Atomic Absorption Spectrophotometry
yp'ume 13Number lHORNCASTLE : ATOMIC ABSORPTION SPECTROPHOTOMETRYAtomicAbsorptionSpectro photometryD. C. J. H O R N C A S T L EM . S c , Ph.D., F . R . I . C , F.R.S.H.SummaryHISTORICALLY flame emission spectroscopyWas developed first. Routine analysis showedthe advantage of measuring absorption overemission for m a n y metals. Instrumentation" equirements a r e : —I · Pressure regulators a n d flowmeters withthe sources of gases;a. Atomizer;3- Burner;4· Optical system;5· Detector.In addition, a n energy source, e.g., ahollow cathode lamp, is needed.Essentially the technique involved is thesame as absorbance in a solution but taken"*to a flame. T h e ground state atoms are pected to pick u p the correct energy. A fop in intensity is measured.Acetylene/air a n d acetylene/nitrous oxide re widely used now as flames. A complextheory of flames is discussed and conceptualdifficultiesare mentioned.Interferenceeffects, e.g., c o m p o u n d formation a n d ioniza tion, are cited. Parameters affecting thesignal are explored mathematically.Sensitivities a n d detection limits are com pared in respect of flame emission a n d atomicabsorption for the elements of interest. Ways? ;· D- G. J. Horncastle, South-Western Forensicscience Laboratory, 37 Julian Road, Bristol, BS9 iJY.of improving performance are presented.Awareness of contamination problems isimportant.For forensic applications and problems,absolute detection limits are lower withatomic absorption than in photometry for themajority of the listed elements. A m o n g otheradvantages are specificity, several elementscan be determined in one sample and one canoperate on smaller samples than in somechemical methods, m a n y elements can besurveyed with the one instrument, and thereis freedom from time elapsing during colourdevelopment and drying of precipitates. Allthis is at relatively low cost, althoughsophisticated apparatus and elaborate access ories can be expensive.More than 50 per cent of instrumentsbought have been applied to biochemical a n dagricultural projects. Versatility is evidentfrom assays of the m a n y trace elementspresent in all kinds of water.A m o n g disadvantages are failures withsome lamps, too much trouble with thenebulizer, and the scarcity of informationregarding the determination of major con stituents. Suitable precision, adequate sensi tivity, acceptable drift, allowable blank, a n da satisfactory calibration curve are necessaryfor best accuracy.Post-mortem urine samples were examinedfor a variety of elements and in the case of
MEDICINE, SCIENCE, AND THE LAWlead poisonings, blood and ' wet oxidized 'tissue were analysed.Reproducibility and difficulties of samplingand technique were compared using the threebasic types of instrument available.For m a x i m u m sensitivity and best detec tion limits the double-beam instrument ispreferred. L a m p , detector, and electronicdrift are eliminated and its stability issuperior.INTRODUCTIONHistorically flame emission spectroscopywas developed first with the flame acting asthe emission source. M a n y emission lines canalso be studied in ' absorption spectra ' ofwhich the well-known Fraunhofer lines of thesun's spectrum a r e a n example. If continuousradiation is passed through the vapour of anelement, black lines, showing that light of thecorresponding wavelength has been absorbed,can be observed spectroscopically.Thepositions of these absorption lines correspondexactly with those of the visible lines of theemission spectrum of the same element.Frequently more lines are observed inemission than in absorption, a n d so the lattertype are often used where a simplification isdesirable.T h e potential of spectrochemical analysiswas realized with the pioneer work byBunsen and KirchofT in i860 on the atomicspectra of the solar atmosphere. Routineanalysis developed by Walsh in 1953 showedthe advantage of measuring absorption overemission for m a n y metals (Walsh, 1955).INSTRUMENTATIONUnits required for flame emission spectro scopy are as follows: (i) Pressure regulatorsand flowmeters with the sources of cuttinga n d oxidizing gases; (2) Atomizer