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Determination of Arsenic in Water by Potentially Portable Methodology

Arsenic contamination in groundwater is a worldwide problem. The existing portable field test kits can not provide accurate results when the arsenic concentration is around 10 μg L-1 or lower. This research first was focused on the development and validation of methods in which portable instrumentation, such as electrochemistry instruments or quartz crystal microbalances, could be used to accurately determine arsenic concentrations in water even when the concentration is below 10 μg L-1. A modified anodic stripping voltammetry (ASV) and cathodic stripping voltammetry (CSV) method with measurement at a microarray electrode manufactured by TraceDetect Inc. was developed. When the ASV method with a gold electrode was applied for real water analysis, the detection limit of arsenite was 2.2 μg L-1, and for arsenate was 0.13 μg L-1. In the CSV method the more commonly used hanging mercury drop electrode was replaced with a mercury film array electrode. Under the optimum condition, this method had a detection limit for arsenite of 0.58 μg L-1 and for arsenate of 2.7 μg L-1. A method for the determination of arsenic using a quartz crystal microbalance was developed in which the crystal surface was modified in situ by dithiolthreitol, an arsenite-selective ingand. The method was applied to real water sample analysis with a limit of 0.6 μg L-1. The second was concerned with an investigation of the kinetics of the reactions that are the basis of several currently available field test kits (as exemplified by the Hach Kit) using inductively coupled plasma mass spectrometry (ICP-MS) with the goal of improving the performance of the test kit. The time for arsine gas reaches to the maximum concentration in the headspace of the vessel was about 60 min without continuous stirring and only 20% of arsenic was absorbed on the test strip. To speed up the arsine generation, continuous stirring condition can be applied. It also made more arsine absorbed on the test strip. The SEM study proves the structure of the darker colored compound. For the lighter colored compounds, the information is not enough to make a conclusion.
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