In spectrophotometer quality assurance checks, holmium oxide glass filter is used to assess which parameter?

• A. Linearity
• B. Stray light
• C. Absorbance accuracy
• D. Wavelength accuracy

Answer: (D)

Wavelength accuracy.

Holmium oxide glass filter provides a set of sharp, well-established absorption bands at known wavelengths. When you place it in the spectrophotometer and scan, the instrument should show absorption peaks at those precise wavelengths. If the measured peak positions line up with the known values, the wavelength axis and monochromator calibration are accurate. This makes the filter a reliable check specifically for how precisely the instrument can determine wavelength.

This isn’t about how the instrument responds to different concentrations (linearity), nor about how much stray light leaks through when light should be blocked, nor about how close absorbance readings are to true values for a standard solution. The unique, reproducible, narrow spectral features of holmium oxide make it ideal for validating wavelength accuracy.