Preconcentration of submicrogram amounts of metals from natural waters for x-ray energy spectrometric determination using pyrrolidinecarbodithioic acid

Abstract

A method was developed for the routine determination of several trace metals in natural waters by X-ray ehergy spectrometry following precipitation wlth pyrrolidlnecarbodlthloate. Preoxldatlon wHh persulfate ellminates interferences by organlc m a t h . By optlmlzing carrier ion sete.ctlon and measurement conditions, one may determine dlthloate-reactlve elements wlth 2 I 50 by means of thelr K X-rays, and m e wkh 2 2 80 by means of thelr L X-rays. Determinations are feaslble for several elements at concentrations down to 250 ng L-', or below. Recoveries are generally greater than 90 %, although some exceptions are noted. Reproduclbllity wlth real samples averaged about 25% relative standard deviation for five representatlve element& at concentrations above 250 ng L-'.The merits 6f joining chemical precohcentration of trace ions to analysis by X-ray fluorescence spectrometry have been recognized for some time (1). Depending-on the circumstances, various ion-exchange; chelation-adsorption, and (co)precipitation techniques may be applicable. Two recent articles (2, 3) and a monograph (4) provide critical comparisons of the more promising procedures. Beginning several years ago, we focused our efforts on reducing to practice the use of the ammonium salt of pyrrolidinecarbodithioic acid (usually abbreviated APDC) as a precipitant for a variety of trace metals in natural waters (7-10).The procedure we developed is an elaboration of suggestions made earlier by Glcu and Schwab (5) and by Elder et al. (6). Metals are recipitated from pretreated water samples using precipitate is collected on a membrane filter and ahalyzed by X-ray energy spectrometry with secondary source excitation. Our findings are in general accord with those of Pik et al. (8), whose report appeared during the course of this work, except that we find that it is necessary to pretreat the sample to eliminate interference by organic matter. Leyden et al. (9) also report that humic and fulvic substances interfere with the reaction between metal cations and dithiocarbamate reagents.The improvements in technique we report here are (a) development of a compatible nonphotochemical procedure for oxidative destruction of interfering organic matter, (b) ex-APDC in t R e presence of an excess of a carrier ioh. The Present address: tension of the practical working range to well below 1 bg/L, and (c) optimization of carrier ion selection and measurement conditions to allow determination of APDC-reactive elements through 2 5 50 by means of their K X-rays, and some with 2 1 80 by means of their L X-rays.Preliminary experiments with filtered (0.45 gm) lake and rivgr water samples confirmetl that, even without any pretreatment other than pH adjustment, APDC is indeed capable of precipitating a variety of trace metal ions from real samples. Tests by the method of standard additions gave linear response plots. However, the slopes of these plots tended to vary from one sample to another, y d for several elements they were lower than the response slopes observed for stand...

Seasonal variations of heavy metal contamination in river Gomti of Lucknow city region

“…The organic layer was aspirated into the Atomic Absorption Spectrophotometer, Perkin-Elmer 5000 model without further concentration by following standard procedure (Horvard 2004;Tisue et al 1985).…”