Hello, while working with spectrophotometer, it shows negative absorbance and readings appearing on screen keeps on decreasing,, I a m not getting a static reading. Even if I take the reading of particular sample twice, I get two different readings with huge difference.
Suggest please how to fix this issue?
Negative readings will appear according to the samples that you are subjecting to measure.
As an example,
- the samples with high turbidity values will obviously give negative readings due to the sedimentation of Total Suspended Solids.
There can be various reasons, My example is just a common simple reason.
However, you better calibrate the instrument using reference samples.
Best regards
Make sure that you have light passing through the cell compartment. If so then put water into both cells (if double beam) or the one cell (if single beam) and monition the readings. What happens?
Are you using quartz cuvets or not? Negative absorbance has no physical meaning.
In my opinion, there are two possible reasons for negative absorbance:
1. You have a problem with instrument calibration, which means that your reference sample for baseline correction is contaminated (moisture or other surface impurities). In this case, I would suggest obtaining or creating a clean fresh reference sample.
2. Your sample shows luminescence triggered through excitation of specific wavelength giving higher total light output. You have to note that though the source in the UV-VIS spectrophotometer is monochromatic, the detectors are not, they register net total light output from your sample (whole spectra produced by the interaction of the source beam with the sample).
These are just some reasons I can think of that may cause the negative readings. I am sure there are more.
Clean the cuvettes you are using.. Put the empty cuvettes in spectrophotometer and correct baseline for full wavelength range..
This may happen if you are taking mixture of solvents as blank..
Cuvette cleaning or using new quartz cuvettes is the only possible option..
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