Determination of Ethephon Residue in Milk by Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry

An ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method with solid phase extraction (SPE) was established for the detection of ethephon residue in milk. In the sample pretreatment stage, formic acid solution was selected as the extraction solvent, and the extract was purified on an amino SPE column. The target compound was separated on a Waters Anionic Polar Pesticide column (150 mm × 2.1 mm, 5 μm) using gradient elution with a mobile phase consisting of 0.1% formic acid containing 50 mmol/L ammonium formate and acetonitrile. The detection was performed using electrospray ionization in the negative ion mode with multiple reaction monitoring, and the matrix-matched external standard method was used for quantification. The calibration curve for ethephon showed an excellent linearity (R² > 0.99) in the concentration range of 2 to 100 ng/mL, and the limit of detection and limit of quantification of this method were 0.5 and 1.0 μg/kg, respectively. At spiked concentration levels of 1.0, 2.0 and 10.0 μg/kg, the recoveries were between 92.50% and 113.76%, and the precision, expressed as relative standard deviation, ranged from 3.04% to 4.60%. In conclusion, the UPLC-MS/MS method has the advantages of high accuracy, specificity, and repeatability, and is very suitable for the determination of ethphon in milk.