for liquidsand solids; (3) Burner; (4) Optical system foremitted light; a n d (5) Detector a n d ' read out ' device.In respect of (i) needle valves are essentialand flowmeters are required for monitoringpurposes. If compressed air is used, thencylinders are exhausted quickly a n d for con tinuous use p u m p i n g assemblies are pre ferred.Medicine Sei. U w1973, Jan.T h e description of (2) as a n atomizer isdeceptive because the sample is sent into theflame at a stable a n d reproducible rate. T h eatomizer should not be attacked by corro sives, must be rugged a n d easy to clean. Thisis a great deal to expect. Basically, twodesigns are available. O n e introduces aspray in a spray chamber separate from theflame and part of the spray is carried ordriven into the flame. T h e other presents thesolution directly to the flame, i.e., the burnerand atomizer are one, and is known as a totalconsumption burner. This is something of amisnomer; although everything is sprayed,all the solution is not, in fact, used.T h e first type (Fig. i A, B) is fitted with twofine capillaries sealed into a glass envelope(which makes for easy cleaning) and aVenturi eflfect is achieved to aspirate. A finemist is carried to the burner. Details can bevaried as shown. Normally the consumptionof the solution is from i to i o ml. per minuteand 10 per cent of this reaches the flame. Iforganic solvents are present, the problem ofan explosion hazard arises with a premixburner utilizing oxygen a n d acetylene.Therefore an inert gas such as nitrogen orargon is substituted when an organic matrixis to be sprayed.T h e second type has a stainless-steel,palladium-tipped capillary within two con centric cones {Fig. iC) and is known as aBeckmann burner. Often so much solutiongoes into the flame that it could be cooledsome 300 C. Untouched solution comes oflfbut this is useful for organic liquids in thatthere is no danger of explosion as long asgases are flowing out of the burner, e.g., pureketones can be used with acetylene, air,hydrogen, and oxygen. T h e sound of theacetylene/oxygen flame is almost unbearable— a n assault on the nerves and very tiring—whereas the sounds of nitrogen or inert mix ture flames are tolerable. Organic solventswill cause an elevation of the flame tempera ture.Before the advent of atomic absorptionspectroscopy, there was a growing fieldinvolving the chelation of the metal anddetermining it in an organic spray, e.g.,aluminium was chelated with 8-hydroxy
Volume 13Number 1HORNCASTLE: ATOMIC ABSORPTION SPECTROPHOTOMETRYquinoline a n d determined in methylisobutyl»betone ( M I B K ) .Solids—though the method is not usedniuch for them—can be used directly, but anin the 300 to 350 n m .for transition metals,achieved are not' noisier ' acetylene is(mμ) range, of interestand the temperaturesvery different whenpresent.SolutionCompressed airBurnerSolutionTo flameWasteWasteFuel gasOxidizing gasSolutionFio. I , — T y p e s of atomizer used in flame emission spectroscopy. A, B, T y p e with two fine capillariesfealed into a glass envelope. C, T y p e with a stainlcss-stccl palladium-tipped capillary known as a Beckmann"Urner. P a n d e d capillary is then needed. Slurriesare made with glycerol or glycerine. Refrac tories of the tube will wear eventually. A ide-bore capillary is generally suitable forsolids and a waste exit is, of course, not" equired.When considering the burner, the aim has c n to obtain bigger, better, a n d hotternames. Initially for alkali metal studies af i x t u r e of town gas and air was used.Further developments may be appreciated" om Table I.For the hydrogen and oxygen mixture the mission spectrum has a low ' b a c k g r o u n d 'Table I.—ToSHOW THEAIRT Y P E OF F L A M EPropaneButaneHydrogenAcetyleneT E M P E R A T O R E OF FLAMESANDINOXYGENAIR1925"c.1400 c.2100 c.2200 c.If organic solvents aresimpler flame, nothing isthese solvents are burnt.Problems arising withinclude the depressant effectOXYGEN2400 2500 2780 3050 C.c.c.c.used with thegained becauseflame emissionof calcium with
