppm)

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With Atom Booster Without Atom Booster

0.00

0.02

0.04

0.06

0.08

0.10

0.2_1

0.2_2

0.2_3

0.2_4

0.2_5

1.0_1

1.0_2

1.0_3

1.0_4

1.0_5

0.2_1

0.2_2

0.2_3

0.2_4

0.2_5

1.0_1

1.0_2

1.0_3

1.0_4

1.0_5

Abs

orba

nce

0.2 ppm 0.2 ppm

1.0 ppm

1.0 ppm

Pb Analysis Of Oil Standard Sample

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Atom Booster - Limitations♦The sensitivity of the following elements

cannot be increased using atom booster:Alkaline (Na, K) and alkaline earths (Mg, Ca).The quartz cell reacts with silicon.Elements 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).

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Sensitivity Comparison

Shimadzu Varian ThermoCd 0.0030 0.0054 0.0040Cu 0.0100 0.0214 0.0100Fe 0.0300 0.0360 －

Pb 0.0200 0.0400 0.0300Zn 0.0020 － 0.0030

Element 1% Absorption (ppm)

♦ Product name differs in every supplierVarian: Atom ConcentratorThermo: 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.Reduces accumulation time and cost, easy and sensitive measurement is possible.

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

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Atom Booster♦P/N 206-50957-91. Consists of:

206-50937-01 Quartz tube206-51099-91 Cell holder

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(3) Optical System

ATOMIZEROPTICS

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AAS Optical System

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Single-Beam AAS

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Single-Beam Optical Systems

AA-6800/6650

AA-6701

AA-6300 GFA

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Single-Beam (AA-6800/6650)

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

♦ S : slit♦ W : window

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Electrical Double Beam

Raw Data

Baseline Drift

Corrected Data

Correction of Baseline Drift

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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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MonochromatorConsists 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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3 Monochromator Designs1) Czerny-Turner 2) Littrow3) Fastie-Ebert

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Czerny-Turner Monochromator♦ Rectifies

aberration of astigmatismand reduces stray light.

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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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Littrow Monochromator

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Fastie-Ebert Monochromator

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(5) Detector

Photomultiplier Tube

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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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Photomultiplier Tube

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(6) Signal Processing Unit

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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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ValidationThe 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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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.

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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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Operation Screen

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Can Make Changes

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Inspection Results

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Validation Program♦ Control software, operating under MS-

Windows, 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!

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Validation Program♦ Leave it to us!♦ From automatic analysis to machine

management...♦ Total planner, considering everything from

analysis to machine management, 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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INTERFERENCEIN AAS ANALYSIS &SOLUTIONS

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Interference In AAS Analysis(1) Physical Interference(2) Chemical Interference(3) Spectrophotometer Interference

a) molecular absorptionb) light scatteringc) spectral interference

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(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

Sample dispersion - measurement value fluctuates due to graphite tube temperature distribution e.g. samples in organic solvents.Sample viscosity - adherence to sampler tip causing errors in collection quantity e.g. samples such as blood or juice containing numerous organic components.

Dispensingtube

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Physical Interference♦Solutions

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

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(2) Chemical Interference♦ Causes in flame AAS

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).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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(2) Chemical Interference♦Causes in GFA AAS

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.Influence of coexisting matrices e.g. samples with high O2 content such as biological samples.Metals reacting with graphite tube to form carbides:

Metallic carbide - Ti, V, Mo, CrIntermetallic carbide - Mn, Co, NiHeteropolar carbide - Ca, BaDiamond type carbide - Si

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Chemical Interference♦Solutions

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

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Chemical Interference♦Solutions (cont)

Ionization Buffers in flameProvide an excess of electrons, to increase the free atom population of elements with low ionization potentialE.g. Cesium chloride, Cesium nitrate, Lithium chloride, Lithium nitrate, Potassium chloride, Potassium nitrate

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Chemical InterferenceUse interference suppressant to prevent

ionization in N2O/C2H2 flame.

