FIELD AND LABORATORY PROCEDURES FOR DETERMINING GOLD IN NATURAL-WATERS - RELATIVE MERITS OF PRECONCENTRATION WITH ACTIVATED-CHARCOAL

The critical parameters and merits of a method to determine Au in waters by initial adsorption on to activated charcoal, and measurement by graphite furnace atomic absorption spectrometry (GFAAS) have been examined. Results of this study show that pH adjustment and intense mixing of the activated charcoal in the sample are prerequisites to complete adsorption of the Au. Thus, provided that such preparation facilities exist in the field area, this method would enable low-cost shipment of filtered activated charcoal discs to the laboratory where they would be analyzed relatively inexpensively and rapidly by GFAAS. A determination limit of 0. 5 ng L** minus **1 (parts per trillion), based on adsorption from a 1-L sample, is achieved with a relative standard deviation of about plus or minus 10% at the 5 ng L** minus **1 level. However, if acidification and filtration are not possible in the field or within a one-day delay period, then an alternate method is proposed, which is more time-consuming in the laboratory and entails costly shipment of bulky samples but may be the only feasible choice for some field situations.