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9 3 2 9 3 3 9 3 4 9 3 5 9 3 6 9 3 7 9 3 8 beam IfnocorrectIOnISmade,sampleabsorbancewIllbegreaterthanItshouldbe, and the analytIcal result wIll be erroneously hIgh If dunng atomIzatIOn all the analyte IS not volatIlIzed and removed from the furnace, memory effects wIll occur ThIS condItIOn IS dependent on several factors such as the volatIlIty of the element and ItS chemIcal form, whether pyrolytIc graphIte IS used, the rate of atomIzatIon and furnace desIgn If thIS sItuatIOn IS detected through blank burns, the tube should be cleaned by operatIng the furnace at full power for the reqUIred tIme penod as needed at regular Intervals In the analytIcal scheme Some of the smaller SIze furnace devIces, or newer furnaces eqUIpped wIth feedback temperature control (InstrumentatIOn Laboratones MODEL 555, PerkIn-Elmer MODELS HGA 2200 and HGA 76B, and VarIan MODEL CRA-90) emploYIng faster rates of atOmIZatIOn, can be operated USIng lower atomIzatIon temperatures for shorter tIme penods than those lIsted In thIS manual Although pnor dIgestion of the sample In many cases IS not reqUIred provIdIng a representative alIquot ofsample can be pipeted Into the furnace, It wIll provIde for a more unIform matnx and possIbly lessen matnx effects Inject a measured mICrolIter alIquot of sample Into the furnace and atomIze If the concentratIOn found IS greater than the hIghest standard, the sample should be dIluted In the same aCId matnx and reanalyzed The use of multiple Injections can Improve accuracy and help detect furnace pipettIng errors To venfy the absence ofInterference, follow the procedure as gIven In part 5 2 I A check standard should be run approxImately after every 10 sample InjectIOns Standards are run In part to mOnItor the lIfe and performance of the graphIte tube Lack of reproducIbIlIty or sIgnIficant change In the sIgnal for the standard IndIcates that the tube should be replaced Even though tube lIfe depends on sample matnx and atomIzatIOn temperature, a conservatIve estImate would be that a tube wIll last at least 50 fmngs A pyrolytIc-coatIng would extend that estimate by a factor of3 CalculatIOn-For determInatIOn of metal concentratIOn by the furnace Read the metal value In ug/l from the calIbratIOn curve or dIrectly from the readout system ofthe Instrument 9 3 8 I If dIfferent SIze furnace InjectIOn volumes are used for samples than for standards ug/lofmetalIn sample =Z ( ~) where Z = S = U = ug/l ofmetal read from calIbratIOn curve or readout system ul volume standard Injected Into furnace for calIbratIon curve ul volume ofsample Injected for analYSiS MET ALS-I7PDF Image | Methods for Chemical Analysis of Water and Wastes
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