Rapid quality control analysis of C-13-enriched substrate synthesis by isotope ratio mass spectrometry

There is a growing interest in the use of C-13-enriched substrates to inves tigate metabolic processes in humans. The non-invasive nature of C-13 breat h tests makes them attractive to clinicians, particularly because they can be safely used in children. The availability of suitable C-13-enriched subs trates can limit the application of this biotechnology. We have used isotop e ratio mass spectrometry to assay the chemical purity and isotopic enrichm ent of substrates that were synthesised to study gut transit and colonic fe rmentation. Lactose ureide and lactose [C-13]ureide were synthesised by aci d-catalysed condensation of lactose and urea or C-13 urea, respectively. Gl ucose ureide and glucose [C-13]ureide were synthesised by similar methods b ut required an additional purification step to remove urea. of crystallisat ion. Substrates were analysed by standard analytical techniques and combust ion isotope ratio mass spectrometry for carbon and nitrogen content and C-1 3-enrichment. Monitoring the C/N ratio proved to be a sensitive assay of ch emical purity. Analysis of the percentage composition of C and N (and hence O + H) suggested that lactose ureide crystallises as the dihydrate. It was synthesised with similar to 99% chemical purity and with the theoretical e nrichment. Glucose ureide was synthesised with similar to 98% chemical puri ty but with lower than theoretical enrichment. Copyright (C) 2001 John Wile y & Sons, Ltd.