ATOMIC ABSORPTION SPECTROSCOPY (AAS)

SPEKTRUM GELOMBANG ELEKTROMAGNETIK

Elements detectable by atomic absorption are highlighted in pink in this periodic table

- Atomic-absorption spectroscopy quantifies the absorption of ground state atoms in the gaseous state . The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels. The analyte concentration is determined from the amount of absorption. Concentration measurements are usually determined from a working curve after calibrating the instrument with standards of known concentration. - Atomic absorption is a very common technique for detecting metals and metalloids in environmental samples.

AAS

TEORI

TEORIAAS : salah satu metode yang paling umum untuk analisis logam dan beberapa semilogam (metalloids)Logam : Fe, Pb, Cr, dll.Metalloids : Sb, As, Se, dan Te Metode analisis kuantitatif yang didasarkan pada penyerapan/absorpsi radiasi oleh atomAkibat absorpsi :Transisi elektron dari ground state ke excited state

Transisi Energi yang diserap sesuai dengan perbedaan energi transisi dari GS ke ES

e e AEhvhv++E = E1 E0 = hc / E1 - excited stateE0 ground stateh Plancks constantc velocity of light - wavelength

E3(Excited state)E2(Excited state)E1(Excited state)Eo(Ground state)AbsorptionEmissionResonance LinesMost Intense Line3 Absorption Lines6 Emission linesAtomic Absorption and Emission LinesE = E1 - E0 = h = hc/E

*Both methods are used to determine the concentration of an element in solution.Both methods use a standard curve.Difference between UV and IR spectroscopy is that sample must be atomised.Sample may be atomised by:(1) A flame(2) Electrically heated furnace(3) A PlasmaUV-Vis vs AAS

*SensitivityAtomic spectroscopy is very sensitive for most elements.Concentrations at the ppm level may be routinely determined using flame atomisation.Using electrothermal atomisation, concentrations at the ppb may be determined.1 ppm = 10-6g/g or 1g/g

INSTRUMENTASI

Atomic Absorption Spectrophotometer

The Atomic Absorption SpectrometerAtomic absorption spectrometers have 4 principal components1 - A light source ( usually a hollow cathode lamp )2 An atom cell ( atomizer )3 - A monochromator4 - A detector , and read out device .

Skema Kerja AASLampBurnermonochromatorslitdetectormeter

Skema Cara Kerja AAS

The Flame Atomization Process[M+,X-]aq[M+,X-]aqnebulizationsolutionmist[MX]solidvaporizationdesolvation[MX]gasatomization[M0]gasLight with specific IoIaIt

How can we obtain the data?The intensity of the light coming through the cathode lamp is measuredThe light can then be absorbed by the atoms from the sample that has been vaporized in the flame.This wavelength can then promote the electrons to a higher energy level = excited stateThe intensity of the light is then again measured and compared to the first result. = absorbanceThe higher the concentration of the metal that is being observe in the sample the greater the absorbance.

Fungsi masing-masing komponen alat1. Light source It is designed to emit the atomic spectrum of a particular element. Specific lamps are selected according to the element to be determined. The hollow cathode lamp (HCL) or electrode Discharge Lamps (EDL) are widely used.

Hollow Cathode Lamp

The light source is usually a hollow cathode lamp of the element that is being measured. It contains a tungsten anode and a hollow cylindrical cathode made of the element to be determined. These are sealed in a glass tube filled with an inert gas (neon or argon ). Each element has its own unique lamp which must be used for that analysis . Quartz windowPyrex bodyAnodeCathode

Hollow Cathode LampThe cathode of the hollow cathode lamp (HCL) contains the element being analysed.Therefore the atomic radiation emitted by the HCL has the same frequency as that absorbed by the analyte atoms in the flame or furnace.The linewidth from the HCL is relatively narrow (compared to linewidths of atoms in the flame or furnace) because of low pressure in lamp and lower temperature in lamp.Thus the linewidth from the HCL is nearly monochromatic (vs sample).

