7. ANALYTICAL METHODS
The purpose of this chapter is to describe the analytical methods that are available for detecting, measuring, and/or monitoring chlorine dioxide and chlorite, its metabolites, and other biomarkers of exposure and effect to chlorine dioxide and chlorite. The intent is not to provide an exhaustive list of analytical methods. Rather, the intention is to identify well-established methods that are used as the standard methods of analysis. Many of the analytical methods used for environmental samples are the methods approved by federal agencies and organizations such as EPA and the National Institute for Occupational Safety and Health (NIOSH). Other methods presented in this chapter are those that are approved by groups such as the Association of Official Analytical Chemists (AOAC) and the American Public Health Association (APHA). Additionally, analytical methods are included that modify previously used methods to obtain lower detection limits and/or to improve accuracy and precision.
No methods for determining chlorine dioxide in biological materials were located. Most studies concerning human health effects measure the concentrations of chlorine dioxide in the air or in water. The measurement of chlorine dioxide in biological materials is not commonly used because of the rapid conversion of chlorine dioxide to chlorine-containing metabolites, such as chlorite and chloride ions. Abdel-Rahman et al. (1980b) developed a method to quantitatively and qualitatively measure the metabolites of chlorine dioxide (e.g., ClO2-, and ClO-) in biological fluids. These biomarkers can be used to indirectly measure chlorine dioxide exposure. The concentration of residual chlorite ion in vegetables and eggs treated with sodium chlorite was determined by UV-ion chromatography (Suzuki et al. 1997). Sodium chlorite was extracted with water and cleaned-up using C18 cartridge. The detection limit of sodium chlorite in vegetables and eggs was 1 mg/kg with recoveries of 90–100%.
Chlorine dioxide has been measured in air and water. Methods for determining levels in the air include spectrophotometry and ion chromatography. Environmental analyses of chlorine dioxide in water are
CHLORINE DIOXIDE AND CHLORITE 7. ANALYTICAL METHODS
performed using electrochemical, chromatographic, or spectrophotometric methods. Analytical methods for the determination of chlorine dioxide in environmental samples are given in Table 7-1. Ion chromatography may also be used to analyze the inorganic disinfection by-products of chlorine dioxide (i.e., chlorite ions) in an analogous manner using EPA Method 300.0 (Pfaff and Brockhoff 1990). Atmospheric chlorine dioxide may be sampled by pulling a given volume of air through a toxic gas vapor detector tube. The tube contains chemicals that react only with chlorine dioxide. If chlorine dioxide is present, the indicator chemical in the tube will change color. The concentration of the gas or vapor may be estimated by either the length-of-stain compared to a calibration chart or the intensity of the color change compared to a set of standards (EMMI 1997). Diffusive samplers have been used to monitor chlorine dioxide and chlorine in workplace air. In this technique, workplace air is diffused into an absorbing solution of neutrally buffered potassium iodide. In the absorbing solution, chlorine dioxide and chlorine are reduced by iodide ions to chlorite and chloride ions, respectively. The formed ions are then separated and quantified by ion chromatography. The analytical detection limits have been found to be 0.02 and 0.07 ppm for chloride and chlorite ions, respectively (Björkholm et al. 1990). Spectrophotometry (or colorimetry) has been used to measure chlorine dioxide in water using indicators that change colors when oxidized by chlorine dioxide. Spectrophotometric analyzers determine the...