Nickel content of standard patch test materials

The nickel sulfate content in standard patch test materials currently used in the US, Europe and Japan was determined by inductively-coupled plasma atomic emission spectroscopy, a state-of-the-art microanalytical method which allows nickel detection to levels of 7 ppb (microg/l). In 2 materials with a nominal concentration of 5% nickel sulfate hexahydrate in pet., the range (calculated averages of triplicate analyses of 3 different batches) was from 4.72 to 4.87% and 4.97 to 5.39%, respectively. In 1 material with a 2.5% nominal concentration in pet., the values ranged from 2.41 to 2.48%. The range seen in a 5% NiSO4 hexahydrate aq. material was 4.95 to 5.03%. The range for 2.5% NiSO4 anh. in pet. was 2.39 to 2.49%. This data suggest a significant improvement in quality control compared to our previously published data.