MEDICINE, SCIENCE, AND THE LAWphosphate. T h e latter interferes. Similarly,aluminium and phosphate upsetflameemission.Compounds formed require ahotter flame to break them u p . Such de composition has been accomplished by thecyanogen/oxygenflamewhichreaches4550 C. but cyanogen (CjNj), marketed inthe U.S.A., is expensive.Another good flame, developed in Ger m a n y , is thehydrogen/perchlorofluoridecombination which burns to about 3000 C.Perchlorofluoride (CIO3F) is a stable gas,a n d is a liquid under pressure at roomtemperature. It may be compared with thehydrogen/oxygen mix to which it is analogousas regards the small ' background ' obtained.It is extremely efficient for use with smalltraces of magnesium, as instead of mag nesium oxide formation it produces mag nesium fluoride which is then broken down.Little information has yet been released onhydrogen/fluorine flames which attain tem peratures of 4400 C. Here oxygen is keptaway from the samples and no oxides needexist. Transition metal fluorides are muchless stable thermally and hence good emissionlines are obtained.A modern flame at 3200 C. is acetylene/nitrous oxide which has an impressiveappearance. It has a very reactive red' f e a t h e r ' zone and if measurements arem a d e just above this one obtains supremesensitivity. Although this flame is little usedas a n emission source, it has wide applicationin atomic absorption work. T h e burner headmust be of the slotted type (3 in. by Ο Ό 1 5 in.;longer steel would warp) and not of the' Meker ' variety (i.e., round holes) althoughgood quality stainless-steel (J-in. thick) ishard to drill and cut. Acetylene-rich flamescause warping and previously water-suppliesparallel to the slot were used to prevent thisdistortion. ' Sooting up ' is another problemwhich arises when using the hydrocarbona n d so the burner head is milled out belowthe exit slot to reduce any clogging. T oignite, the air/acetylene is introduced first,then the air is turned down, and the nitrousoxide brought up.A similar flame is the hydrogen/nitrousoxide,'which has a quiet, low ' b a c k g r o u n d 'Medicine Sei. L«w1973, Jan.character (cf hydrogen/oxygen) at 600 C.but will burn at a slot or ' Meker '-typeburner.It is most suitable for atomicfluorescence spectroscopy (q.v.).T h e theory of flames is complicated a n d isa judicious blend of inspiration, imagination,and perspiration. All that is really known,definitely, is that a signal emerges. A solu tion of the metal reaches the flame where thesolvent evaporates a n d the salt is left as agranule which is decomposed a n d vaporizedto produce atoms or simple molecules.Ideally all the gaseous molecules are dis sociated eventually to give neutral atomswhich are potential sources of emission, i.e.,ground state entities. Conceptually there aredifficulties in such a treatment and obscur ities such as the absence of a plausible mech anism for the appearance of neutral sodiumand chlorine atoms from the ionic lattice ofsodium chloride. Atomic absorption systemsare shown in Fig. 2.As metal atoms are formed, some unitewith atoms or radicals already in the flameand if these compounds are sufficiently stablethere is eflfectively a loss of the atoms ofinterest, i.e., the beginning of a matrixeffect.T h e vapour of the neutral free metal atomsthen responds to the thermal energy of theflamea n d the atoms become excited.Regretfully, at the same time, ionizationoccurs too. (Electrons are removed.)Finally, the atom excited from the groundstate drops back thus emitting energy whichis observed. T h e energy lost or not seen isthat of the electron not concerned with theatom, i.e., freed electrons. Neither a matrixeffect nor the ionization is wanted becausethe ground state atomic population is therebydiminished. This is true for atomic emissionand absorption spectroscopy. In the ffame notall the lines of the arc or complete spectra arepresent. O n l y predominant lines are visibleand the flame spectrum is simplified. A prob lem in both techniques is that of excited oxidemolecules, if oxygen is burned, since there arem a n y modes to the ground state and b a n dspectra result. C o m p a r e , for instance, thegood sharp atomic line of calcium with theb a n d due to the very stable b a r i u m oxide.