Scheme of a hollow cathode lamp

*Apply sufficiently high voltage between the cathode and the anode:(1) Ionization of the filler gas: Ne + e- = Ne+ + 2e-(2) Sputtering of the cathode element (M):M(s) + Ne+ = M(g) + Ne(3) Excitation of the cathode element (M) M(g) + Ne+ = M*(g) + Ne(4) Emission of radiation M*(g) (M(g) + h

Constructed from a sealed quartz tube containing a few torr of an inert gas such as argon and a small quantity of the metal of interest (or its salt).The lamp does not contain an electrode but instead is energized by an intense field of radio-frequency or microwave radiation. Radiant intensities usually one or two orders of magnitude greater than the normal HCLs.The main drawbacks: their performance does not appear to be as reliable as that of the HCL lamps (signal instability with time) and they are only commercially available for some elements. Electrodeless Discharge Lamps(EDL)

Electrodeless Discharge Lamps(EDL)

Proses atomisasi

Sample cell- Tungku pembakar2. Sample cell Where an atomic sample vapor is generated in the light beam from the source. Nebulizer : Suck up liquid sample at a controlled rate Create a fine aerosol for introduction into the flame Mix the aerosol and fuel and oxidant thoroughly for introduction into the flame

Nebulasi

Nebulizer - burner

Nebuliser - burnerTo convert the test solution to gaseous atomsNebuliser --- to produce a mist or aerosol of the test solutionBurner head --- The flame path is about 10 12 cmVaporising chamber --- Fine mist is mixed with the fuel gas and the carrier gas Larger droplets of liquid fall out from the gas stream and discharged to waste

Fuel Flow rate

Oxdnt. Flow rate

Burner height

Proses atomisasi : 2 cara Dengan nyala : Flame api, PlasmaTanpa nyala ( Flameless) :HidridaPembentukan uap dingin (Cold Vapor-generation)Tungku grafit

Atomisasi

Flame Create atoms (the elemental form) of the element of interest Fe0, Cu0, Zn0, etc.

Temperature nyalaTergantung pada kombinasi oksidan dan bahan bakar Bahan bakar : asetilen, gas alam, hidrogenOksidan : udara, N2ODestroy any analyte ions and breakdown complexes

Types of Flames Used in Atomic Spectroscopy

FLAMESRich in free atoms

Various flame atomization techniques

*Atomization occurs in an electrically heated graphite tubeThe graphite tube is flushed with an inert gas (Ar) to prevent the formation of (non-absorbing) metal oxides

Electrothermal or Graphite Furnace Atomizergraphite tube

Grafit furnace atau electro thermal atomizer (ETA) :Penghantar panas listrik : batang grafit C atau Ta, yang dialiri gas inert untuk mengusir udara yang menyebabkan oksidasi/ pembakaranSampel dalam l diuapkan di atas permukaan furnacePemanasan furnace dimulai 100oC dengan cara mengalirkan arus listrik : penguapan pelarut atau pengeringan sampel padatSuhu dinaikkan sampai 700-1000oC sehingga sampel terbentuk abu. kemudian suhu dinaikkan menjadi 2000-3000 dengan menaikkan arus sampai 100mA terjadi atomisasi. Sisa pembakaran dihembus dengan gas Ar

*Electrothermal Atomisation Graphite Furnace Sample holder consists of a graphite tube.Tube is heated electricallyBeam of light passes through the tube.Offers greater sensitivity than flames.Uses smaller volume of sampletypically 5 - 50 l (0.005 - 0.05 ml).All of sample is atomised in the graphite tube.

Schematic Diagram of a Graphite Furnace

Tempat Sampel

*Stages in a Graphite FurnaceTypical conditions for Fe:Drying stage:125o for 20 secAshing stage1200o for 60 secAtomisation2700o for 10 sec

Requires high level of operator skill.Method development difficult.

