Multistandard for the determination of Cadmium, Chloride, Chromium, Iron, Fluoride, Sulphate and Zinc for checking the NANOCOLOR® tests 1-13, 0-14, 0-19, 0-21, 0-24, 1-25, 1-36, 0-37, 0-40, 1-42, 0-86, 1-95 and 0-96