Aqueous alkylation of anions for static headspace sampling with analysis by capillary gas chromatography‐mass spectrometry

Abstract

AbstractThe formation of ethyl derivative from anions and the conjugate bases of weak acids through the reaction with ethyl p‐toluenesulfonate in strongly basic aqueous systems was used as a precursor to analysis by static headspace sampling with capillary gas chromatography‐mass spectrometry. A host of materials are amenable to the technique including: cyanide, butyrate, caproate, fluoroacetate, iodide, and phenol. These analytes were used to study the performance of the system in relation to the behavior of commercially obtained ethyl derivatives. 18‐Crown‐6 (1,4,7,10,13,16‐hexaoxacyclooctadecane) effectively catalyzes the reaction which appears to require the presence of high concentrations (5 M) of a basic salt, such as potassium carbonate. A 1:1 (molar) mixture of dibasic and tribasic potassium phosphate effectively substitutes for potassium carbonate and provides improved performance for fluoroacetate while reducing interferences such as diethyl carbonate. Quantitative yields were obtained in the concentration range 0.05‐2 mM, except for cyanide which produced propionitrile with an efficiency of 55–80%. Fructose, at the 10% w/v level, exerted little influence upon the reaction. Calibration curves (selected ion monitoring) were linear between 0.001 and 1 mM. This approach extends the applicability of static headspace sampling and offers a potentially simple alternative to ion chromatography for complicated matrices. It should prove useful for confirming results obtained by other methods or for screening poorly characterized samples. © 1995 John Wiley & Sons, Inc.