Permanganate assisted oxidative-chlorination digestion for trace determination of gold in geological samples by GF...

Determination of gold in geological materials remains analytically challenging owing to its ultra-trace concentrations, heterogeneous distribution, and association with complex mineral phases. Aqua regia digestion is widely applied for gold analysis; however, alternative digestion strategies that provide enhanced control over oxidation and chlorination processes are of continued interest. Developing reagent-based systems capable of promoting efficient gold solubilization while maintaining compatibility with routine analytical instrumentation is therefore important for improving analytical reliability across a wide range of geological matrices.

A digestion method for the determination of gold (Au) in geological samples is presented as an alternative to conventional aqua regia digestion. The proposed method employs a controlled oxidative-chlorination system using potassium permanganate, sulphuric acid and sodium chloride to achieve quantitative solubilization of gold, followed by solvent extraction into methyl isobutyl ketone (MIBK) and determination by graphite furnace atomic absorption spectrometry (GF AAS). Method validation was performed using five certified reference materials (G320-9, GLG920-4, OREAS 45h, GLG904-2, and GPP-12), which yielded mean recoveries in the range of 93-102 % with low relative standard deviations (RSD), demonstrating good accuracy and precision across a wide concentration range. Comparative studies using traditional aqua regia digestion showed comparatively lower recoveries, particularly for reference materials having low Au concentration.

The proposed procedure reduces the consumptions of concentrated mineral acids, eliminates direct handling of aqua regia and generates reactive chlorinating species in situ, thereby decreasing chemical hazards and waste generation. The method provides a reliable, economically viable and safer alternative for routine determination of Au at trace level in geological matrices while maintaining analytical performance.