Determination of diphenylamine derivative by liquid ionization MS for the chemical substance safety test

Abstract

A method of analyzing new chemicals in fishes for the safety test was investigated using a liquid ionization (LI) mass spectrometer. The analyte used as one of the new chemicals was 2,2',4'-trimethyl-4-methoxydiphenylamine (TMMD). The LI method is applicable to analysis of a mixture without a complicated procedure for separating analytes from the matrix-like fish components. Two simple procedures for sample preparation were examined according to the concentration of TMMD added to carp. The procedures were as follows: The analyte TMMD with 3,3'-dimethyldiphenylamine (DMD) as an internal standard was added to minced fish (30 g), then the analyte and the internal standard were extracted with 80 ml of acetonitrile in a homogenizer and the extract was filtered to remove insoluble materials. In the concentration range of 3.5~35 μg TMMD/g fish, 10 ml of the filtrate (total volume, 100 ml) was concentrated to 1 ml by evaporation. This was named the single extraction procedure. In the concentration range of 0.35~3.5 μg TMMD/g fish, 50 ml of the filtrate (total volume, 100 ml) was concentrated to 8 ml of aqueous solution. Two ml of ethylacetate was added to extract TMMD with DMD and the ethylacetate layer was concentrated to 0.5 ml. This was named the two step extraction procedure. The LI mass spectra exhibited protonated molecules (MH+) of TMMD and DMD as well as several peaks originating from the carps. The calibration curve calculated from the ratio of total MH+ ion of TMMD to that of DMD versus the concentration ratio is linear. The determination limit of TMMD in carp was about 0.3 μg/g. This result suggests that LI-MS is useful as a rapid method for the safety test. © 1990, The Japan Society for Analytical Chemistry. All rights reserved.