Ion-selective electrodes in organic analysis: Determination of alkyl halides via in situ generation of S-alkylisothiouronium salts

Low relative molecular mass alkyl halides, after in situ derivatization to the corresponding S-alkyl-isothiouronium salts in the presence of an excess of thiourea, were determined with a poly(vinyl chloride) membrane S-alkylisothiouronium-selective electrode based on S-butylisothiouronium tetraphenylborate. This membrane electrode exhibited Nernstian response in the range 1.0 × 10^-1-1.6 × 10^-4 mol dm ^-3 with an average cationic (positive) slope of 58.8 mV per concentration decade at 25°C. The electrode had a reasonably wide working pH range (6.5-8.5), fast dynamic response time (30 s-2 min), stable response for at least 2 months and high selectivity for the S-alkylisothiouronium ion in the presence of many inorganic and organic ions. The electrode functioned satisfactorily for the determination of primary and secondary alkyl halides, excluding alkyl fluorides.