Isolation of poly(propylene glycol)s from water for quantitative analysis by reversed-phase liquid chromatography

Procedures for the isolation of poly(propylene glycol)s (PPGs) from a water matrix have been developed. Solid-phase extraction with an octadecylsilica cartridge and elution with methanol or with a graphitised carbon black cartridge and elution with a mixture of dichloromethane–methanol (4:1) or liquid–liquid extraction with chloroform were all suitable for model samples. However, only liquid–liquid extraction was suitable both for model and real environmental samples. Methods for reversed-phase liquid chromatographic determination of PPGs based on derivatisation and ultraviolet or fluorescence detection have been developed. Four derivatisation agents [3,5-dinitrobenzoyl chloride, phenyl isocyanate, 1-naphthoyl chloride and 1-naphthyl isocyanate (NIC)] were tested. Only NIC was found to give good reproducibility as well as a satisfactory detection limit. Finally, a method with liquid–liquid extraction with chloroform, derivatisation with NIC and liquid chromatographic separation with fluorescence detection was established. The developed method shows a highly correlated linearity of the analytical signals of particular homologues within a wide concentration range (approximately from 0.01 to 10 mg l−1). The precision of measurements is satisfactory for homologues having 5–9 oxypropylene subunits and becomes worse with an increase in the number of oxypropylene subunits. The limit of detection is 2 μg l−1 for the majority of homologues. The method is suitable for the isolation and quantitative determination of PPGs in river water samples and as a tool for biodegradation testing.