Ultra-trace mercury determination in drinking water by APGD-OES with cold vapor generation and gold trap enrichment

An atmospheric pressure glow discharge (APGD) optical emission spectrometry (OES) method for ultra-trace Hg determination in water was developed by combining cold vapor (CV) generation with a custom-built gold trap (GT). Among the two high-voltage power supplies evaluated (pulsed DC and constant DC), the constant DC-driven microplasma yielded superior Hg excitation. Under optimized conditions, limits of detection (LODs) for Hg in CV-APGD-OES were 0.2 and 0.08 μg L^-1 for 1 s and 10 s integration times, respectively. Coupling with the GT unit improved sensitivity by over 100-fold, yielding an LOD of 0.003 μg L^-1, well below regulatory limits for drinking water. Time-resolved signal measurements (intensity of the Hg I 253.7 nm line) were fitted to an exponentially modified Gaussian function (EMG), enabling repeatabilities of 4.2% and 2.2% at concentration levels of 0.25 and 5 μg L^-1, respectively. The method was validated using spiked water samples (sub-μg L^-1 levels), with recoveries of 98-108%. Compared to conventional, bulky systems, the proposed approach offers reduced costs, simplified instrumentation, and lower maintenance requirements.