Volume 13Number 1HORNCASTLE : ATOMIC ABSORPTION SPECTROPHOTOMETRYFor the optics, monochromators are usedfor separating signals. Generally there is notmuch light out of the flame. Intensity issmall. Hence high light-gathering power(Vs) Vé-5 gives a photographic comparison)is the aim. Solution work ('/ιβ, V20) demandsnarrow slits and good resolution {Fig. 3).Filters are rarely used. Depending on themachine and its age prisms or gratings m a ybe employed.Lampbut this meant concentrated solutions a n dblockages of jets. Atomic absorption methodswere designed to overcome such troubles asfar as possible.Essentially this technique is the same asabsorbance in a solution but taken into aflame.T h e instrument principle in theatomic absorption process is given in Fig. 4.T h e ground state atoms are expected to picku p the correct energy. A d r o p in intensity isFlameMonochromatorDetector andd.c. amplifierFlameMonochromatorD e t e c t o r anda.c. amplifierChopperLamp\Λ( 100cycles per second)ReferenceOl'Detector andLampFlameSamplei\Monochromatora.c. electrometerBeam recombining (50 per cent m i r r o r )FIG. 2.—Different types of atomic absorption systems.Detectors are usually photomultipliersand some instruments carry two to coverappropriate wavelengths. A wide-range one,\93 to 853 nm., d u e to its better red sensi tivity, is more ' noisy '.Flame emission spectroscopy is simple inprinciple and unknowns are merely checkedagainst calibrated standards. Snags includereproducibility problems—results vary from ay to day a n d consistency a n d concordancydepend very largely on experience, goodfortune, and a ' well-disciplined ' burner.T h e aluminium/phosphate with calciumproblem was overcome by using a dopedfadiation buffer *, e.g., l a n t h a n u m , barium,and yttrium do not allow calcium to complex.Additives removed the aluminium/phosphateFlameLensSlicFlameF i o . 3.—Ahernative optics for atomic a b s o φ t i o nsystems.measured. T h e profile of the energy theatom accepts is extremely small a n d noabsorption occurs until this small b a n d widthis reached. It is about 0 3 A across andgenerally m u c h less, say, o-i A. T h e secretof such a n energy source is the hollowcathode l a m p which is really a quiet dis charge tube {Fig. 5). A glow discharge is setSlit
MEDICINE, SCIENCE, AND THE LAWMedicine Sei. Law1973. Jan.Roonant mplitudtAElement line spectrum emitted by hollow cithode l» PΒSample absorbs cnerf χ at the resonanca lineCResultant spectrum after absorption100(l-X)ADMonochromator isolates resonance wavelenfthΕPhotodetector sees only resonance line diminishedby absorptionFio. 4.— The instrument principle involved in the atomic absorption process.
Volume 13Number 1HORNCASTLE : ATOMIC ABSORPTION SPECTROPHOTOMETRYUp—atoms leave a n d emit energy of exactlythe same frequency required for absorption.Lamps are available for each element a n dthey are sometimes equipped with a ' getter '(e.g., a magnesium foil strip) which mops u pany oxygen or even nitrogen formed. Adrawback is that they tend to soften a n d loseintensity. H i g h brightness a n d multipleelement lamps are also available {Fig. 5).I n the second case light is directed throughthe flame a n d the intensity with and withoutsample absorption is compared.Lightemission resulting from the flame can beeliminated by modulating the output of thehollow cathode l a m p if a light chopper isinserted between the source a n d the flame.Rejection of the d.c. signal contributed byflame emission is achieved by feeding theInert gasArgon or neonAnode /Anode« 0 V . d.c,3 - 6 mA.Silica window450 v. d.c.30 mA./Au; ciliary electrodesCathodeCathodeHollow cathode lampHigh brightness lampFIG. 5.—Alternative lamps for atomic absorption rptionΔ-0LampChopperFIO. 6 . — T o show the similarity between emission and absorption systems in atomic spectrophotometry.Alternatives are vapour discharge lamps(lithium, sodium, mercury, zinc, etc.) whichprovided they are under run, i.e., not a t fullpower, give a good signal; microwave-powereddischarge lamps composed of very high purity''materials; xenon arc continuous white lightsources, one only of which is required for any"tetal; a n d a plasma usually of radio-frequencytype into which ions are sprayed.T h e marked similarity between emissiona d absorption systems is evident from aeonsideration of Fi . 6.detector signal to a tuned a.c. amplifier butthis advantage is gained at the expense of aloss of overall energy to the detector.Both techniques d e m a n d similar sampling,flames, a n d measuring devices. For results,total intensity is important in the emissioncase; for absorption the optical density ismeasured (Elwell a n d Gidley, 1966).PARAMETERS AFFECTING THE SIGNALT h e combined laws of Beer a n d L a m b e r tapply.
