Isolation of bicarbonate from equine urine for isotope ratio mass spectrometry†

Abstract

Sodium bicarbonate administration to horses prior to competition in order to enhance the buffer capacity of the organism is considered as a doping offence. The analysis of the isotopic composition of urinary bicarbonate/CO2 (TCO2) may help to identify an exogenous bicarbonate source, as technical sodium bicarbonate exhibits elevated δ13C values compared with urinary total carbon. The isolation of TCO2 from 60 equine urine samples as BaCO3 followed by an isotopic analysis shows a significant variability of δ13C for TCO2 of more than 10 ‰. The δ13C of total carbon and TCO2 seem to reflect different proportions of C3 and C4 plant material in the diet. The isotopic analysis of different mixtures of technical NaHCO3 and equine urine shows that TCO2 can be easily isolated without major isotopic fractionation; however, attention has to be paid to the storage time of urine samples, as a shift of δ13C of TCO2 to lower values may occur. †Revised version of the paper presented at the 27th Annual Meeting of the German Association for Stable Isotope Research (GASIR), 4–6 October 2006, Freiberg, Germany.