title: Artefacts in organic acid analysis: occurrence and origin of partially trimethylsilylated 3-hydroxy-3-methyl carboxylic acids.
abstract: Previous reports of patients with 3-hydroxy-3-methylglutaric aciduria have described the occurrence of di-trimethylsilyl (TMS) and tri-TMS derivatives of 3-hydroxy-3-methylglutaric acid on analysis using gas chromatography and mass spectrometry, leading to difficulty in quantification and ambiguity in diagnosis. We have extracted organic acids from the urine of patients with 3-hydroxy-3-methylglutaric aciduria using a variety of procedures. Solvent extraction combined with hydrochloric acid/sodium chloride resulted in production of both di-TMS and tri-TMS derivatives of 3-hydroxy-3-methylglutaric acid and also mono-TMS and di-TMS derivatives of 3-hydroxyisovaleric acid. The effects were not abolished by heating. Use of sulphate-based reagents minimised artefact formation and use of DEAE-Sephadex anion exchange extraction resulted in single fully trimethylsilylated derivatives. Artefact formation during use of chloride-based reagents was abolished by pyridine added prior to trimethylsilylation. Chloride ions form adducts with hydroxyl groups in these 3-hydroxy-3-methyl carboxylic acids that prevent complete trimethylsilylation. Chloride-based reagents should be avoided in the solvent extraction of organic acids from physiological fluids or, if used, pre-treatment of the dried extract with pyridine is essential to avoid partial trimethylsilylation of 3-hydroxy-3-methyl carboxylic acids.
authors.affiliation: Paediatric Metabolism Unit, Department of Child Health, St George's Hospital Medical School, Cranmer Terrace, SW17 0RE, London, UK.
authors.forename: M G
authors.initials: MG
authors.lastname: Jones
authors.forename: R A
authors.initials: RA
authors.lastname: Chalmers
mesh_terms: D016477:Artifacts; D002852:Chromatography, Ion Exchange; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D015093:Meglutol / Q000652:urine*; D007652:Oxo-Acid-Lyases / Q000172:deficiency; D014297:Trimethylsilyl Compounds / Q000737:chemistry
chemical_list: D014297:Trimethylsilyl Compounds; D015093:Meglutol; D007652:Oxo-Acid-Lyases; C021410:3-hydroxy-3-methylglutaryl-coenzyme A lyase