Pergamon zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Specmchimica Acm, Vol. 498, No. 7, pp. 655-675, 1994 Copyright 0 1994 Ekvier Science Ltd Printed in Great Britain. AU rights reserved 0584-8%7/94 s7.cm + .oo 0584-8547(94@002bo Interference mechanisms of sodium chloride on graphite furnace atomic absorption spectrometry platform S. AKMAN and G. DINER zinc and cobalt in using a dual cavity zyxwvutsrqpon Ista nb ul Teknik ijniversitesi, Fen-Edebiyat Fakiiltesi, Kimya Boltimti 80626 Maslak/Istanbul, Turkey zyxwvutsrqpon (Received 26 October 1993; accepted 7 March 1994) Abstract-The interferences of sodium chloride with the determination of a volatile (zinc) and a low volatility (cobalt) element by graphite furnace atomic absorption spectrometry (GFAAS) were examined. For various masses of the sodium chloride, the effects of pretreatment temperature and time, and heating rate on the atomization of the analyte were investigated using a specially designed dual cavity platform, which in principle allows the analyte and the interferent to vaporize from the separate cavities so that gas and condensed phase interferences can be distinguished to some extent. In addition, background and atomic absorption signals obtained in the pretreatment step provided very important information to clarify the interference mechanisms. In the presence of sodium chloride, formation of a highly volatile zinc chloride contributes mainly to the losses of zinc, especially during high pretreatment temperatures. The losses of zinc and cobalt can partly be attributed to the occlusion of the analytes in microcrystals of the interferent and some of these are thrown from the furnace without decomposing early in the atomization step or during the pretreatment step. In addition, expulsion of both analytes together with the violently expanding matrix gases seems to be a likely interference mechanism as well. 1. INTR~DUC~~N THE EFFECT of numerous matrices on the sensitivity of various elements in graphite furnace atomic absorption spectrometry (GFAAS) has been widely investigated. The use of stabilized temperature platform furnace (STPF) conditions [l] together with proper modifiers has been very helpful in eliminating most of the interferences. However, in some cases, determinations in GFAAS, even with STPF conditions, are not free from interferences [2]. It is very important and necessary to know the mechanisms of interferences for their better control and elimination by selecting proper experimental conditions and modifiers. Chloride matrices, especially sodium chloride, have been the most widely studied interferents owing to their presence as the major component in various samples as well as their severe interferences on the determination of many elements in GFAAS. In order to explain the interferences from chloride-containing matrices, a gas-phase reaction between analyte atoms and chlorine has been proposed by many workers [3-71. However, with the use of STPF conditions, most of these gas-phase reaction interferences have been greatly or completely eliminated [l]. Expulsion of the analyte together with rapidly expanding matrix gases was proposed by HOLCOMBE [8] and WELZ et al. [g-11]. This mechanism is especially predominant when the interferent is excessively decomposed owing to the fast heating rate applied in the atomization step. Co-volatilization [12] or carrier effects [13] can also be considered as an expulsion mechanism. Occlusion of the analyte in a rather refractory matrix of microcrystals, which are thrown from the atomizer in the atomization step without decomposing, has been suggested by some authors as a primary interference of some alkali and alkaline earth chlorides on Cd, Cr, Cu, Pb and Mn [14-171. MATOUSEK [18] argued that occlusion caused interference only if the matrix could not be dissociated during the atomization step and if the matrix could be fully volatilized during the atomization step, the occlusion effect would be reflected only