The Holmium liquid filter consists of a solution of Holmium oxide dissolved in perchloric acid. This filter is ideally suited for checking the wavelength accuracy of spectrophotometers in the UV and visible range. It has a spectrum with a variety of characteristic, very well-defined peaks in the range between 240 nm and 650 nm.

This filter is recommended in the Ph. Eur. and in the USP for checking the wavelength accuracy in the range of 240 - 650 nm.

Note:
The Ph. Eur. requires that all measurements are carried out with reference to the same solvents (blank) for the background correction. That means for checking the wavelength accuracy with Holmium in perchloric acid (UV5), the solvent (blank) perchloric acid (UV14) must be used as reference.

Ph. Eur. = European Pharmacopoeia
USP = United States Pharmacopeia