Scaling up a microbore separation for semipreparative analysis: differential recoveries of radiolabeled amino acids

Application of a high-sensitivity microbore system designed to separate and quantify nonderivatized amino acids by anion exchange chromatography and amperometric detection for determination of amino acid-specific activities in biological samples requires high capacity to recover sufficient labeled material for adequate count statistics. Scale up from a low (25-1000 pmol) to a high (500-15,000 pmol) working range was achieved by use of a thick working electrode gasket to reduce sensitivity and eliminate peak splitting and tailing and by modification of the wash procedure to eliminate carryover. Analysis of recoveries of labeled amino acids revealed that specific amino acids are either selectively retained on the column or partially degraded during analysis and that assessment of purities of labeled compounds and metabolic labeling patterns requires careful analysis of recoveries of labeled compounds in the appropriate eluate fraction.