Lin, Jhih-Min

The first part of research focused on ion-pair reversed-phase chromatography with inductively coupled plasma mass spectrometry for determination of mercury species in sludge samples. The separation of Hg(II), methyl-Hg and ethyl-Hg was performed on a reversed-phase C8 column with 2-mercaptoethanol and MeOH as mobile phase, since mercury had a strong affinity to thiol group of 2-mercaptoethanol. Under the optimized conditions, the separation of three mercury species was completed within 6.5 minutes by using isocratic elution program. The relative standard deviation of the peak heights and areas were less than 1.9% for the study species, and the detection limits of Hg(II), methyl-Hg and ethyl-Hg were found to be 0.013, 0.010 and 0.015 ng mL-1, respectively. In the extraction process, the mercury compounds were efficiently extracted from sludge samples by microwave-assisted extraction method, which using the mobile phase (0.3% (v/v) 2-mercaptoethanol and 3.5% (v/v) MeOH) containing 1.0% (v/v) HCl as the extracted reagent. We obtained an extraction efficiency of greater than 93% under heating at 60\ue2 for 8 minutes, and the spike recoveries of each individual mercury species were in the range of 95-102% to demonstrate the feasibility of the proposed method for sludge analysis. The research was applied to investigate mercury species in four environmental sludge samples, and results revealed that accumulation in sludge was predominantly Hg(II). While methyl-Hg would present in the high pollution water area, it might result from the microorganisms in downstream sludge which could transform Hg(II) into methyl-Hg.
The second part of research focused on ion-exchange chromatography with inductively coupled plasma mass spectrometry for determination of chromium and arsenic species in sludge samples. The simultaneous separation of Cr(III), Cr(VI), As(III), As(V), AsB, DMA and MMA was performed on an anion-exchange column by using gradient elution program with NH4NO3 as mobile phase, and the separation was using gradient elution program with NH4NO3 as mobile phase, and the separation was completed within 10 minutes. Since the detection of chromium and arsenic may suffer from the spectral interferences 40Ar12C+ and 40Ar35Cl+, a dynamic reaction cell (DRC) with O2 as reaction gas was employed to change the mass-to-charge ratio of analytes orinterfering substances to reduce these interferences, which could decrease the background signal and improve the detection limits. Under the optimized conditions of separation and DRC system, the relative standard deviation of the peak heights and areas were less than 2.7% for the study species, and the detection limits of species were in the range of 0.059-0.072 ng mL-1 for chromium and 0.009-0.015 ng mL-1 for arsenic. In the extraction process, chromium and arsenic species were extracted from sludge samples by microwave-assisted extraction method, which using the mobile phase B (40 mM NH4NO3) containing 1.0% (v/v) HF as the extracted reagent to destroy the sludge matrix. The extraction efficiency of chromium and arsenic were achieved 85% and 100% under heating at 90\ue2 for 40 minutes. The spike recoveries of each individual species were in the range of 92-106% for chromium and 93-108% for arsenic to demonstrate that the proposed method could be applied to determine chromium and arsenic species in sludge at different water area. The analytical results revealed that accumulation in sludge were predominantly inorganic chromium and arsenic, while the more toxic Cr(VI) and As(III) both existed in the high pollution water area. To sum up, different elemental species were presented which depend on the degree of water pollution and sampling location

Determination of mercury, chromium and arsenic species in sludge samples by HPLC-ICP-MS

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