I am preparing a solution of 0.02 mmol of compound A in 2ml of acetonitrile or toluene.
The solution of compound A in acetonitrile is then measured by UV-Vis (600 to 190 nm range) using a high quality quartz cuvette.
(A) The machine asks me to introduce the blank, so I introduce the cuvette only with acetonitrile.
(B) The machine asks me to introduce the sample, so I introduce the same cuvette again with acetonitrile to make sure the reading is zero after the blank reading; result = the spectrum shows a flat line with zero absorbance (as expected).
(C)Then I insert the solution of A/acetonitrile ;result = nice curve showing peaks of Abs.
However, when I repeat steps (A) and (B) using the solvent Toluene instead, I always obtain a reading of absorption in step (B). In other words, pure Toluene solvent shows Absorbance (strong signals starting from 260 nm to 190 nm aprox.) when the blank was exactly the same cuvette. Finally, in step (C), I have a mixture of Toluene and Compound A absorption.
Why does it happen with Toluene and no with acetonitrile?
Additional information: The tests were done using two separate UV-Vis machines, yielding the same results. Compound A has to be used with pure Toluene and no with a mixture (e.g., toluene/hexane).
Please look at the following below links which may help you in your analysis:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.628.65&rep=rep1&type=pdf
https://www.philadelphia.edu.jo/academics/ajaber/uploads/CHEM%20540-UV-Vis-%20061-lect%201.pdf
https://ui.adsabs.harvard.edu/abs/2013AGUFM.A23A0165G/abstract
Thanks
Before using any instrument you have to learn basics of chemistry/physics, which are behind the instrument. Read whatever textbook on UV-Vis spectroscopy to find an answer. My answer:" your instrument can't find a black cat in a dark room"
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