LIQUID-CHROMATOGRAPHIC DETERMINATION OF FREE GLUTAMIC-ACID IN SOUP, MEAT PRODUCT, AND CHINESE FOOD - INTERLABORATORY STUDY

An interlaboratory study of the liquid chromatographic (LC) determinat ion of free glutamic acid in soup, meat product, and Chinese food was performed. Homogenized food samples were extracted with hot water, fil tered, and diluted, Aliquot portions were treated with N,N-dimethyl-2- mercapto-ethyl-ammonium chloride (DMMAC) and o-phtaldialdehyde (OPA) t o convert glutamic acid to a stable fluorescent complex. After LC sepa ration on a reversed-phase C-18 column with acetonitrile-phosphate buf fer (pH 7.0)-water (80 + 180 + 740, v/v) as mobile phase, glutamic aci d peaks were measured fluorometrically (excitation, 340 nm, and emissi on, 389 and/or 440 nm). Homocysteic acid was used as internal standard . Twelve samples (6 blind duplicates) containing about 0.3-1.3% (w/w) Of glutamic acid were analyzed singly by 12 laboratories, Results from one participant were excluded. Repeatability relative standard deviat ions (RSD(r)) varied from 1.3 to 4.5%, and reproducibility relative st andard deviations (RSD(R)) ranged from 4.1 to 7.1%, Average recovery o f glutamic acid determined at 6 levels was 101.5% (range, 98-106%).