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The method of standard addItIons can be very useful, however, for the results to be va11d the followmg 11mItatIOns must be taken mto consIderatIOn a) the absorbance plot of sample and standards must be 11near over the concentratIOn range of concern For best results the slope of the plot should be nearly the same as the slope of the aqueous standard curve I f the slope IS sIgmficantly dIfferent (more than 20%) caution should be exercIsed b) the effect of the mterference should not vary as the ratIO of analyte concentratIOn to sample matnx changes and the standard addItIOn should respond m a sImIlar manner as the analyte c) the determmatIOn must be free ofspectral mterference and corrected for non- specIfic background mterference 9 General Procedure for AnalysIs by AtomIc AbsorptIOn 91 DIrect AspIratIon DIfferences between the vanous makes and models of satIsfactory atomIC absorptIon spectrophotometers prevent the formulatIOn of detaIled mstructIOns apphcable to every mstrument The analyst should follow the manufacturer's operatmg mstructIOns for hIS partIcular mstrument In general, after choosmg the proper hollow cathode lamp for the analysIs, the lamp should be allowed to warm up for a mmimum of 15 mmutes unless operated m a double beam mode Dunng thIS penod, ahgn the mstrument, posItIOn the monochromator at the correct wavelength, select the proper monochromator s11t WIdth, and adjust the hollow cathode current accordmg to the manufactuerer's recommendation Subsequently, 11ght the flame and regulate the flow of fuel and oXIdant, adjust the burner and nebuhzer flow rate for maXImum percent absorptIon and stabIhty, and balance the photometer Run a senes of standards of the element under analysIs and construct a cahbratIOn curve by plottmg the concentratIOns of the standards agamst the absorbance For those mstruments whIch read dIrectly m concentratIOn set the curve corrector to read out the proper concentratIOn AspIrate the samples and determme the concentratIOns eIther dIrectly or from the calIbratIon curve Standards must be run each time a sample or senes ofsamples are run 9 1 1 CalculatIOn - DIrect determmation of 11qUId samples Read the metal value m mg/l from the cahbratIOn curve or dIrectly from the readout system of the mstrument 9 1 1 1 IfdIlutIOn ofsample was reqUired mg/lmetalmsample=A (c~B) where A = B = C = mg/l ofmetal mdIluted ahquot from calIbration curve m1 of deIOlllzed dIstIlled water used for dIlutIOn ml ofsample ahquot MET ALS-13PDF Image | Methods for Chemical Analysis of Water and Wastes
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