10MEDICINE, SCIENCE, AND THE LAWI n the flame the particles are those inthe ground state.Absorbance A kxtigL,(i)where Αχ absorption coefficient, L lengthof the flame through which the light passes,and n„ atom concentration.T h e atom concentrationin the stream ing gases is proportional to the mass quantitytirria of atoms generated in the time intervalΔ/, i.e.,η. δ.-AM„AM/T h e feeding rate ofinto theflamedetermines the generation rate of the atomicspecies.It is only if the flame will convert totalmasses of introduced solute into the atomicground state t h a t : AmaAt Usually this is not so, a n d , in general.AmaAm/where— efficiency factor for atom genera tion in the flame. From equations ( i ) , (a),a n d ( 3 ) , therefore,A kx.d .-4T " . ¿ *A · δ . ÍAt(4)Similarly,AmiAms -oc-AtAtwhere the right-hand side denotes the spray ing rate.Again,AirifArru(For Beckmann-type burners,is unity, butfor atomizer chamber systems ? Β · · )T h e relationship (4) c a n now be written inthe form:Akx . h . tj . eg(5)where8-,-w.L.'¿ is a constant, vu the width of the flame, Lits length, a n d Vf the burning velocity.T h e interaction of the various factors ofequation (5) m a y be appreciated from Fig. 7.T h r e e basic designs of instrument exist {seeFig.2).Atomic absorption methods are very muchin favour for forensic work because in conventional laboratory flames the ratio ofunexcited to excited atoms at a given instantis large (Table II). T h e relationship(2)Atwhere δ a constant which depends onflame geometry, streaming, velocity of gases,etc.AmfAtMedicine Sei. U w1973. Jan.Vf'ocexp.(- ,/, ).Noapplies where Nj — the n u m b e r of atoms inthe excited state, N, the n u m b e r of atomsin the ground state, Ej the energy difference between the ground a n d excited states,k Boltzmann constant, a n d Τ absolutetemperature.Hence the higher Ej (i.e., the shorter thewavelength of the corresponding spectralline) the smaller will be the fraction of theatoms in the excited states. O n this accountzinc a n d magnesium, for example, are notsuitable for flame photometry but the alkalimetals are.Sensitivities are compared for flame emis sion a n d atomic absorption for the elementsof interest to the present study (Tables III a n dIV).Ways of improving the sensitivity of themethod include increasing the path lengtheither by projecting the flame through aheated silica tube or by a Beckmann-typemulti-reflectance technique. Scale expan sion, u p to one hundred times if needed, is analternative. A Boling burner—a three-slotvariety—with a very hot centre cuts downinterference effects a n d is especially good forcalcium, strontium, barium, molybdenum,chromium, and tin.Methyl a n d ethyl alcohols were used byBarry, Chappell, a n d Barnes (1946) toimprove emission in the case of sodium a n dpotassium. T h e employment of organicsolvents a n d chelating agents, such as M I B Kand a m m o n i u m pyroUidine dithiocarbamate(APDC), particularly in heavy metal analysisover a wide pH range followed for atomicabsorption. Organics of this type carry a n dvaporize more material in the flame. T h e
