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SummaryGas Chromatography with Mass Spectrometry (GCMS) was utilised to determine the penetration of prednisolone sodium phosphate into the aqueous humour of human volunteers undergoing routine cataract extraction. Detectable levels ofpred nisolone were measured in the aqueous humour within 15 minutes. Peak con centrations occurred between 90 and 240 minutes, and the steroid could not be detected in samples taken 10 hours or more after topical administration.

Prednisolone, dexamethasone and betamethasone were labelled with deuterium via a simple synthetic procedure and used as internal standards in the gas chromatographic/mass spectrometric analysis of the corresponding undeuterated compounds. The mass spectrometer was used in the negative chemical ionization mode, which gave fragmentation of the methoxime trimethylsilyl ether derivatives favourable for their quantification. The method was applicable to the quantification of synthetic corticosteroids contained in human aqueous humour in the 0.1-10-ng range.

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