Heterochromatic stray light in UV absorption spectrometry: a new test method

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Optical Metrology

Background:

• Accurate stray light measurement is crucial for UV spectrophotometer performance.
• Existing methods, like ASTM Test Method E387, can be complex and require frequent instrument adjustments.

Purpose of the Study:

• To introduce a new, simplified method for quantifying heterochromatic stray light in UV spectrophotometers.
• To compare the efficacy and ease of use of the new method against the established ASTM standard.

Main Methods:

• The new method utilizes sharp UV absorption edge solution filters.
• It involves measuring the apparent absorbance of a 10-mm cell in the sample beam against a 5-mm cell in the reference beam.
• Apparent absorbance maxima recorded during wavelength scans directly indicate stray light levels.

Main Results:

• The new method demonstrated satisfactory agreement with the ASTM E387 method across various spectrophotometers and wavelengths (200-390 nm).
• Tests used solution filters including KC1, KI, NaI, acetone, and NaNO2.
• The new method's absorbance maxima occurred at lower scale values, reducing the need for reference beam attenuation.

Conclusions:

• The developed method provides a simpler and more efficient way to estimate stray light in UV spectrophotometers.
• Its reduced requirement for attenuation makes it more practical for routine use.
• This technique offers a valuable alternative for ensuring spectrophotometer accuracy.