Volume 13Number 1HORNCASTLE: ATOMIC ABSORPTION SPECTROPHOTOMETRYparticular case of lead sensitivity with different solvents is shown in Table V (Read a n d n o t t , 1968). I n summary, it can be said thatFlame g e o m e t r yFlame t y p eW i d t h and lengthI Iemission a n d absorption a r e complementarya n d cater for almost the entire periodic table,Dual-purpose instruments a r e available.Delivery systemSprayerΐ{Direct spray o rSupport gasspray chamber ( h o t ) o r — p r e s s u r e sspray chamber (cold)Streaming velocityCoal ous oxideSolventAElement t o be determinedFlo. 7 , — T o show the interaction of parameters affecting the signal seen in the atomic absorption process.Direct effects,secondary effects.Table II.—ToELEMENTCaesiumSodiumCalciumZinc" able HI,—DETECTIONSHOW R A T I O OF U N E X C I T E D TO EXCITED ATOMS FOR COMMON ELEMENTSWAVELENGTHOF S P E C T R A LLINE8521589042272139AAAA, A T D I F F E R I.NT T E M P E R /ATURES2000 C.3000 c.3000 C.4-4 X 10-* 7-2 X I O - ' 3-0X IO *9-9 X 1 0 - · 5-9 X I 0 - * 4-4 X l o - ä1-2 X I O - ' 3-7X 1 0 - ' 6 - o x io *7-3 X I 0 " 5-6 X i o - ' » i-5X 1 0 - '5000 C.6·8χ ΙΟ-»1-5 X i o - «3-3 X4-3 X 1 0 - ·LIMITS BY FLAME EMISSION A N D ATOMIC ABSORPTION COMPARED FOR SELECTED ELEMENTS(UR. per 0210100,000
Medicine Sei. L«w1973, Jan.MEDICINE, SCIENCE, AND THE LAW12APPLICATIONS AND PROBLEMSAlthough apparently simple, accurate, a n dprecise for most elements, atomic absorptionspectrophotometry requires careful labora tory technique. I t is at least as good asalternative methods a n d superior to some.Valid comparisons must be based on totalelemental composition of a specific samplebecause some elements interfere in onemethod but not in another. I n any event itwould be foolish to relinquish sound a n dproven chemical methods (Reynolds, 1968).Gravimetric and volumetric proceduresapply to elements greater than 10 per cent inconcentration.Titre precision involvingvolumetric methods is less than 3 parts perthousand a n d weights involving gravimetricmethods are more accurate. Photometricmethods a r e most popular b u t few colourreactions are specific. Electrochemistry isleast used for routine analysis but coulombmetric methods surpass atomic absorptionin that that have been applied to 10-* M.Table IV.—COMPARISONM O R E SENSITIVEBY ATOMIC ABSORPTIONsolutions. Schematically a correlation m a ybe m a d e t h u s : —GravimetryTitrimetryPhotometryElectrochemical methodsAtomic absorptionΙΟ 10 PartsΙ O"Absolute detection limits are lower foratomic absorption than in photometry forabout two-thirds of the listed elements. Thisis very impressive when considering ' T h echemical analyses of things as they are '.A comparison of spectrographic a n dphotometric determinations of cobalt rockOF SENSITIVITIES*ABOUT curyMagnesium15 elementsΙ Ο niumM O R E SENSITIVEBY FLAME mLithiumSodium8 elementsI IRubidiumStrontiumThalliumelements* Sensitivities reported in the literature using a variety of instruments.Sensitivity is the concentration in aqueous solution which will produce an absorption of i per cent.Detection limit is the concentration in aqueous solution which gives a signal twice the size of the variability of thebackground.TableOP L E A D w r m D I F F E R E N TSOLVENTS (1 μ g . lead per ml. nWATERCCl/XYLENEMIBKf1-6305-06-6 C a r b o n tetrachloride with lead present as leaddithizonate.j M I B K — methylisobutyl ketone.specimens gave the following figures: 45 partsper million (the mean of 52 a n d 38) a n d 38parts per million (the average of 44, 32, a n d38) respectively. T h e relative precision ofchemical methods a n d atomic absorptionestimations of cobalt in two laboratories ledto the interesting results shown in Table VI(Lewis, 1968).Since dilute solutions are employed, lossesand errors by contamination from reagents
