Beaumont, Claire; (1997) Complex mixture analysis by liquid chromatography-mass spectrometry. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The combination of liquid chromatography with mass spectrometry is a valuable tool for the identification and quantification of compounds in crude biological matrices. This thesis describes the application of a variety of mass spectrometric techniques to three different analytical problems; The metabolic fate of Hoe 127490, a compound which shows potential as a sulfonyl urea herbicide, was investigated. Rats were dosed with Hoe 127490 and liquid chromatography-tandem mass spectrometry (LC/MS/MS) with electrospray (ES) ionisation was employed to analyse a sample of urine from the treated animals. No pretreatment of the urine sample was performed prior to injection. Numerous metabolites of Hoe 127490 were identified and a metabolic pathway is proposed. A semi-automated LC/MS/MS method using atmospheric pressure chemical ionisation (APCI) was developed which allows the rapid identification of dipeptides in complex mixtures, in particular in protein hydrolysates. Protein hydrolysates which are used for nutritional purposes are complex mixtures of peptides and free amino acids and their analysis poses a considerable challenge. The LC/MS/MS method was applied to a sample of a casein hydroysate and fifty-two dipeptides were identified. Suggestions were also made into extending the method to allow the identification of larger peptides. A rapid assay for the quantification of a potential insecticide, SN 609369, in plasma samples by thermospray liquid chromatography-mass spectrometry (LC/MS TSP) was developed. Sheep were dosed with SN 609369 and the level of the compound remaining in the animal's blood was monitored over a three week period. An earlier method of quantification had involved a lengthy extraction procedure followed by LC with ultraviolet detection. Sample analysis times were reduced from hours with this earlier method to minutes using LC/MS with selected ion recording. The necessity for a complex extraction procedure was also eliminated. The detection limits for SN 609369 using TSP, ES and APCI ionisation methods were compared.

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