Determination of 4-chloro-2-methylphenoxyacetic acid residues in sediment using solid phase extraction and ultra-performance liquid chromatography-tandem mass spectrometry

4-chloro-2-methylphenoxyacetic acid (MCPA) is one of the high toxic herbicide that may cause the potential environmental risks for sediment. Thus, a simple and sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for determination of MCPA in sediment samples. The best conditions for analysis were as follow: sediment sample was treated by ultrasonic extraction with the acidified acetonitrile solution; the extract was then cleaned up with GCB-NH₂ solid phase extraction column; furthermore, the mobile phase consisting of acetonitrile and ultrapure water was used under gradient elution to isolate MCPA from impurities with HSS T3 column as the separator. The mass spectrometric detection was conducted in negative electrospray ionization with multiple reaction monitoring mode. The quantification of MCPA was performed using the matrix matched / external standard method. With the established method, an excellent linear relationship between chromatographic peak area and mass concentration of MCPA was obtained in the range of 1-100 μg/L (R² = 0.9997), and the quantitation limit (LOQ) sensitively reached 0.1 μg/kg. Under the fortified level of 0.1-5 μg/kg MCPA, the satisfactory relative recoveries (80%-108%) of MCPA in sediment were achieved with relative standard deviations of 3.6%-8.2%. During the establishment of UPLC-MS method, the contradiction between 'column retention' and 'mass spectrometry ionization' of MCPA was worked out by strengthening the binding forces between MCPA and chromatographic column. This method is rapid, accurate and sensitive, and is suitable for the analysis of trace MCPA residues in sediment.