Online stable carbon isotope ratio measurement in formic acid, acetic acid, methanol and ethanol in water by high performance liquid chromatography–isotope ratio mass spectrometry Original Research Article

A suitable analysis condition was determined for high performance liquid chromatography–isotope ratio mass spectrometry (HPLC–IRMS) while making sequential measurements of stable carbon isotope ratios of δ13C in formic acid, acetic acid, methanol and ethanol dissolved in water. For this online column separation method, organic reagents are not applicable due to carbon contamination; thus, water and KH2PO4 at low concentrations were tested as mobile phase in combination with a HyPURITY AQUASTAR™ column. Formic acid, acetic acid, methanol and ethanol were separated when 2 mM KH2PO4 aqueous solution was used. Under the determined analysis condition for HPLC–IRMS, carbon concentrations could be measured quantitatively as well as carbon isotope ratio when carbon concentration was higher than 0.4 mM L for each chemical.