INDIRECT CONDUCTOMETRIC DETECTION OF AMINO-ACIDS AFTER LIQUID-CHROMATOGRAPHIC SEPARATION .2. DETERMINATION OF MONOSODIUM GLUTAMATE IN FOODS

A liquid chromatographic (LC) method using indirect conductometric det ection is proposed for the determination of monosodium glutamate in fo ods, where a conductivity detector is used for detection. It involves the use of a 5-mu m Econosil CN column as the stationary phase with a mixture of water, acetonitrile and tetrahydrofuran containing 1 mM per chloric acid or trichloroacetic acid as the mobile phase. Pre-column o r post-column derivatization of the amino acid to increase the sensiti vity of detection is not required. The proposed method employs a shea Dowex 50W-X8 (H+) column for the sample clean-up prior to LC determina tion. Freezedrying is used for pre-concentration and the residue is re dissolved in the LC mobile phase before measurement. The peak due to g lutamic acid was well separated from the solvent peak and those from o ther amino acids or food components. The calibration graph is linear f rom 0 to 500 mu g/ml of sodium glutamate. The R.S.D. for 10-replicate measurements of the sodium glutamate content of an oyster flavoured sa uce containing 3.00% (m/m) of the compound was 1.8%. The proposed meth od has been applied to determine monosodium glutamate, down to the low level of 0.007% (m/m), in a variety of food samples.