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6 Apparatus 6 1 62 63 6 4 Atom1c absorptlOn spectrophotometer Smgle or dual channel, smgle-or double-beam mstrument havmg a gratmg monochromator, photomultipher detector, adjustable shts, a wavelength range of 190 to 800 nm, and prov1s1ons for mterfacmg w1th a stnp chart recorder Burner The burner recommended by the partlCular mstrument manufacturer should be used ForcertamelementsthemtrousoX1deburner1SreqUlred Hollow cathode lamps Smgle element lamps are to be preferred but mult1-element lamps maybeused Electrodelessd1schargelampsmayalsobeusedwhenaval1able Graph1te furnace Any furnace deV1ce capable of reachmg the spec1fied temperatures 1S sat1sfactory 5 2 4 5 2 5 5 2 6 5 2 7 5 2 8 5 2 9 the presence of a1r Care must be taken, however, to prevent loss of the analys1s element Samples contammg large amounts of orgamc matenals should be oX1d1zed by conventional aC1d d1gestlOn pnor to bemg placed m the furnace In th1S way broad band absorptlOn wl1l be m1mm1zed From amon mterference stud1es m the graph1te furnace 1t 1S generally accepted that mtrate1Sthepreferredamon ThereforemtncaC1d1Spreferableforanyd1gestlOnor solub1hzatlOn step If another aC1d m add1tion to HN03 1S reqUlred a m1mmum I amount should be used Th1S apphes part1cularly to hydrochlonc and to a lesser extent to sulfunc and phosphonc aC1ds Carb1de formatlOn resultmg from the chem1cal enVironment of the furnace has been observed w1th certam elements that form carb1des at h1gh temperatures Molybdenum may be c1ted as an example When th1S takes place, the met~lwl1l be released very slowly from the carb1de as atom1zatlOn contmues For molybdenum, one may be reqUlred to atom1ze for 30 seconds or more before the slgnal returns to basehne levels Th1s problem 1S greatly reduced and the sens1t1v1ty mcreased w1th the use ofpyrolytically-coated graph1te Iomzation mterferences have to date not been reported w1th furnace techmques For comments on spectral mterference see sectlOn 5 1 5 ContammatlOn of the sample can be a major source of error because of the extreme sens1t1v1ties ach1eved w1th the furnace The sample preparatlOn work area should be kept scrupulously clean All glassware should be cleaned as d1rected m part 6 9 of the Atom1C AbsorptlOn Methods sectlOn of th1S manual P1pet tips have been known to be a source of contammatlOn If suspected, they should be aC1d soaked w1th 1 5 HN03 and nnsed thoroughly w1th tap and delOmzed water The use of a better grade p1pet tip can greatly reduce th1S problem It 1S very 1mportant that special attentlOn be glven to reagent blanks m both analys1s and the correctlOn of analytlCal results Lastly, pyrolyt1c graph1te because of the productlOn process and handlmg can become contammated As many as five to poss1bly ten h1gh temperature burns may be reqUlred to clean the tube before use MET ALS-9PDF Image | Methods for Chemical Analysis of Water and Wastes
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