Simplified in-line sample preparation for amino acid analysis in carbohydrate containing samples

This report describes a new, automated chromatographic procedure eliminatin g carbohydrates from amino acid samples prior to their analysis by anion-ex change chromatography and integrated amperometric detection. In the first s tep, a sample is brought onto a short cation-exchanged column (trap column) in hydrogen form. Carbohydrates are passing through this column, while onl y amino acids are retained. Subsequently, the cation-exchange column. holdi ng the amino acid fraction, is switched in-line with the gradient pump and separator column. The mobile phase used at the beginning of the separation (NaOH; pH 12.7) transfers amino acids from the trap column onto the anion-e xchange column and the amino acid separation is completed without any inter ference by carbohydrates. All common amino acids are recovered following th e carbohydrate removal step. The average value of their recovery is 88.1%. The calibration plots were tested between 12.5 and 500 pmol (amounts inject ed). The mean value of correlation coefficients of calibration plots was ca lculated as 0.99. The mean value of relative standard deviations from five replicates was 3.9%. The usefulness of the method is illustrated with two c hromatograms of a carrot juice sample obtained before and after the in-line removal of carbohydrates. (C) 2001 Elsevier Science B.V. All rights reserv ed.