Development of Analytical Methods for Comprehensive Chemical and Physical Speciation of Arsenicals in Groundwater

Background/Need: The basis for understanding the abundance and distribution of arsenic in groundwater is reliable chemical analysis. Improvements in sample collection, sample pre-treatment, and on-site and off-site laboratory determination methods are sought to insure that information about arsenic is of high quality.

Objectives: The objective of this project was to develop improved analytical methods to better characterize the specific forms of arsenic that are present in the groundwater formations of the Fox River Valley (FRV).

Methods: The primary arsenic compounds present in FRV groundwater are the trivalent and pentavalent oxyacids, arsenious and arsenic acids, respectively. These compounds are found predominantly as dissolved species (liquid or solution phase) but also can be adsorbed to small particles and colloidal matter (solid or particulate phase). There are three primary steps in chemical analysis: (a) sample collection, (b) sample pre-treatment, and (c) analyte determination. For sample collection, we optimized an existing method based on solid-phase extraction. We then developed an improved sample pre-treatment method using iron-chelating preservatives to improve the preservation of the sample. For analyte determination, we expanded our existing potentiometric stripping method for on-site determination of both arsenious acid and arsenic acid, while we developed an improved method based on ion chromatography for off-site analyte determination. Additionally, we began studies of the particle-phase forms of the arsenic acids by field-flow fractionation.