I. Preparation of Standards
1. Prepare a 10 mg/mL stock solution of aldicarb (Riedel de Haen) in methanol e.g. 100 mg aldicarb qs to 10 mL. Prepare a 20 ppm stock solution by diluting the 10 mg/mL stock solution 1:500 (20 mL of 10 mg/mL aldicarb qs 10 mL with methanol).
2. Label four 10 mL volumetrics: 0 standard, standard 1, standard 2, standard 3.
3. Add the appropriate volume of the 20 ppm aldicarb stock to each volumetric:
4. Add 20 mL of (aldicarb-free) oil to be used for the standard into all four volumetrics.
5. QS each volumetric to 10 mL with methanol. Invert repeatedly to mix thoroughly.
II. Preparation of samples
1. Dilute oil samples to be tested 1:500 in methanol e.g. 100 mL of oil into 50 mL of methanol.
III Assay protocol
1. Dilute standards (part I) and samples (part II) 1:20 in assay kit diluent e.g. 100 uL of methanol dilution plus 1.9 mL of assay kit diluent.
2. Perform the aldicarb protocol as described in the package insert substituting the prepared standards for the kit standards.
3. Determine the concentration of aldicarb in unknowns from a standard curve derived from the standards using the following concentration values. This will give you the concentration (ng/mL = ppb) of aldicarb in the diluted sample.
4. The actual concentration of aldicarb in undiluted oil is determined by multiplying the assay value by 10,000. For example, a sample that gives an assay value of 1 ppb actually contains 10 ppm of aldicarb:
1 ng/mL x 10,000 = 10,000 ng/mL = 10 ug/mL = 10 ppm.
Note: The established tolerance for aldicarb in mint oils is 75 ppm.