Amount of nickel applied with a standard patch test

The concentration of nickel sulphate was determined in 9-16 mg test samples from commercially available patch test antigens. With two different manufacturers of 2.5% nickel sulphate in pet, the concentration range of 25 samples was 0.7 and 1.1% (+/- 2 SD) respectively, and with one manufacturer of 5.0% nickel sulphate in pet, the range was +/- 0.5%. In a normal patch test, the volume of patch test material applied with the Finn chamber technique should be 12-18 microliter (9-16 mg), but has been found to range between 9 and 50 microliter. Thus the amount of nickel applied in standard patch tests varies within at least 6-fold limits.