The influence of temperature on the concentration homogeneity of patch test materials

The concentration homogeneity of nickel sulphate 4.8% pet. and potassium dichromate 0.5% pet. in patch test materials appeared to become less homogeneous if stored at room temperature compared storage at 4 degrees C, after 2 months. The coefficient of variation of concentration for nickel sulphate after storage at 4 degrees C was 3.0883%, and at room temperature 25.3098%. The coefficient of variation for potassium dichromate after storage at 4 degrees C was 4.6324% and at room temperature 9.6334%. This indicates that patch test materials containing nickel sulphate and potassium dichromate should be kept refrigerated in the tropics.