INDIRECT CONDUCTIMETRIC DETECTION OF AMINO-ACIDS AFTER LIQUID-CHROMATOGRAPHIC SEPARATION

A liquid chromatographic method using indirect conductimetric detectio n is proposed for the determination of low levels of organic compounds , which does not require any special functional characteristics of the analyte. The signal detected is proportional to the molar concentrati on of the analyte and independent of its nature. The detector response is linearly dependent on analyte concentrations over at least three o rders of magnitude. The basis of the detection is to create a conducti ng background, which will decrease on elution of the organic compounds . The theory of the method is discussed, with special reference to the quantitative displacement of the conducting species of the mobile pha se from the column by the analyte on sample injection. The proposed me thod has been applied to study the chromatographic behaviour of twenty -one amino acids, where a 5-mu m Econosil CN column was used as the st ationary phase with a mixture of water-acetonitrile-tetrahydrofuran (7 0:20:3) containing 1 mM perchloric acid or trichloroacetic acid as the mobile phase. The proposed method allows as little as 10 ng of each a mino acid to be determined.