Steps in GF atomizationDrying AshingAtomization

*Advantages and Disadvantages of Flame AASAdvantagesequipment relatively cheapeasy to use (training easy compared to furnace)good precisionhigh sample throughputrelatively facile method developmentcheap to runDisadvantageslack of sensitivity (compared to furnace)problems with refractory elementsrequire large sample sizesample must be in solution

Advantages and Disadvantages of Electrothermal AtomisationAdvantagesvery sensitive for many elementssmall sample sizeDisadvantagespoor precisionlong cycle times means a low sample throughputexpensive to purchase and run (argon, tubes)requires background correctionmethod development lengthy and complicatedrequires a high degree of operator skill (compared to flame AAS)

3- MonochromatorsThis is a very important part in an AA spectrometer. It is used to separate out all of the thousands of lines. Without a good monochromator, detection limits are severely compromised.

A monochromator is used to select the specific wavelength of light which is absorbed by the sample, and to exclude other wavelengths. The selection of the specific light allows the determination of the selected element in the presence of others.

4 - Detector and Read out Device The light selected by the monochromator is directed onto a detector that is typically a photomultiplier tube , whose function is to convert the light signal into an electrical signal proportional to the light intensity.

The processing of electrical signal is fulfilled by a signal amplifier . The signal could be displayed for readout , or further fed into a data station for printout by the requested format.

ANALISIS KUANTITATIF

Dasar Analisis KuantitatifHukum Beer :Jika Io dilewatkan larutan dengan konsentrasi C maka intensitas berkurang menjadi It yang sebanding dengan C Io/It = k. CHukum Lambert-BeerJika Io dilewatkan larutan setebal b maka intensitas berkurang menjadi It yang sebanding dengan b Io/It = k.b

Hukum Lambert -BeerIo/It = e k b C

ln Io/It = k.b.Clog Io/It = k/2,303 .b C = abC

It/Io x 100 % = T %log Io/It = log I/T = Ajadi A = abC = b. C

Validitas A = a b CUntuk absorpsiUntuk konsentrasi yang relatif rendahKonsentrasi besar : terjadi interaksi antara analit sehingga mengurangi absorpsi radiasi penyimpanganKesalahan minimal :A = 0,44 atau 0.2-0.8C sangat kecil A terlalu kecil It dan Io hampir sama kesalahan besar

Aplikasi hukum Lambert BeerMembandingkan A standar dengan A sampel :Standar tunggalDeret standar Kurva standarAdisi standar

Standar tunggal1. Larutan standar Pt 5 ppm T = 65%. Sampel limbah 10 ml diencerkan menjadi 50 ml T = 45%Tentukan kadar Pt dalam limbah cair = ? mg/L

2. Tanah galian yang mengandung logam emas, 2 gram dilarutkan menjadi 100 ml. Absorbansi = 0,54Larutan standar 10 ppm A =0,24Tentukan berapa % Au dalam sampel ?

Kurva StandarKonsentrasi lar. standarIntensitas

Contoh Lar.stand Ag A2 0,124 0,216 0,338 0,4210 0,51 Jika 1 g sampel uang logam dilarutkan menjadi100ml. Diambil 5ml diencerkan menjadi 50ml, A = 0,35. Tentukan kadar (%) Ag dalam sampel

Adisi standarUntuk mengatasi kesalahan matriks menyamakan keadaan larutan sampel dengan lar. StandarCara : mencampurkan sampel dengan standar

Volume sampel (mL)Volume larutan standar Cu 10 ppm (mL)Absorbansi1000,20110100,29110200,37810300,46710400,554

Persiapan sampelHarus berupa larutan jernihPadatCair Larutan jernihAASGas Destruksi Penyaringan/pengasamanPenyerapanpelarutan