Element Ionization Ionization Rate (%)

Energy (eV) 2000 K 3000 K

Li 5.39 2.4 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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Chemical Interference

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Use Releasing Agents in flame AASMinimize chemical interferences by combining with the interfering anions, liberating the element to be analyzedE.g. Lanthanum chloride, Lanthanum nitrate

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Use Matrix Modifier in GFAReduce the volatility of the analyte.Increase the atomization efficiency of the analyte by changing its chemical composition.Permits the use of higher charring temperatures to volatile interfering substances and improve sensitivity.Increase the volatility of the matrix.Magnesium 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

VolatileElements, e.g. + H3PO4 Cd (PO4)Cd, Pb

Decomposed at 400oC

Less volatile

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Chemical InterferenceElement Matrix Modifiers Element Matrix Modifiers

Al Mg nitrate Fe Mg nitrate or Ammonium nitareSb Ni nitrate or Pd nitrate + Mg nitrate Pb Ammonium phosphate + Mg nitrate

or Ammonium nitrateAs Ni nitrate or Pd nitrate + Mg nitrate Mn Mg nitrate or Ammonium nitrateBe Mg nitrate Ni Mg nitrate or Ammonium phosphateBi Pd nitrate + Mg nitrate Hg Pd nitrate + Mg nitrateB Ca nitrate Se Ni nitrate or Pd nitrate + Mg nitrate

Cd Ammonium phosphate + Mg nitrate Ag Pd nitrate + Mg nitrate orAmmonium phosphate

Cr Mg nitrate Te Pd nitrate + Mg nitrateCo Mg nitrate Tl Pd nitrate + Mg nitrateCu Pd nitrate + Mg nitrate or

Ammonium nitrateSn Pd nitrate + Mg nitrate or Ni nitrate

Ge Pd nitrate + Mg nitrate V Mg nitrateAu Pd nitrate + Mg nitrate Zn Mg nitrateIn Pd nitrate + Mg nitrate

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(3) Spectrophotometric Interference

♦ Causesa) molecular absorptionb) light scatteringc) spectral interference

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(a) Molecular Absorption♦ Caused by

undissociatedmolecules 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.

Alkaline metals (Li, Na, K, Rb, Cs) + Halogens (F, Cl, Br, I) = Alkali halides e.g. NaCl, KIAlkaline earth metals (Mg, Ca, Sr, Ba) + Halogens, -O, or -OH.

♦ Absorption by wings of resonance absorption lines.

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Spectral InterferenceTarget Element Spectral Line

(nm)

Interfering

Element

Spectral Line

(nm)

Al

Ca

Cd

Co

Cu

Fe

Ga

Hg

Mn

Sb

Si

Zn

308.215

422.673

228.802

252.136

324.754

271.903

403.298

253.652

403.307

217.023

250.690.

213.856

V

Ge

As

In

Eu

Pt

Mn

Co

Ga

Pb

V

Fe

308.211

422.657

228.812

252.137

324.753

271.904

403.307

253.649

403.298

216.999

250.690

213.859

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Spectrophotometric Interference♦Solution

Removal of obstructing materials by solvent extraction.Background correction by instrument.

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BACKGROUND CORRECTION

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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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(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.

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High Modulation FrequencyDeuterium 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.

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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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SELF-REVERSAL CORRECTION

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Hollow Cathode Lamp

M

MM

M

M

ArAr

Ar

Cathode

Ar

Ar

Anode

Ar + e- Ar+ + 2e-

Ar+ + M(s) M(g)

M(g) M*(g)

M(g)* M(s)

Light

e-, Ar+

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Hollow Cathode Lamp

M

MM

M

M

ArAr

Ar

Cathode

Ar

Ar

Anode

Ar + e- Ar+ + 2e-

Ar+ + M(s) M(g)

M(g) M*(g)

M*(g) M(s)

M(s)

Light

e-, Ar+

High Current

Absorbed

MM

M M

M

M

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Self-Reversal Correction♦Step I

The lamp is first run at a low current (i.e. 10mA) and its light is absorbed by the sample elements and background.

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

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Self-Reversal Correction

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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

Zn measurements in metallurgical waste water samples

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Measurement Of Zn In Fe

①

②

③

④

⑤⑥ ⑦

Atomic absorptionBackground absorption

②

③④

⑤

⑥ ⑦

Atomic absorptionBackground absorption

①

Measurement of Zn in Fe solution by the BGC-D2 methodThe absorbance of (6) is greater than (2) for the same 0.5 ppm Zn solution because of insufficient correction.

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.

When disparity arises between D2 and SR method.

Interval Width Interval Width

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Self-Reversal CorrectionZn Standard Solution

Absorbance (Abs)

Concentration (ppm)

0.10

0.05

0.20.1

BGC-D2

BGC-SR

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Zn in Fe, 1000 ppm Standard SolutionAbsorbance (Abs)

Concentration (ppm)

0.10

0.05

0.20.1

BGC-D2

BGC-SR


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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.

