Cold vapor atomic absorption spectrometric determination of mercury using sodium tetrahydroborate reduction and collection on gold

Determination of total mercury and methylmercury in biological samples by photochemical vapor generation

Cold vapor atomic absorption spectrometry (CV-AAS) based on photochemical reduction by exposure to UV radiation is described for the determination of methylmercury and total mercury in biological samples. Two approaches were investigated: (a) tissues were digested in either formic acid or tetramethylammonium hydroxide (TMAH), and total mercury was determined following reduction of both species by exposure of the solution to UV irradiation; (b) tissues were solubilized in TMAH, diluted to a final concentration of 0.125% m/v TMAH by addition of 10% v/v acetic acid and CH(3)Hg(+) was selectively quantitated, or the initial digests were diluted to 0.125% m/v TMAH by addition of deionized water, adjusted to pH 0.3 by addition of HCl and CH(3)Hg(+) was selectively quantitated. For each case, the optimum conditions for photochemical vapor generation (photo-CVG) were investigated. The photochemical reduction efficiency was estimated to be approximately 95% by comparing the response with traditional SnCl(2) chemical reduction. The method was validated by analysis of several biological Certified Reference Materials, DORM-1, DORM-2, DOLT-2 and DOLT-3, using calibration against aqueous solutions of Hg(2+); results showed good agreement with the certified values for total and methylmercury in all cases. Limits of detection of 6 ng/g for total mercury using formic acid, 8 ng/g for total mercury and 10 ng/g for methylmercury using TMAH were obtained. The proposed methodology is sensitive, simple and inexpensive, and promotes "green" chemistry. The potential for application to other sample types and analytes is evident.

Gas-diffusion flow injection determination of Hg(II) with chemiluminescence detection

A gas-diffusion flow injection method for the chemiluminescence detection of Hg(II) based on the luminol-H(2)O(2) reaction was developed. The analytical procedure involved the injection of Hg(II) samples and standards into a 1.50 M H(2)SO(4) carrier stream, which was subsequently merged with a reagent stream of 0.60% (w/v) SnCl(2) in 1.50 M H(2)SO(4) to reduce Hg(II) to metallic Hg. The gas-diffusion cell was thermostated at 85 degrees C to enhance the vaporisation of metallic Hg. Mercury vapour, transported across the Teflon membrane of the gas-diffusion cell into the acceptor stream containing 1.00 x 10(-4) M KMnO(4) in 0.30 M H(2)SO(4), was oxidised back to Hg(II). The acceptor stream was merged with a reagent stream containing 2.50 M H(2)O(2) in deionised water and then the combined stream was merged with another reagent stream containing 7.50 x 10(-3) M luminol in 3.00 M NaOH at a confluence point opposite to the photomultiplier tube of the detection system. The chemiluminescence intensity of the luminol-H(2)O(2) reaction was enhanced by the presence of Hg(II) in the acceptor stream. The corresponding increase was related to the original concentration of Hg(II) in the samples and standards. Under optimal conditions, the chemiluminescence gas-diffusion flow injection method was characterised by a linear calibration range between 1 microg L(-1) and 100 microg L(-1), a detection limit of 0.8 microg L(-1) and a sampling rate of 12 samples per hour. It was successfully applied to the determination of mercury in seawater and river samples.