Fresenius' Journal of Fresenius J Anal Chem (1994) 350:403-409 .... © Springer-Verlag 1994 Determination of trace amounts of highly hydrophilic compounds in water by direct derivatization and gas chromatography - mass spectrometry Claudio Minero, Marco Vincenti, Stefania Lago, Ezio Pelizzetti Dipartimento di Chimica Analitica, Universit~ di Torino, Via Pietro Giuria 5, 1-10125 Torino, Italy Received: 7 February 1994/Accepted: 18 March 1994 Abstract. A new procedure has been developed to de- rivatize a large set of highly hydrophilic substances ((poly) hydroxy and/or (poly)carboxylic acids, glycols and dihyd- roxybenzenes) directly in water. The key element of the method is the derivatizing agent used, n-hexyl chlorofor- mate, which proved to be much more effective than other alkyl and aryl chloroformates. Detection limits in the low gg/L range were found for most of the compounds studied, using positive ion chemical ionization mass spec- trometry as the detection technique. Calibration curves exhibited a good linearity over 2-3 orders of magnitude, so that quantitative determinations were possible. Among the experimental parameters tested, it was found crucial to introduce the chloroformate slowly and under sonica- tion. The whole derivatization procedure takes only 2-3 rain from sample collection to injection into the gas chromatograph. Introduction Few analytical procedures deal with the determination of highly hydrophilic organic substances, such as poly- hydroxy and/or (poly)carboxylic acids, in water, parti- cularly when they are present at trace levels [1, 2]. In contrast, the determination of hydrophobic organic sub- stances in aqueous solutions is a widely investigated field of analytical chemistry, particularly in environmental ap- plications [3-7]. Analytical procedures for this purpose include a preliminary extraction step, where the hydro- phobic substances are transferred from water to an or- ganic solvent, followed by clean-up and concentration steps and, lastly, injection into a chromatographic device, possibly a capillary column gas chromatograph interfaced to a mass detector [8, 9]. The problems for determining hydrophilic com- pounds are due, at least in part, to the difficulties encoun- tered in the two fundamental steps mentioned above, Correspondence to: C. Minero namely (i) the extraction of hydrophilic substances from the aqueous matrix and (ii) their chromatographic separ- ation and detection. Compounds exhibiting some am- phiphilic character (i.e. alkyl monocarboxylic acids) can be extracted from water with difficulty [10] but substan- ces such as polyalcohols and polycarboxylic acids have such a high water affinity that they do not partition into the organic phase to any extent. Derivatization chemically modifies the polar groups that prevent the extraction into a non-polar organic sol- vent. However reactions using the most common de- rivatizing agents (polyalkylsilanes, diazoalkanes, alkyl halides and perfluoroalkyl halides) must be performed under rigorously anhydrous conditions since the reagents are instantly hydrolyzed in water [11-13]. Thus these derivatizations require a preliminary step, in which the solvent is evaporated to dryness, before the reaction can be carried out on the residue or in a subsequently added organic solvent [14-16]. This procedure can lead to par- tial or total loss of some analytes and it is also time- consuming. Alternatively, extractive derivatizations can be utilized [ 17, 18]. Alkyl chloroformates have been used since 1976 to derivatize amino acids and amines in aqueous solution [19-22]. More recently, Hugek developed a series of inter- esting methodologies, which tolerate quite high percent- ages of water in the solvent, to derivatize alkyl carboxylic acids [23], 2-hydroxyalkyl carboxylic acids [24-26], amino acids [27, 28], amines [29] and phenolic acids [30] with alkyl chloroformates. It was found that the reaction occurring between 2-hydroxyalkyl carboxylic acids and methyl, ethyl or propyl chloroformates, transforms the carboxylic group into the corresponding ester (or into the alkoxycarbonyl ester, depending on the reaction condi- tions) and the hydroxyl group into the corresponding carbonate. The reaction can be carried out in a mixed solvent composed by acetonitrile, water, pyridine and an alcohol, although it was claimed that the highest derivat- ization yields were obtained using anhydrous solutions [24]. Hydroxyls which were not located in the c~position to a carboxylic group could not be derivatized with this procedure [24].