Determination of methyl anthranilate in food samples by coupling stopped-flow mixing technique and time-resolved luminescence detection.

A sensitive and fast approach for the determination of methyl anthranilate in grape must and honey samples, using time-resolved luminescence measurements, has been reported for the first time. The method involves the alkaline hydrolysis of the ester to anthranilic acid and the formation of a chelate with terbium(III) and tri-n-octylphosphine oxide in presence of Triton X-100. Kinetic and equilibrium measurements were obtained in 0.1 and 15 s, respectively, by using a stopped-flow mixing technique. The dynamic ranges of the calibration graphs of the kinetic and equilibrium methods were 21.9 nmol/L-29.2 micromol/L and 19.7 nmol/L-21.9 micromol/L, respectively, and the detection limits were 7.3 and 6.6 nmol/L, respectively. The precision, expressed as relative standard deviation, was less than 3%. Although both-kinetic and equilibrium methods exhibited very similar analytical features, only the better selectivity of the former allowed the content of methyl anthranilate to be determined in the samples, as the initial rate measurements avoided the negative effect that the sample matrix caused in the equilibrium measurements. The analytical recoveries obtained by applying the kinetic method to the analysis of grape must and flower honey samples were in the range 92.5-105.0%.