DETERMINATION OF ARSENOBETAINE, ARSENOCHOLINE, AND TETRAMETHYLARSONIUM CATIONS BY LIQUID-CHROMATOGRAPHY THERMOCHEMICAL HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY

A novel high-performance liquid chromatography-atomic absorption spectrometry (HPLC-AAS) interface based on thermochemical hydride generation has been developed and optimized for the determination of arsenobetaine [(CH3)3As+Ch2COOH], arsenocholine [(CH3)3As+CH2CH2OH], and tetramethylarsonium [(CH3)4As+] cations. In this quartz Interface, the methanolic HPLC eluent was nebulized by thermospray effect and pyrolyzed in a methanol/oxygen kinetic flame and the analytes were thermochemically derivatized to the hydride derivative in the presence of excess hydrogen. The volatile derivative was then transported to a cool diffusion H2/O2 flame atomizer. The fact that arsenic pentoxide was also derivatized, and that no signal was observed In the absence of postthermospray hydrogen or the absence of cool diffusion flame, corroborated the thermochemically mediated arsine-generation mechanism. Factorial models predicting the performance of the interface at different levels of five selected variables suggested that (a) both reverse- and normal-phase HPLC eluents were compatible with the interface and (b) the performance of this system was relatively insensitive (less than 50% variation in response) to changes over wide ranges in the operating parameters. At concentrations up to 10-fold excess, potential interferents [(CH3)3S+, (CH3)3Pb+] did not affect, significantly, the postulated thermochemical hydride generation (THG) process. However, a 10-fold molar excess of (CH3)3Se+ decreased the response of the analyte by 48%. Virtually identical responses were observed for equimolar amounts of tetramethylarsonium, arsenocholine, arsenobetaine [As(-III)], and dimethylarsinic acid [As(III)]. Arsenic pentoxide [As(V)] was detected with 75% efficiency, relative to the response of the organoarsenic compounds. The analytes were separated isocratically in a cyanopropyl bonded phase HPLC column, using a methanolic eluent containing 30% (v/v) diethyl ether, 1% (v/v) acetic acid, and 0.05% (v/v) triethylamine. The absolute limits of detection for the arsenobetaine, arsenocholine, and tetramethylarsonlum cations were 13.3, 14.5, and 7.6 ng, respectively. The low purchase and operating costs of this interface coupled with its relatively low limits of detection and good reproducibility make it a candidate for routine HPLCAAS monitoring of these arsenic-containing species. © 1990, American Chemical Society. All rights reserved.