Tetramethyl ammonium perchlorate

Figure 1. Distribution of fermium as a function of applied voltage between mercury in a dropping mercury cathode and 0.1M tetramethyl ammonium perchlorate at pH = 2.4. The slope of the logarithmically transformed line indicates the number of electrons exchanged in the electrolysis reaction (24).

Because of the stability of most of the arsenic compounds of interest for speciation studies, nearly all work commences with homogenized, predominantly lyophylized, materials. Extraction of arsenic species from dry and finely ground samples is often performed with methanol/water/chloroform mixtures or just methanol (Luten et al., 1982 Francesconi et al., 1985 Momplaisir et al., 1991 Ballin et al., 1992 ). Methanol and phosphate buffer (1 1) extraction was applied with especially good results for methylated forms of inorganic arsenic (Arenas, 1991). Rather simple approaches are the solubilization of various types of organic materials by treatment with e.g. tetramethyl ammonium hydroxide (TMAH) at ambient temperature for the subsequent determination of inorganic arsenic and its metabolites (Stoeppler and Apel, 1984, Burow and Stoeppler, 1987) and the solubilization of As(lll) and As(V) by treatment with perchloric acid and Fe2(S04)3 at elevated temperatures with subseqent separation and determination of As(lll) and As(V) (Holak and Specchio, 1991). Some speciation procedures based on NaOH treatment will be described under Speciation procedures. 

The most commonly used quaternary ammonium salts are tetrabutylammonium perchlorate (TBAP), tetrafluoroborate (TBAT), the halides (TBACl, TBAB, and TBAI), and the corresponding tetraethylammonium salts, such as the perchlorate (TEAP), but also the tetramethyl- or tetrapropylammonium salts have been employed the former cannot undergo a base-promoted Hofmann elimination. However, evidence has been found for the formation of trimethylammonium methylide [460]. In nonpolar solvents it may be necessary to employ tetrahexyl- or tetraoctylammonium salts. The tetraalkylammonium ions are soluble in many nonaqueous media, and they may be extracted from an aqueous solution by means of chloroform or methylene chloride [461,462], and tetraalkylammonium salts may thus be prepared by ion extraction [462]. Tetrakis(decyl)ammonium tetra-phenylborate is soluble even in hexane [442,443]. 

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