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Zeeman Correction♦ There are different types of Zeeman correction

depending on type of instrument configurations:

direct (magnet is directed at light source) vs inverse(magnetic field is located around the atomizer)longitude (magnetic field orientated parallel to light beam) vs transverse (magnetic field orientated perpendicular to light beam) ac (electromagnet) vs dc (permanent magnet)

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Zeeman Configurations♦The 3 most popular configurations are:

Inverse longitude ac Zeeman Inverse transverse ac ZeemanInverse transverse dc Zeeman

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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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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 ZeemanInstrumentation

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ComparisonD2 Lamp Correction Self-Reversal Method Zeeman Method

Wavelength Range 190-430 nm 190-900 nm 190-900 nm

Molecular Absorption Yes Yes Yes

CorrectionSpectral Interference No Yes Yes

CorrectionDeterioration of No Yes Yes

SensitivityLoss of Light No No Yes

IntensityInstrumental D2 Lamp No Particular Parts Polarizer and Magnet

RequirementOptical Adjustment Necessary Not Necessary Not Necessary

Atomizing Unit None None Specific

Specificity

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SAMPLEPREPARATION

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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.

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Sample Pretreatment♦ Precautions for pretreatment:

Dissolve all the elements into the same solution evenly -check with certified reference material.Ensure that elements are not lost (i.e. due to vaporization or sedimentation) in the solution - check with recovery test.Contamination from 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, sedimentation, or adsorption).Consider the effect (interference) of the reagent (e.g. acid, salt concentration) on the analysis values.

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Sample Pretreatment♦Dilution method:

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

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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:

Dry ashingWet ashing (digestion) High pressure decomposition e.g. microwave digestion.

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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.

Sample

CO2

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Dry AshingDrying

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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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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Wet AshingClean, readily oxidized sample

HNO3- H2SO4 HNO3-HCl

HNO3- HClO4 or HNO3- HClO4 -HF

Difficult-to-oxidized organicsamples

Samples containing -OH, oxide, sulfide, phosphate

HNO3

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Wet Ashing – H2SO4 & H2O2Sample

Oxidation

Remove H2O2

Digestion & Oxidation

H2SO4

H2O2

Boiling

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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.

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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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).

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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 decompositionSealed system decomposition, little volatilization of low boiling point elements, quick decomposition times.Little contamination from the operating environment & reagent; little acid is used.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:

Decomposition takes short time.No volatilization during decomposition thanks to sealed system.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 smallamounts have been collected.

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Alkaline Fusion♦ The sample is fused with

alkaline flux by heating to a high temperature e.g. 1000oC)

♦ For metallic compounds and ceramics, high molecular weight and complex samples e.g polymers, sand, etc.

♦ The sample will have a high salt concentration –interference and contamination have to be taken into account.

Sample

Fusion

Na2CO3

Acid dissolution

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Total Content

Dilution, Elution

Purified water, solvents, etc.

Wet Decomposition

Hydrochloric acid, nitric acid,

etc.

Dry/Wet Decomposition

High-pressure Decomposition

Nitric acid, sulfuric acid, etc.

Alkali Fusion

Wet/High-pressure Decomposition

Hydrofluoric acid, nitric acid, etc.

Sample Pretreatment

Simplewater-solubleions

Simple soluble metals & compounds

Carbonates, oxides, etc.

Inorganic compoundswith low solubility

Sulfides, oxides,silicates, etc

Organiccompounds

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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 ReagentsSodium diethyl dithiocarbamic acid (NaDDC)Ammonium pyrrolidine dithiocarbamicacid (APDC)

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Solvent Extraction Method

Chelating agents Elements

Metal-chelates

Solvent Extraction

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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).

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Sample Acquistion

(Protect Nebulizer)Filtering

Residuals

Decomposition

Measurements

Filtration

Filtered solution

Solvent extractionConcentrationMeasurement

Measurement Measurement Concentration

Measurement

Workflow - Example 1

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Sample

Hydrolysis

Filtration

Residual

Fusion

Dissolution

Measurement

Filter solution

Measurement

Melting agent

Acid

Workflow - Example 2

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Thank you!

Lò Graphite -Quang phổ hấp thu nguyên tử

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