MICRODETERMINATION OF GOLD USING N-CYANOACYLACETALDEHYDE HYDRAZONE

A reliable and rapid procedure for the flotation and micro-determinati on of Au(III) using N-cyanoacylacetaldehyde hydrazone (CyAH) is propos ed. CyAH forms a blue 1:1 complex (K(f) = 4.1 x 10(5) mol-1 l-1) with Au(III) at pH 3-7. The maximum absorbance is obtained after 7 min; ins tantaneously by adding 3.3 x 10(-3) mol/l H3PO4 or by heating to 55-de grees-C. Beer's law is obeyed for 1 - 30 ppm of Au(III) with a molar a bsorptivity of 0.3 x 10(4) l mol-1 cm-1 at 550 nm. The reported method s [1 - 6] gave no evidence of the use of N-cyanoacylacetaldehyde hydra zone (CyAH) [7] for the determination or flotation of gold. It was fou nd that the suitable pH-range for complete developing (after 7 min) of the blue colour was 3 - 7. This pH-range could be achieved by adding the reactants (1:1) in aqueous solution (i. e. there was no need for a djusting the pH, unless otherwise specified). It has been found that t he absorbance of the Au(III)-CyAH system increases as the reagent conc entration increases due to the shift of the equilibrium in favour of t he complex. Maximum absorbance was obtained if equimolar amounts of bo th Au(III) and CyAH are added. A 10-fold molar excess of CyAH over Au( III) was used to ensured complete reaction. The following ions in amou nts 200-times that of the analyte ion do not interfere: nitrate, sulph ate, perchlorate, citrate, tartrate, oxalate, chloride, alkali and alk aline earth metals; the cations Bi3+ (0.4 mg), Cu2+ (1 mg), Al3+ (0.3 mg), La3+ (1.5 mg), Hg2+ (0.5 mg), Mn2+ (0.8 mg), Fe3+ (1 mg), Se4+ (0 .5 mg), Co2+ (1 mg), Ni2+ (1 mg) and Mo6+ (0.4 mg) are also tolerated. Pt4+ and Pd2+ interfere even at low level and must be eliminated by a dding trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (DCTA). The role of CyAH in preconcentrating traces of Au(III) using the flota tion technique was examined. The effects of oleic acid surfactant (HOL ) and CyAH concentrations, temperature, foreign ions, ionic strength a nd pH on the flotation efficiency of the Au(III)-CyAH system have been studied. Maximum flotability (100%) of Au(III) was achieved in the 4- 6.5 pH range. Most of the investigated foreign ions have no significan t effect on the flotation efficiency of the complex. Rising the temper ature to 55-degrees-C enhances the flotation. The following procedure was applied: Into a flotation cell [8], 7.5 mug of gold(III) was added to 20 ml of natural water (from different locations). To the cell, 1 ml of 10(-3) mol/l CyAH was added, the pH was adjusted to 6 using a fe w drops of HNO3 (1 mol/l) and the volume was made up to 25 ml with wat er. After 7 min, 2 ml of 25.44 x 10(-4) mol/I HOL was added to the cel l, which was turned upside down 20 times by hand for complete flotatio n of the Au-CyAH system. The mother liquor was separated from the cell . 1 ml of 1 mol/l HNO3 was added to the scum inside the cell, and the mixture was shaken thoroughly to elute the gold content from the scum. The eluted solution, together with the washing, was made up to a know n volume and divided into two parts. To the first part, 3 ml of 10(-3) mol/l CyAH, a few drops of 1 mol/l NaOH (for controlling the pH at ap proximately 6) were added and the volume diluted to 20 ml. The absorba nce was measured spectrophotometrically at 550 nm after 7 min at 25-de grees-C against CyAH as a blank. The second part was used for the AAS determination of gold for comparison as shown in Table 1. The precisio n of the method was determined by taking 10 measurements each with 0.5 ppm of the metal. The relative standard deviation was found to be 1.4 2%.