Ultra-trace mercury determination in seawater after vortex-assisted liquid-liquid micro-extraction

In the present study, an analytical methodology based on a vortex-assisted liquid-liquid micro-extraction (VALLME) was developed for extraction and enrichment technique of total mercury (Hg) from seawater after derivatisation with ammonium pyrrolidine dithiocarbamate (APDC), while Hg quantitation was performed by atomic absorption spectrometry (AAS) using a Direct Mercury Analyser DMA-80 spectrometer based on thermal desorption. Variables affecting Hg derivatisation (including pH and APDC concentration) and VALLME extraction (comprising extraction (vortex) time, acceptor solvent (hexane) volume and ionic strength of donor phase) were explored. Enrichment factor (EF) and extraction recovery (ER) of 51 and 76 & PLUSMN; 5.3% were obtained from only 20 mL of seawater (at pH = 3) when using an APDC concentration of 0.125 mmol/L, and vortex time and acceptor solution volume of 4 min and 300 & mu;L, respectively; whereas NaCl addition had no effect on Hg determination. The VALLME-AAS method has been high sensitive (quantification limit, QL = 10.3 ng L-1) and precise (with relative standard deviations, RSDs of <14%). The developed procedure has been tested by analysing different sea water (NASS-7) and estuarine water (SLEW-3 and BCR-505) certified reference materials. Finally, Hg levels between 34 and 172 ng L-1 have been assessed in several seawater samples at A Corun & SIM;a bay.

Automated summary

In this study, a vortex-assisted liquid-liquid micro-extraction (VALLME) method was developed for extraction and enrichment of total mercury (Hg) from seawater. The method involved derivatisation of Hg with ammonium pyrrolidine dithiocarbamate (APDC) and quantitation by atomic absorption spectrometry (AAS). Variables affecting the derivatisation and VALLME extraction were investigated. The developed method showed high sensitivity and precision, with an enrichment factor of 51 and extraction recovery of 76% when using specific conditions. The method was validated using certified reference materials and applied to assess Hg levels in seawater samples.