The Development Of A Miniature Long-Optical Path Atomic Absorption Spectrometer For Mercury Speciation

Mercury is a toxic heavy metal which has significant impact on human health as well as ecological environment. Its toxicity depends not only on the total concentration, but also on its chemical forms. Inorganic and methyl mercury species are the major existing forms in the environment. Therefore, it is highly desireable to develop a simple and rapid analytical method for the determination of inorganic and methyl mercury species in environmental samples. Currently, the hyphenation of chromatography or capillary electrophoresis with bulky atomic spectrometric instrumentations is the major analytical approach for mercury speciation. However, nowadays we have to frequently encounter field analytical tasks caused by accidental pollution incidents. In this respect, the bulky instruments are usually out of choice. Due to the particular requirements of field analysis, the development of miniaturized instrumentations for specific analytical purposes has been one of the most important momentum.In the present work, a miniature long-optical path atomic absorption spectrometric system is developed with dielectric barrier discharge (DBD) low temperature micro-plasma as atomizer. Mercury and methylmercury vapor is generated in a sequential injection system. It is directed to flow through a gas-liquid separator, a glass wool moisture-removal microcolumn and the DBD atomizer, and finally transported into the long optical-path detection cell for quantitative analysis by atomic absorption spectrometry. The atomization of hydride is completely achieved by the DBD micro-plasma atomizer, and the detection sensitivity of the present system is highly improved by the increase of absorption optical path (1.1 mm i.d.,400 mm length). Meanwhile, a glass wool moisture-removal microcolumn integrated in the flow system effectively eliminates the influence of concomitant moisture during the vapor generation process, which avoids the drift of absorbance baseline. The absorbance arising from mercury is recorded by turning off the DBD atomizer, while the total absorbance from both mercury and methylmercury is measured by turning on the DBD atomizer. Further experiments demonstrated satisfactory additivity for the absorbance arising from inorganic and methyl mercury, which provides basis for the determination of mercury and methylmercury. With a sampling volume of 1.0 mL, detection limits of 0.3 μg L-1 and 0.4 μg L-1 are achieved respectively for inorganic and methyl mercury, along with RSD values of < 4%. The reliability of the present system is demonstrated by analyzing certified reference materials and real samples for mercury speciation.