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Solid-phase extraction has become one of the most commonly used techniques for preconcentration of analytes from environmental samples. In the standard use of solid sorbent phases the extracted pollutants are subsequently eluted with a suitable organic solvent before chromatographic analysis. An alternative to this procedure is analysis of the adsorbed and concentrated pollutants by direct application of a spectroscopic method (fluorimetry or absorptiometry) to the phase. Although this method cannot be expected to give results as precise as those given by chromatographic methods, it might have valuable applications, particularly for "on site" pollution monitoring. This paper reports an evaluation of the capability of the method for the spectrophotometric detection of BTX (benzene, toluene, xylenes) in aqueous media and in contaminated atmospheres, with polydimethylsiloxane (PDMS) as sorbent. The tests performed, with the estimated detection limits, indicate that the method is relatively simple and easy to operate and sensitive enough for application to the monitoring of pollution both in water and in air in an industrial ambient atmosphere.

The rate coefficients for the reaction with diazodiphenylmethane in methanol, ethanol, isopropyl alcohol, t-butyl alcohol, 2-methoxyethanol, 2-n-butoxyethanol, dimethyl sulfoxide, ethyl acetate, and toluene at 30" and the pK, values in water, 50% ethanol-water, and 80% 2-methoxyethanol-water of 18 substituted acetic and propionic acids have been determined. A further 14 acids have been studied to a more limited extent. The effect of substitution has been estimated by linear free energy relations. The reaction constants for the ionization reaction are almost independent of the medium. This is interpreted as being due to the field effect of the proximate polar substituents passing through the molecular cavity almost alone. The occurrence of steric inhibition of solvation causing acid weakening for bulky multisubstitution is confirmed. The reaction constants for the esterification reaction are affected by the solvent. This is attributed to dependence on solvation of the transition state.Canadian Journal of Chemistry, 46, 2929 (1968) IntroductionAs part of our examination of the mode of the transmission of polar effects, it was considered important that transmission in aliphatic systems and their dependence on the medium should be studied. Suitable reactions were considered to be the esterification of carboxylic acids with diazodiphenylmethane (DDM) and their ionization. The system chosen for this study was a series of singly substituted acetic and 3-substituted propionic acids, together with a number of more highly substituted acids. The intention was to obtain a comprehensive series of results for the esterification and ionization reactions for this model system in order to be able to discuss the influence of the substituents on reactivity in aliphatic systems.Taft in his pioneering studies (1) made a distinct advance in understanding polar substituent effects in aliphatic systems. The aliphatic polar substituent constants, a*, which had been separated from the accompanying steric effects in ester hydrolysis, were found to correlate, among other reactions, the ionization of aliphatic carboxylic acids in water at 25" (1) and the esterification of the acids with DDM in ethanol at 25" (2). Hoefelmeyer and Hancock (3) and Bowden, Chapman, and Shorter (4) have extended these correlations to the esterification of aliphatic

SummaryDesorptionlchemical ionization mass spectrometry (D/CI.-MS.) is a recently developed technique especially indicated for highly polar and non volatile compounds. Various naturally occurring glycosides such as saponins, iridoid and secoiridoid glycosides, cardenolides and flavone-0-glycosides have been investigated by this method. All the measurements were carried out on underivatized compounds. In addition to the structural informations generally furnished by field-desorption mass spectrometry (molecular ion and sugar sequence), the molecular ion and pertinent fragments of the aglycone could also be obtained.

In this paper we introduce a novel procedure for the analysis of insect juvenile hormones and describe the principal steps involved in this method. Due to the low concentration of these hormones in insects, careful purification of samples before analysis is necessary. Biological samples are purified by solvent partition and reversed phase high pressure liquid chromatography, then analysed by gas chromatography mass spectrometry using a spectrometer equipped with a data acquisition system. By this procedure lOOpg of insect juvenile hormone could be detected in biological extracts.