A sample preparation method for measuring recovery is to add the active ingredient of a solution or standard to a solid blank sample. Model formulations were prepared by various addition methods, and recoveries and physical properties were measured. The results showed no differences in the recoveries depending on the addition method, but the variabilities and physical properties differed. It was suggested that the most appropriate method was to add ≥50 mg/batch when the standard was added directly, or ≥2 mL/batch when the solution was added (solvent was removed), followed by grinding.

In measuring the recovery of pesticide formulations, when blank samples are not available, the active ingredient is added to the material to be analyzed; however, international guidelines do not provide details of the procedures. For the four active ingredients for which the CIPAC (Collaborative International Pesticides Analytical Council Limited) method have been established, recoveries from formulations with adding the equivalent of from 20 to 140% were measured. Since RSD (Relative standard deviation) was found to be increased at low addition levels, a single concentration between 50% and 100% equivalents was considered to be sufficient. Substances that interfere with the analysis of the active ingredient, equivalent to 40–100% of the active ingredient, were added to the formulation, and their effect on trueness was measured.