Date: 30-AUGUST-2012 Last Updaed: 8-AUGUST-2026
Understanding the Difference Between Wavelength Accuracy and Absorbance Accuracy
UV-Vis spectrophotometer qualification typically involves several separate performance tests, including:
- Wavelength accuracy
- Absorbance accuracy
- Absorbance linearity
- Absorbance precision
- Stray light evaluation
Each test requires a specific reference material designed for that purpose.
One of the most common misconceptions in UV-Vis qualification is the assumption that a Holmium Oxide standard can be used for all qualification procedures.
This is not correct.
Holmium Oxide Is a Wavelength Accuracy Standard
The Holmium Oxide Calibration Standard (PQA-HOX-01) is intended exclusively for verifying wavelength accuracy.
Holmium Oxide contains highly defined absorbance peaks at certified wavelengths, making it ideal for determining whether a spectrophotometer is measuring wavelengths correctly.
It is commonly used to:
- Verify wavelength accuracy
- Verify wavelength repeatability
- Support UV-Vis instrument qualification programs
- Confirm monochromator performance
Because its absorbance values can vary significantly, Holmium Oxide should not be used as an absorbance accuracy standard.
What Should Be Used for Absorbance Accuracy Qualification?
For absorbance accuracy qualification, the preferred reference material is a certified potassium dichromate solution.
Within the MICROSOLV UV-Vis Qualification Kit, this corresponds to:
Absorbance Solution #3
- Potassium Dichromate
- 0.06000 mg/mL concentration
Potassium dichromate standards are widely accepted for:
- Absorbance accuracy verification
- Absorbance linearity testing
- Instrument performance qualification
- Regulatory compliance programs
This approach is consistent with commonly accepted UV-Vis qualification practices used throughout the United States and internationally.
Why Potassium Dichromate Is Used
Potassium dichromate provides well-characterized absorbance values at multiple wavelengths and concentrations.
These properties make it suitable for evaluating:
- Absolute absorbance accuracy
- Photometric linearity
- Qualification report documentation
- Instrument performance over time
Reference solutions supplied with UV-Vis qualification kits are used together with potassium dichromate standards to perform these evaluations correctly.
Qualification Kit Resources
The MICROSOLV UV-Vis Qualification Kit includes NIST-traceable reference standards used for:
- Wavelength accuracy qualification
- Absorbance accuracy testing
- Absorbance linearity verification
- Precision testing
- Stray light determination
Laboratories performing UV-Vis qualifications should ensure that the appropriate reference material is selected for each performance test rather than attempting to use a single standard for all qualification requirements.