Studies of organoarsenical speciation and reactivity in the environment: Development of novel optical and mass spectrometric methods.

摘要

The preservation, speciation, reactivity, and fate of arsenic compounds are of great interest in environmental systems with elevated arsenic concentrations. The research described herein details the development of novel methods for the study of arsenic quantification and reactivity in the environment.; Following the collection of a sample, the types of preservation measures taken are crucial in maintaining the sample integrity. An effective preservation method should prevent transformations (e.g., precipitation, adsorption, decomposition, etc.) during transport and storage. Because arsenic compounds vary widely in chemical and physical properties, sample preservation is particularly important. A new method is described in which 8-hydroxyquinoline-5-sulfonic acid (8-HQ-5-SA) was found to be an effective preservative for inorganic arsenicals in natural water samples. Unlike methods currently in practice, the 8-HQ-5-SA method accurately preserved the arsenic speciation for a period of 64 days. Additionally, a method based on solid-phase extraction was developed that also improved upon the figures of merit of previously reported methods.; The development, optimization, and application of novel methods for the unequivocal identification and quantification of 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone) and p-arsanilic acid (p-ASA) are described. The, Roxarsone method is based on capillary gas-liquid chromatography with parallel quadrupole ion-trap mass spectrometric and pulsed flame photometric detection. Roxarsone, dimethylarsinic acid, and monomethylarsonic acid are quantified in complex matrices at low parts-per-billion (mug/L) levels. Analytes are derivatized to their cyclic dithiaarsenolines with 1,3-propanedithiol and extracted from the sample matrix by solid-phase microextraction (SPME). The method was applied to several fortified environmental surface water samples where the average recovery for Roxarsone was 103 +/- 10.9%. The p-ASA method is based on sequential injection-long pathlength absorbance spectrophotometry (SI-LPAS) that exploits the selective reactivity of p-ASA with p-dimethylaminobenzaldehyde. Optimal reaction conditions were studied, namely reagent and sample volumes, reagent concentration, reaction time, reaction temperature, solution pH, and flow rate. For authentic surface water samples the average recovery was 100.5 +/- 13.4%.; The reactivity of arsenicals in the environment is an important aspect in understanding the ultimate fate of these toxic compounds. To better understand the types of reactions volatile arsines undergo, a novel kinetics chamber was designed, fabricated, and tested. Volatile arsenicals were generated in situ and then introduced into a quartz chamber located inside a gas chromatograph, where the atmosphere was monitored by a quadrupole ion-trap mass spectrometer. The thermal decomposition of the generated arsine in a helium atmosphere was determined to be a first-order reaction using an integral curve fitting method.