Trace-level automated mercury speciation analysis

Abstract

An automated system for methyl Hg analysis by purge and trap gas chromatography (GC) was evaluated, with comparison of several different instrument configurations including chromatography columns (packed column or capillary), detector (atomic fluorescence, AFS, or inductively coupled plasma mass spectrometry, ICP-MS, using quadrupole and sector field ICP-MS instruments). Method detection limits (MDL) of 0.042 pg and 0.030 pg for CH₃Hg⁺ were achieved with the automated Hg analysis system configured with AFS and ICP-MS detection, respectively. Capillary GC with temperature programming was effective in improving resolution and decreasing retention times of heavier Hg species (in this case C₃H₇Hg⁺) although carryover between samples was increased. With capillary GC, the MDL for CH₃Hg⁺ was 0.25 pg for AFS detection and 0.060 pg for ICP-MS detection. The automated system was demonstrated to have high throughput (72 samples analyzed in 8 h) requiring considerably less analyst time than the manual method for CH₃Hg⁺ analysis described in EPA 1630.