| Trivalent inorganic arsenic compounds are considered to be more toxic than pentavalent inorganic compounds, and organo-compounds in the pentavalent state are less toxic than inorganic arsenic. In natural water, arsenic is mostly found in inorganic form as oxyanions of trivalent and pentavalent arsenic. Arsenic contamination in natural waters is a worldwide problem and has become a challenge for scientists. Recently, there has been an increasing interest in the field of arsenic speciation due to its unique nature and potential toxicity. Inductivity coupled plasma mass spectrometry (ICP-MS) is one of the most powerful methods for trace/ultra-trace elements analysis due to its outstanding advantages including high sensitivity, high sample throughput, wide linear dynamic range, multi-element detection and isotope analysis ability. The concentration of arsenic in drinking and natural waters is very low, sample pretreatment techniques aiming to preconcentrate the analytes can effectively improve the analytical performance. Therefore, exploring novel miniaturized, high sensitive and effective ICP-MS based hyphenated techniques is highly demanded for trace/ultra-trace elements and their speciation analysis. Because of its simple preparation, abundant surface chemical properties and good biocompatibility, hybrid organic-inorganic monolith, as a solid phase microextraction (SPME) absorbent, could be used to detect trace arsenic, followed by ICP-MS detection. Based on this background, we combined hybrid monolith SPME with ICP-MS. A mercapto hybrid organic-inorganic monolith was synthesized and optimized, and its extraction performance was examined as well. A hybrid monolith SPME-ICP-MS method was established for the detection of inorganic arsenic species in drinking and natural waters.1. The preparation and characterization of the mercapto hybrid monolithHybrid organic-inorganic monolith functionalized with mercapto groups was synthesized by sol-gel technology. Tetraethoxysilane (TEOS) was used as silica precursor and 3-mercaptopropyltrimethoxysilane (MPTMS) as organic functional moiety. Several modifications were conducted in the synthesis protocol in order to improve the resulting morphology of the monolith. The influence of several critical parameters, including the solvent category, reactant ratios, temperature, catalysts and hole-agent dosage, had been extensively studied. The hybrid silica monolith was characterized by various techniques, such as scanning electron microscopy, elemental analysis and diffused infrared spectroscopy. The results showed the hybrid monolith possesses particle agglomeration with interconnecting macropores. The diameters of the spheres and the flow-through pores was about 2μm and 5μm, respectively. The uniform particles in small size could offer high surface area for the retention of target analytes, whereas the macroporous structure would result in low backpressure and high permeability. The sulfur percentage was 10.6%, far higher than using traditional chemical bonding means.2. The application of the mercapto hybrid monolith in the separation of inorganic arsenic species in drinking and natural watersWe used the hybrid monolith as the extraction column in the in-tube SPME of inorganic arsenic in real water samples. By coupling the in-tube SPME to ICP-MS, we realized the detection of trace arsenic in water samples. Due to fast and quantitative retention of As(III) on the mercapto hybrid monolith, inorganic species of As(III) could be accurately determined without oxidation or subtraction, the total analysis took less than 15 min and the method was free from chloride interference. The limits of detection (LOD, defined as three times the signal-to-noise ratio) for As(III) was 0.21μg L-1, giving a signal enhancement factor of 50 by using the system. The recoveries for inorganic arsenic were in the range of 97-108%. The developed method was successfully applied to the speciation analysis of inorganic As(III) in drinking and natural waters. |
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