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volume has been reduced to 15-20 ml makIng certam the samples do not boll (If the sample IS bemg prepared for furnace analYSIS, the same process should be followed except HCl should be omItted) After thIS treatment the sample IS filtered to remove sIhcates and other msoluble matenal that could clog the atomIzer and the volume adjusted to 100 ml The sample IS then ready for analYSIS ConcentratIOns so determmed shall be reported as "total" (See Notes 4, 5, and 6 ) NOTE 5: The analyst should be cautIOned that thIS dIgestIOn procedure may not be suffiCIently VIgorous to destroy certam metal complexes Ifa colonmetnc procedure IS to be employed for the final determmatIOn When thIS IS suspect, the more VIgorous dIgestIOn gIven m 4 1 3 should be followed NOTE 6: For dnnkmg water analyses by dIrect aspIratIOn, the final volume may be reduced to effect up to a lOX concentratIon of the sample, provIded the total dIssolved sohds m the ongmal sample do not exceed 500 mg/l, the determmatIOn IS corrected for any non-specIfic absorbance and there IS no loss by preCIpItatIOn 5 Interferences 5 1 DIrect AspIratIOn 5 1 1 The most troublesome type of mterference m atomIC absorptIOn 5 1 2 5 1 3 spectrophotometry 18 usually termed "chemIcal" and IS caused by lack of absorptIOn of atoms bound m molecular combmatIOn m the flame ThIS phenomenon can occur when the flame IS not suffiCIently hot to dISSOCiate the molecule, as m the case of phosphate mterference WIth magnesmm, or because the dISSOCIated atom IS ImmedIately OXIdIzed to a compound that WIll not dISSOCIate further at the temperature of the flame The addItIOn of lanthanum WIll overcome the phosphate Interference In the magnesmm, calcmm and banum determInatIons SImIlarly, sIhca mterference m the determmatIon of manganese can be ehmmated by the addItIon of calcmm ChemIcal mterferences may also be ehmmated by separatmg the metal from the mterfenng matenal WhIle complexmg agents are pnmanly employed to mcrease the senSItIVIty of the analYSIS, they may also be used to ehmmate or reduce mterferences The presence of hIgh dIssolved sohds m the sample may result m an mterference from non-atomIC absorbance such as hght scattenng I f background correctIOn IS not avaIlable, a non-absorbmg wavelength should be checked Preferably, hIgh sohds type samples should be extracted (see 5 1 1 and 9 2) 5 14 IOnIZatIOn Interferences occur where the flame temperature IS suffiCIently hIgh to generate the removal of an electron from a neutral atom, gIvmg a pOSItIve charged Ion ThIS type of Interference can generally be controlled by the addItion, to both standard and sample SolutIons, ofa large excess ofan easIly IOnIzed element 5 1 5 Although qUIte rare, spectral mterference can occur when an absorbmg wavelength of an element present In the sample but not bemg determmed falls withm the WIdth ofthe absorptIon hne ofthe element ofmterest The results ofthe determmatIon WIll then be erroneously hIgh, due to the contnbutIOn of the mterfenng element to the atomIC absorptIOn SIgnal Also, mterference can occur METALS-7PDF Image | Methods for Chemical Analysis of Water and Wastes
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