Gangguan dalam Analisis

Gangguan dalam AASSpektrum : Spektra analit overlap dengan spektra pengganggu, karena spektrum absorpsi pengganggu berdekatan dengan spektrum absorpsi analit (

KimiaAdanya reaksi kimia : pembentukan senyawa dengan volatilitas tinggi atau rendahIonisasi dalam nyalaAsosiasi atau disosiasiMatriksViskositas larutan standar tidak sama dengan analit

Cara mengatasi Gangguan KimiaReaksi kimia : Pembentukan senyawa yang tidak volatilMenggunakan suhu nyala yang lebih tinggiDengan penambahan Masking agent /protective chelationDengan penambahan Releasing agent

*ExamplesDetermination of calcium in the presence of sulfate or phosphate (e.g. in natural waters) 3Ca2+ + 2PO43- = Ca3(PO4)2 (stable compound)Release agent Add 1000 ppm of LaCl32LaCl3 + Ca3(PO4)2 = 3CaCl2 + 2La(PO4) CaCl2 readily dissociatesProtective chelationCa3(PO4)2+3EDTA = 3Ca(EDTA) + 2PO43-Ca(EDTA) dissociates readily.

*Ionisation Interference M(g) M+(g) + e-A problem in the analysis of alkali metal ions at low flame temperatures and other elements at higher temperatures. Because alkali metals have the lowest ionisation potentials, they are most extensively ionised in flames.At 2450 K and a pressure of 0.1 Pa, sodium is 5% ionised.Potassium is 33% ionised under the same conditions.Ionised atoms have energy levels which are different to the parent atomstherefore the analytical signal is reduced.

SolutionAdd an ionisation suppressor

Add an easily ionised element such as Cs.Add 1000 ppm of CsCl when analysing Na or K.

Cs is more readily ionised than either Na or K.This produces a high concentration of electrons in the flame.

Matrix effectsThe amount of sample reaching the flame is dependent on the physical properties of the solution:viscositysurface tensiondensitysolvent vapour pressure.To avoid differences in the amount of sample and standard reaching the flame, it is necessary that the physical properties of both be matched as closely as possible.Example:Analysis of blood ----> Addition Standard

*Non-Atomic AbsorptionNon-atomic absorption is caused by molecular absorption or light scattering by solid particles in the flame.The absorption measurement obtained with a hollow cathode lamp is the sum of the atomic absorption and the non-atomic absorption. The interference is corrected for by making a simultaneous measurement of the non-atomic absorption using a continuum source (usually deuterium)This problem is overcome by increasing the flame temperaturethis is called background correction

Background Correction

Metode dalam AAS

Pembentukan uap dingin :Khusus untuk Hg

Reduksi dengan SnCl2 :Hg2+ + Sn2+ Hg0 atom (uap) +Sn4+ Hg0 + hv absorpsi

Sensitivitas tinggi (< 1ppb-ppt)Uap Hg berbahaya

Cold vapour techniqueHg2+ + Sn2+ = Hg + Sn (IV)

Hydride generation methodsFor arsenic (As), antimony (Te) and selenium (Se)As (V) AsH3As0(gas) + H2NaBH4(sol)heatin flame[H+]

Pembentukan senyawa hidridaUntuk unsur yang suhu atomisasinya tinggi maupun yang sangat rendah : As, Bi, Sb, Se, Te dan Ge.Unsur diubah menjadi senyawa hidrida yang volatil :Reduksi unsur dengan NaBH4 dalam asam atau basa uap AsH3, BiH3, dstUap logam hidrida dibawa oleh gas inert menuju sel atomisasi (nyala api atau filamen listrik) atomisasi AsH3 AsoAso + hv absorpsi

Sensitivity and detection limit(ng/mL)

Advantages and disadvantagesHigh sensitivity [10-10g (flame), 10-14g (non-flame)]Good accuracy (Relative error 0.1 ~ 0.5 % )High selectivityWidely usedA resonance line source is required for each element to be determined

