Ion chromatography with suppressed conductivity detection: recoveries of 14C-labeled metabolites

Suppressed conductivity detection, developed for use with ion chromatography, might be useful to assay specific activities of organic acids after metabolic labeling. Because the suppressor reduces background conductivity by acid-base neutralization and removal of ions from the eluent, it could influence recoveries and apparent retention times of labeled compounds. Elution times of 14C-labeled glucose and neutral amino acids, compounds not detected by conductivity, from the analytical column were found to be similar to those of lactate and acetate. When the suppressor was connected to the HPLC system in the recycle mode, the apparent elution times of amino acids increased and various organic acid fractions would be contaminated. When the suppressor was used in the external water mode, the labeled neutral amino acids and portions of acidic amino acids were recovered in the waste fraction; this indicated that recoveries of total 14C in the analyte fraction would be incomplete if the loss were not taken into account. Thus, the procedure to insert the suppressor into the system influences the apparent retention times and the recoveries of labeled amino acids in the analyte fraction; labeled metabolites not detected by conductivity can cause serious errors in specific activities of organic acids and should be removed from the sample prior to analysis.