Two analytical methods are presented for the determination of 2,4-D in oranges.
The screening procedure uses a commercial ELISA kit, designed for the determination of 2,4-D in water. Good semi-quantitative screening data were obtained provided that the standard solutions used to construct the calibration curve were prepared in blank orange extract. The limited quantification range of the kit was due to the narrow linear range and differences in response to 2,4-D when present as the free acid and as various esters.
A GC-MS confirmatory technique involved extraction of 2,4-D from oranges by homogenisation with methanol, filtration and esterification/transesterification with boron trifluoride-methanol. Recoveries for three spiking levels (0·2, 1·0 and 2·0 mg kg-1) for 2,4-D and 2,4-D isopropyl ester were within the range 75–120%.
In a small survey of retail oranges, 10 samples were screened using the ELISA kit and four were found to have >0·2 mg 2,4-D kg-1. All four residues were confirmed by GC-MS. The ELISA procedure involves approximately half the staff effort of the GC-MS procedure. © 1997 SCI.