Contoh-contoh

Atomic Emission Spectroscopy

Inductively Coupled PlasmaAtomic Emission Spectroscopy

Atomic Emission TheoryAtomic emission spectroscopy (AES or OES) uses quantitative measurement of the optical emission from excited atoms to determine analyte concentration

Analyte atoms in solution are aspirated into the excitation region where they are desolvated, vaporized, and atomised by a plasma

ICP AES Electrons of an atom absorb energy and jump to higher energy levels

When they return to normal states, they emit characteristic photons of energy

By isolating these photon wavelengths, we can determine the types and concentrations of the elements present.

Atomic Emission Theory

ExcitationElectrons can be in their ground state (unexcited) or enter one of the upper level orbitals when energy is applied to them. This is the excited state

_1082533585.doc

Excited State

Ground State

E

Relaxation

Excitation

Atomic EmissionPhotonExcited StateGround State+ hvA photon of light is emitted when an electron falls from its excited state to its ground state

Element WavelengthsEach element has a unique set of wavelengths that it can emit

180nm800nm400nm

12345

(

(

(

(

(

Atomic Emission explainedAtomic Emission the wavelength regionsLower wavelengths are shorter and have more energy, higher wavelengths e.g. in the Visible region, are longer and have less energy

Effect of Temperature on EmissionWavelength increasing ->2000 k3000 k5000 kCaNaLiKCaNaLiKKLiNaCaBaBaCuMgMgCuAsPbMn 200 300 400 600 800

Emission sources

Flames

Direct Current Plasmas (DCP)

Inductively Coupled Plasmas (ICP)

A plasma is an electrical conducting gaseous mixture containing a significant concentration of cations and electrons. (The concentrations of the two are such that the net charge approaches zero). In the argon plasma frequently employed for emission analyses, argon ions and electrons are the principle conducting species, although cations from the sample will also be present in lesser amounts. PLASMA

Plasma has 2 characteristics:i- can conduct electricityII- affected by magnetic fields

Plasma is highly energetic ionized gases usually inert, recently reactive oxygen is used.

Other plasmas include direct current plasma (DCP) and microwave induced plasma (MIP)

Plasmas

ICP-AESInductively coupled plasmas are at least 2X as hot as flames or furnaces.The Ar plasma is the result of the flow of Ar ions in a very strong, localized radio field.6000-10000 K are common plasma temperatures.Hot enough to excite most elements so they emit light.Hot enough to prevent the formation of most interferences, break down oxides (REEs) and eliminate most molecular spectral interferences.

Plasma AdvantagesHigh Temperature allows for full dissociation of sample componentsArgon is Inert non reactive with sampleLinearity analysis of samples from ppb to ppm range in the same methodMatrix tolerance robust and flexible design with Duo and Radial options

Instrument ComponentsComputer and SoftwareSample IntroductionEnergy SourceSpectrometerDetectorElectronics

Sample IntroductionThe sample solution cannot be put into the energy source directly. The solution must first be converted to an aerosol.The function of the sample introduction system is to produce a steady aerosol of very fine droplets.Instrument Components

Sample IntroductionThere are three basic parts to the sample introduction system. the Peristaltic pump draws up sample solution and delivers it to the Nebulizer which converts the solution to an aerosol that is sent to the Spray chamber which filters out the large, uneven droplets from the aerosol.Instrument Components

Energy SourceThe sample aerosol is directed into the center of the plasma. The energy of the plasma is transferred to the aerosol.The main function of the energy source is to get atoms sufficiently energized such that they emit light.Instrument Components= plasma

Energy SourceThere are three basic parts to the energy source. the Radio frequency generator which generates an oscillating electo-magnetic field at a frequency of 27.12 million cycles per second. This radiation is directed to the Load coil which delivers the radiation to the Torch which has argon flowing through it which will form a plasma in the RF field.Instrument Components

