Ultratrace mercury speciation analysis in rice by in-line solid phase extraction – liquid chromatography – atomic fluorescence spectrometry

For the first time, Hg2+ and methylmercury speciation analysis was accomplished by in-line SPE-LC-AFS. After modification with 0.1 mL of 0.001% (m:v) sodium diethyldithiocarbamate, a C18 microcolumn retained Hg2+ and MetHg in rice extract within 3 min; the captured Hg species were separated within 12 min in 0.25% (v:v) 2-mercaptoethanol + 60 mmol L-1 (m:v) ammonium acetate + 4% (v:v) acetonitrile. Under optimized conditions, the detection limits were 0.3 ng L-1 for Hg2+ and 0.2 ng L-1 for MetHg, respectively, with 10 mL injection vs. 0.1 mL eluent; in-line SPE achieved ∼ 100x enrichment. Method precision and accuracy were satisfactory at < 2% relative standard deviations (RSDs) for 20 ng L-1 of Hg2+ and MetHg and 95-102% recoveries for real rice samples. In-line SPE obviated human involvement and avoided invalid transportation between interfaces, rendering this SPE-LC-AFS method easy, compact, robust, yet sensitive in mercury speciation analysis to uphold food safety.