Indirect conductometric detection of amino acids after liquid chromatographic separation. Part II. determination of monosodium glutamate in foods

A liquid chromatographic (LC) method using indirect conductometric detection is proposed for the determination of monosodium glutamate in foods, where a conductivity detector is used for detection. It involves the use of a 5-μm Econosil CN column as the stationary phase with a mixture of water, acetonitrile and tetrahydrofuran containing 1 mM perchloric acid or trichloroacetic acid as the mobile phase. Pre-column or post-column derivatization of the amino acid to increase the sensitivity of detection is not required. The proposed method employs a short Dowex 50W-X8 (H+) column for the sample clean-up prior to LC determination. Freezedrying is used for pre-concentration and the residue is redissolved in the LC mobile phase before measurement. The peak due to glutamic acid was well separated from the solvent peak and those from other amino acids or food components. The calibration graph is linear from 0 to 500 μg/ml of sodium glutamate. The R.S.D. for 10-replicate measurements of the sodium glutamate content of an oyster flavoured sauce containing 3.00% (m/m) of the compound was 1.8%. The proposed method has been applied to determine monosodium glutamate, down to the low level of 0.007% (m/m), in a variety of food samples.