[Bidagdha_TADIR]

I've read about three methods to check for stray light of uv-vis spectrophotometers - Potassium chloride solution (1.2% w/v) measured at 198nm, Sodium iodide solution (1%) measured at 220nm and Sodium nitrite solution (5%) measured at 340nm.

But is there any way to measure stray light with Visible range in mind?

Secondly, since most instruments have a range of 200-800nm, what is the point of measuring Stray light at and below 198nm? And how would a instrument that runs at 200nm-800nm measure absorbance at 198nm? It is said that KCl test is the most important of three.

[Arkcon]

What does the stray light test do?  How does it work?  Once you know that, you can adapt it to any wavelength. 

Why does it matter though?  You're looking to determine light leaking around the sample holder, or in another way leaking into the optical system.  Is that wavelength dependent?

[Bidagdha_TADIR]

I think wavelength does have impact. For example, the Sodium iodide solution absorbs all radiation at and below 220nm completely (0% transmission), so if any absorbance is shown by the instrument at and below 220nm, it is due to stray light.

What I read is that, stray light originates because the monochromator, in addition to producing the analytical wavelength, also produces small amount of other wavelengths due to imperfection of the optical surfaces, and these other wavelengths are detected by the detector. So for different analytical wavelength, the amount of stray light may be different.

The Thermoscientific Technical note had this to say -

It is important to remember that instrumental stray light is a function of the “sample”, which includes the cell, the solvent, and the solute. Thus, a stray light measurement with a cut-off filter does not necessarily guarantee that the same level of stray light will be present when a sample is in the beam. However, the cut-off filters are excellent for determining the performance of the spectrophotometer and monitoring instrument performance over time.

So basically, the intention of this test isn't to determine the amount of stray light, rather it checks how good the monochromator is at not producing stray light. But the test is only checking this performance attribute at UV region, not the Visible region. That's why I need to know, if there is any test to check this performance at visible range.