Like its liquid counterpart, the holmium glass filter produces characteristic peaks that make it suitable for use as a wavelength reference material in the UV and visible regions of the spectrum (240 nm – 640 nm). Unlike the liquid cell, however, It is not adopted by all the Pharmacopoeias for wavelength qualification.
It is accepted for this purpose by the following bodies:
United States Pharmacopeia
American Society for Testing and Materials
Therapeutic Goods Administration (Australia)
Description and Discussion
Glass filter containing holmium oxide, mounted stressfree in an anodised aluminium holder. As a solid material the holmium glass filter is physically more robust than the equivalent liquid cell, and can therefore be used in more demanding environments, making it especially useful as a routine wavelength check. Sliding window covers are provided to protect the surface from damage when not in use. Variations from melt to melt of the glass can causesmall uncertainties in peak position, so each Starna filter is individually certified.
The spectrum shows 11 characteristic and well-defined peakscovering the wavelength range from 240 nm to 640 nm.
Approximate peak wavelength values (in nm) are: 242, 279, 288, 334, 361, 419, 446, 454, 460, 537, 638
Note: The above values are for guidance only. Because the absorption bands are asymmetric, measured values will bespectral bandwidth dependent. The Calibration Certificateaccompanying each Starna Holmium Glass Reference givesactual values measured at bandwidths of 0.10, 0.25, 0.50, 1.00, 1.50, 2.00 and 3.00nm, and only these certified values should be used for instrument qualification. On request, Starna can provide certified values at other wavelengths andbandwidth values.
Holmium glass filter