Radial or Axial ConfigurationRadial design Robust, fewer interferences PetrochemicalMetallurgy

Axial design best sensitivity, lowest detection limits EnvironmentalChemical

Duo viewingAxial view plasma looks down the central channel of the plasma, this provides the best sensitivity and detection limitsDUO this is an axially configured plasma that also allows for radial view through a hole in the side of the axial torch

Dual View OpticsAxial viewRadial view

Instrument ComponentsSpectrometerOnce the atoms in a sample have been energized by the plasma, they will emit light at specific wavelengths. No two elements will emit light at the same wavelengths.The function of the spectrometer is to diffract the white light from the plasma into wavelengths.

Simultaneous Optics Echelle Spectrometer

Instrument ComponentsSpectrometerThere are several types of spectrometers used for ICP. Regardless of type, all of them use a diffraction grating.For the iCAP, an echelle spectrometer is used. The components in this spectrometer are shown at left.

Instrument ComponentsDetectorNow that there are individual wavelengths, their intensities can be measured using a detector. The intensity of a given wavelength is proportional to the concentration of the element. The function of the detector is to measure the intensity of the wavelengths.

What you getFull, continuous wavelength coverage; never miss an analyte

Power and flexibilityRapid qualitative analysisAbility to analyze for elements in the future without rerunning samplesFingerprintingMatrix or spectral subtraction

Instrument ComponentsElectronicsThe output from the detector is processed by a set of electronics. The electronics control the detector as well as collect the readings from the pixelsThe function of the electronics is to measure and process the output of the detector.

ICP Basics ICP PerformanceTypical analysis time for ICP is ~2-3 minutes. This includes flush time, multiple repeats, printing, etc. (Analysis time is independent of the number of elements being determined)

Typical precision, amongst repeats within an analysis, is ~0.5%

Typical detection limits are ~ 1-10 parts per billion

Atomic Absorption VS Emission Spectroscopy Absorption

- Measure trace metal concentrations in complex matrices .

- Atomic absorption depends upon the number of ground state atoms . Emission

- Measure trace metal concentrations in complex matrices .

- Atomic emission depends upon the number of excited atoms .

- It measures the radiation absorbed by the ground state atoms. - Presence of a light source ( HCL ) .

- The temperature in the atomizer is adjusted to atomize the analyte atoms in the ground state only.

- It measures the radiation emitted by the excited atoms .- Absence of the light source .

- The temperature in the atomizer is big enough to atomize the analyte atoms and excite them to a higher energy level.

**********Libraries*In the case of commercially available ICPs, the ionized gas is argon. Helium plasmas are possible but for cost and performance reasons, argon is preferred. It is possible to form plasmas using molecular gases O2, N2, CO2 but these require huge amounts of energy and can react chemically with the analytes being measured so inert gases are preferred.Libraries*In the case of commercially available ICPs, the ionized gas is argon. Helium plasmas are possible but for cost and performance reasons, argon is preferred. It is possible to form plasmas using molecular gases O2, N2, CO2 but these require huge amounts of energy and can react chemically with the analytes being measured so inert gases are preferred.*Libraries**The iCAP 6000 is echelle spectrometer. A shell spectrometer utilizes a prism and a grating working together To split the spectrum of byte order and wavelengths and end the entire spectrum onto the square or rectangular detector.This impulse cannot take on this alliance demonstrates the design of the echelle spectrometer.In the bottom right of the slide you can see the source which in this case is the ICP . Excited atoms In the ICP emit light at characteristic wavelengths which are focused into the spectrometer.The limited lights passes through a prism and is reflected off a grating to produce the echelle spectrum.As I mentioned in the previous slight the echelle spectrum is a square or rectangular shape and can be captured using a detector that matches exactly the shape of the spectrum.By adopting a national spectrometer design we can use a custom designed solid state detector to analyze the signal .

Libraries*Libraries*Libraries*