Simultaneous determination of six auxin plant growth promoters in agricultural products by liquid chromatography tandem mass spectrometry (LC-MS/MS)

Abstract

A highly sensitive and specific method for simultaneous determination of six synthetic auxins (4-chlorophenoxyacetic acid (4-CPA), 2-methyl-4-chlorophenoxyacetic acid (MCPA), 1-naphthalene acetic acid (NAA), 2-napthoxyacetic acid (NOA), indole-3-propionic acid (IPA), indole-3-butyric acid (IBA)) were developed using a QuEChERS-based sample extraction followed by an LC-MS/MS analysis. The method was validated and proved as meeting the AOAC International requirements for specificity, sensitivity, and accuracy in the range of 3 and 200 µg/kg. LOD and LOQ of all analytes were at 1 µg/kg and 3 µg/kg, respectively. The recoveries of six synthetic auxins were from 78.9% to 96.4% and the repeatability relative standard deviations were below 12.6%. The method was applied to simultaneously determine the content of 4-CPA, MCPA, NAA, NOA, IPA, IBA in vegetables, tubers, and fruits samples collected from different markets in Hanoi (Mai Dich, Dan Phuong, Giap Bat, Bach Mai, and Nga Tu So). MCPA was detected in 22/30 vegetable samples (3.0 ÷ 7.1 µg/kg), 9/30 tuber samples (3.2 ÷ 3.7 µg/kg); 4-CPA was detected in bean sprouts in the range from 23 to 75 µg/kg which exceeded the Maximum Residue Levels (MRL) of 10 µg/kg set by European Commission.