NumberHORNCASTLE: ATOMIC ABSORPTION SPECTROPHOTOMETRYand vessels must be considered. Adsorptionof metal ions from the walls of the vessel isinsidious and depends on pH, the concentra tion of the ionic species, a n d the history of thecontainer. T h e use of a ' master ' standard,changed every 14 days, is advocated. Poly ethylene bottles are best for storage and a pHof a or less is recommended. Contaminationproblems generally arise when working a tconcentrations below 0 0 1 p e r cent, i.e.,too parts per million, because large quantitiesof reagents a r e needed for dissolution.Furthermore, it must b e remembered t h a tpure ' acids contain traces of metals.Advantages of atomic absorption spectro photometry may be listed as specificity (apartfrom some isotopic overlap), low detectionhmits, several elements can be determined inone sample, and one can operate on smallersamples than in some chemical methods. I naddition, many elements can b e surveyed i t h t h e o n e instrument, a n d there isfreedom from time elapsing during colourTable VI.—ESTIMATION13copper o-i to 20 mg. per litre (o-i to 20parts per million) a n d zinc o-oa to 3 mg. perlitre (o-oa to 3 parts per million).A m o n g disadvantages of atomic absorp tion spectrophotometry a r e failures withsome lamps, too much trouble with t h enebulizer, a n d t h e scarcity of informationregarding the determination of major con stituents.Suitable precision, adequate sensitivity,acceptable drift, allowable blank, a n d asatisfactory calibration curve a r e necessaryfor best accuracy.T h e instrument performance must b echecked in respect of sensitivity, t h e driftmeasured, a n d limits established for it.Clogging of t h e burner affects t h e zero.Blanks should be determined on reagents a n don the substances, such as matrix metal andsalts used to suppress interferences, that areadded to calibration solutions. Standardaddition is preferred wherever possible.Recalibration should be performed a n dOF C O B A L T R O C K SPECIMENS BY CHEMICAL M E T H O D S A N D ATOMIC ABSORPTIONSPECTROPHOTOMETRYCHEMICALMETHODSCobalt determination (mean)Coefficient of variation(percentage)ATOMIC 30-71o-gidevelopment a n d drying of precipitates. AUthis is a t relatively low cost, althoughsophisticated apparatus a n d elaborate access ories can be expensive.More t h a n 50 p e r cent of instruments"Ought have been applied to biochemical andagricultural projects. Analyses of some 68elements are reported.Versatility is evident from assays between 'tic, copper, sodium, potassium, calcium,"Magnesium, iron, lead, chromium, m a n ganese, a n d c a d m i u m in waste water a n d calcium, magnesium, strontium, manganese,"'ckel, copper, and zinc in sea water. Typicalquantitative results for industrial water andindustrial waste water respectively a r e formultiple readings taken and bracketed withaverage values used.Sensitivity decreases as the concentrationincreases for those lines with large curvature,e.g., cobalt {Fig. 8).Ideally, t h e field should be adorned bycritical evaluation, adequate description,inter-laboratory testing, a n d agreement o nrecommended practices.SURVEY 1 (A3000)ProcedurePost-mortem urine samples were examinedfor t h e levels of t h e following elements{Table VII). A n A3000 atomic absorptionspectrophotometer was used.
