Storage: Store in an airtight container, protected from light, A white or almost white powder; very hygroscopic. It shows polymorphism, The principal spot in the chromatogram obtained with the test solution should be similar, in position, colour in daylight, fluorescence in UV light at 365 nm and size to the principal spot in the chromatogram obtained with reference solution (a).The test should not valid unless the chromatogram obtained with reference solution (b) should show two spots which may, however, not be completely separated.