Abstract
Inductively coupled plasma mass spectrometry (ICP-MS) was employed for the determination of gold in plant materials. Optimum conditions for maximum gold (197Au) signal were found to be a nebuliser flow rate of 1.02 l min-1 at a forward power of 1.2 kW. Dissolution of plant materials was achieved by investigating two procedures. Excellent recovery (102±3.6%) and reproducibility were obtained for procedure 2 (i.e. a simple aqua regia-hydrofluoric acid attack). Wash out with an 8% aqua regia solution eliminated gold ‘memory effects’. Internal standardisation was achieved by iridium (193Ir). Quality control assurance for gold analyses was insured by NIST 1571 Orchard Leaves and two ‘in-house’ reference materials. The methodologies developed were applied to three separate studies. Under experimental conditions bryophytes were treated with solutions containing gold and multi-elements. All species exhibited a high degree of gold accumulation, as high as 6.90 μg g-1 (dry wt.)-producing a percentage uptake from solution of 69%. Significant relationships were noted between gold levels and elements reported in the literature to be associated with gold (i.e. Ag, As, Fe). Secondly, a region of known gold mineralisation in Scotland was investigated. Three distinct zones of gold mineralisation were noted, with gold levels of 620 and 302 ng g-1 (dry wt.), in contrast to background levels of 3.9 and 4.2 ng g-1 (dry wt.) in plant and soil materials, respectively. Finally, plant and soil materials were removed from the vicinity of a gold mine in New Zealand. The highest gold levels were observed for bryophytes with a mean gold concentration of 4791 ng g-1 (dry wt.). This work highlights the analytical difficulties in determining gold in plant materials by ICP-MS and demonstrates the efficacious use of bryophytes as a plant medium for the uptake of gold.