A New Matrix Certified Reference Material for Measurement of Chlormequat Chloride and 2,4-Dichlorophenoxyacetic Acid Residues in Cucumber

A novel cucumber pulp certified reference material (CRM) was prepared for the analysis of plant growth regulator residues, specifically chlormequat chloride (CCC) and 2,4-dichlorophenoxyacetic acid (2,4-D). The matrix CRM candidates were prepared by cucumber pulping, spiking, homogenizing and subpackaging. A reference method of liquid chromatography tandem isotope dilution mass spectrometry (ID-LC-MS/MS) was established for simultaneous measurement of mass fractions of CCC and 2,4-D in cucumber pulp. Interlaboratory value assignment of CCC and 2,4-D in the cucumber pulp CRM was performed using the ID-LC-MS/MS method. The certified values with expanded uncertainties (coverage factor k = 2) were assigned to be 4.1 mg/kg ± 0.4 mg/kg for CCC, 2.0 mg/kg ± 0.2 mg/kg for 2,4-D. Homogeneity assessment was performed on fifteen randomly selected units, and statistical analysis confirmed the CRM's homogeneity for both CCC and 2,4-D, both between and within packages. The long-term stability of the CRM at -20 °C storage condition and short-term stability at 30 °C were monitored for 14 months and nine days, respectively, and no significant trend differences were observed. The uncertainty contributions from characterization, homogeneity and stability were taken into account in uncertainty evaluation. The CRM was officially certified and registered under the number GBW(E)100932 by the State Administration for Market Regulation of the P. R. China.