Validating copyrighted instruments


10-Apr-2019 02:07

Stray light is light outside the specified wavelength that shines onto the sample.

For example, when measuring the absorbance using light at 220 nm, accurate measurements are not possible if a lot of light at wavelengths other than 220 nm hit the sample.

The emission lines of a deuterium or low-pressure mercury lamp or the absorption peaks of an optical filter for wavelength calibration are generally used to verify the wavelength accuracy. Consequently, the instrument’s wavelength accuracy can be verified by measuring the energy spectrum of a deuterium lamp, investigating the wavelength of the peak near 656.1 nm, and then comparing its wavelength value to 656.1 nm.

For example, if the detected peak wavelength is 656.2 nm, the error from the true 656.1 nm value is 0.1 nm, and this becomes the wavelength accuracy of the instrument.

Alternatively, a sample with 0.01 % transmittance (4 Abs) appears to have a transmittance of 0.02 % (3.6990 Abs).

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The noise level is defined as the maximum deviation (maximum distance between peak and trough) of the absorbance measured over one minute at a specific wavelength near 0 Abs. As the relative noise increases when the emitted light intensity of the lamp drops off over time, the noise level becomes higher.

Let us consider the case of 0.01 % stray light outside the specified wavelength.