Medicine Sei. Law1973, Jan.MEDICINE, SCIENCE, AND THE LAW14Sensitivity for boron is quoted as 50 partsper million for i per cent absorption using anitrous oxide/acetylene flame; this elementwas not attempted therefore on the instru ment available since it was adjudged froma heavy sediment. Aliquots were taken aftervigorous shaking b u t probably the speed atwhich the solids settled caused the samplingto be non-representative a n d some resultsmay have suffered accordingly.Table VII.—EXPECTEDCONCENTRATIONS OF ELEMENTSIN POST-MORTEM U R I N E SAMPLESE X P E C T E D CONCENTRATIONELEMENTParts tBoronManganeseZincC o n c c n t r i t i o n (mg. per here)F i o . 8.—To show the relationshipbetweenabsorbance a n d concentration.T h e sensitivitydecreases as concentration increases for those lineswith large curvature, e.g., cobalt.earlier colorimetric work that the levelswould be much lower than this limit.Samples as received at the laboratory h a dusually aged somewhat and many containedTable6000-90003750-52501 5 - 45015909-3N o n e quotedN o n e quotedN o n e quotedN o n e quotedG. perι·5 2NoneNoneNoneNonequotedquotedquotedquotedWith fresh samples, there were generallyno problems of this type, a n d they could besprayed directly into the instrument for thelower concentration elements.Suppression of calcium a n d magnesiumabsorbance by phosphate was expect
Number l HORNCASTLE : ATOMIC ABSORPTION SPECTROPHOTOMETRY Atomic Absorption Spectro photometry D. C. J. HORNCASTLE M.Sc, Ph.D., F.R.I.C, F.R.S.H. Summary HISTORICALLY flame emission spectroscopy Was developed first. Routine analysis showed the advantage of measuring absorption over emission for many metals. Instrumentation " equirements are:—
Chapter 8 Atomic Absorption Spectrophotometry Atomic Spectroscopy Methods that deal with absorption and emission of EMR by gaseous atoms The methods deal mainly with the free atoms (not ions) Line spectra are observed Specific spectral lines can be used for both qualitative and quantitative analysis of elements
Atomic absorption spectrophotometry is considered the method of choice for hepatic iron quantification. The ob-jective of the present study was to perform full validation assays of hepatic iron quantification by atomic absorption spec-trophotometry, using a fast sample preparation procedure, following the guidelines from the International .
applications using molecular absorption, fluorimetry and resonance light scattering spectrophotometry are presented. Based on the literature data and the experience in the field, challenges and perspectives in the ion-pair spectrophotometry are also considered. KEYWORDS: Ion-pair spectrophotometry, pharmaceuticals, UV-VIS absorption,
forplasmaquantitated byatomic absorption spectrophotometry. 'THE TECHNIC ofatomic absorption spectroscopy has recently been adopted with increasing confidence inclinical biochemistry. Emphasis has largely been onthemeasurement ofcalcium and magnesium (1-16), although the trace metals zinc (17, 18), copper (19, 20), and lead (18,
metals by atomic absorption spectrophotometry in commercially available multivitamins. Journal of Contemporary Research in Chemistry, 1(1), 51-59. INTRODUCTION It is need of the day to develop analytical methods for precise determination of hazardous material in foodstuff and pharmaceutical products, particularly in nutritional supplement drugs .
44 Flame Emission - it measures the radiation emitted by the excited atoms that is related to concentration. Atomic Absorption - it measures the radiation absorbed by the unexcited atoms that are determined. Atomic absorption depends only upon the number of unexcited atoms, the absorption intensity is not directly affected by the
absorption spectrophotometry (FAAS)3 or Electrothermal atomization Atomic absorption spectrophotometry (ETAAS)4-6, high performance liquid chromatography7-10, chelation ion chromatography11-12, electroanalytical techniques13-15,Neutron activation analysis (NAA)6, X-ray fluorescence (XRF)17-18, and spectrophotometric methods19-22.UV- .
R&D projects, but there are doubts on how many innovations have effectively gone to the market. The mid-term evaluations show outputs and results coming out of collective actions and support to regional filières and clusters. 2011 is the first year with outputs in the field of
