Preparation of a national reference material organochlorine pesticide mixture for residue analysis†

Feasibility studies were carried out for the preparation of a national reference pesticide mixture. Three mixtures containing 12 organochlorine pesticides were prepared. One was prepared volumetrically and two were prepared gravimetrically. α-HCH, γ-HCH, aldrin, dieldrin, endrin, 4,4′-DDD, 4,4′-DDT, 2,4′-DDT, α-endosulfan, β-endosulfan, heptachlor and heptachlor endo-epoxide were analysed in gravimetric mixtures, and except for heptachlor endo-epoxide, the same pesticides were analysed in volumetric mixtures. Short- and long-term stability tests of organochlorine pesticides were performed at 20 °C to determine transport behaviour and at +4 °C and −20 °C to determine behaviour under optimal storage conditions. The most stable temperature was considered −20 °C. There is no significant change in the concentration of the pesticides determined weekly and monthly in the mixtures over a period of 5 months. The uncertainty of these pesticides was calculated with respect to the uncertainty of homogeneity, short- and long-term stability, purity of standards, GC-MS calibration plot and uncertainty of characterization according to ISO Guide 17034. Consequently, the uncertainty results for α-HCH, γ-HCH, aldrin, dieldrin, endrin, 4,4′-DDD, 4,4′-DDT, 2,4′-DDT, α-endosulfan, β-endosulfan, heptachlor and heptachlor endo-epoxide were determined to be around 0.5, 0.5, 0.3, 0.2, 0.4, 0.6, 0.8, 0.7, 0.3, 0.3, 1.2 and 0.5 in gravimetric mixtures for 100 ppm. In volumetric mixtures, their uncertainties were determined to be 2.4, 3.1, 4.1, 2.7, 15, 2.8, 4.1, 3.9, 3.2, 3.6 and 12.6 for 80 ppm, respectively.