What factors contribute to an incorrect CSA ratio for CD calibration?

27 March 2024 1 2K Report

Hello everyone!

I am new to circular dichroism spectrometry, and am running into a problem with our CD spectrometer (Aviv 202). One calibration that is recommended is checking the ratio of the peaks at 192.5 and 290.5 for 1mg/ml CSA in a 0.1cm pathlength cuvette. Previously (many years ago) our machine recorded CD ratio at 192.5nm/290.5nm = 29.6mdeg of 1.97. Currently I am recording a CD ratio of 1.21 (the 290.5nm peak matches the original signal, however the 192.5 is changed).

As I'm reading online, the ratio is expected to be between 1.9 and 2.2.

What could be a source of this error? Lamp alignment issues? Some other calibration needing to occur? Lamp life?

The s/n ratio is acceptable, but a bit worse than the original test.

Thanks!

Danny G.

Rob Keller

Dear Daniel Gitlin Indeed the first thing that crossed my mind is the 'lamp life' You mentioned many years ago so that sounds as a plausibel reason.

Another thing that crossed my mind is the quality of your sample, I read here (in the abstract): Article Two-Point Calibration of Circular Dichrometer with D-10-Camp...

that some purification needs to be performed first.

Best regards.

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