Reason for "why to take baseline?" is, by taking baseline of samples, it cancels the noise effect due to air and inside liquid sample.
Next "how to take baseline".. There are 2 ways..
If the spectrometer is having 2 holders, then place your reference sample in both holders and run the unit.. Baseline correction is done.. Now place the sample and again run the unit..
If the spectrometer is having 1 holder, then place ur reference sample, run the unit.. And then place the sample and again run the unit..
Reason for "why to take baseline?" is, by taking baseline of samples, it cancels the noise effect due to air and inside liquid sample.
Next "how to take baseline".. There are 2 ways..
If the spectrometer is having 2 holders, then place your reference sample in both holders and run the unit.. Baseline correction is done.. Now place the sample and again run the unit..
If the spectrometer is having 1 holder, then place ur reference sample, run the unit.. And then place the sample and again run the unit..
For solution sample, we get lot of peaks/absorption from the solvent as noise. to remove these baseline correction is must. Moreover, even if we do powder sample, we expect some noise.absorption/reflection from the solid sample holder. So to remove all these, we need to do base line correction. The correction is as follows: take your solvent in a cuvette and solution in another cuvette. do the measurement. It will automatically correct the baseline. otherwise first put the solvent cuvette in a single holder system, make baseline measurement and then measure your sample.
Some spectrophotometers have provision for and are programmed to instruct the user to place in a reference sample for baseline measurements. e.g. run 100% and then 0% baseline correction for each measurement mode, say T or R.
I would recommend a blank baseline without anything in, so other users can use the same baseline. If double beam, you can measure the solvent in the reference sample holder and the sample in the other sample holder or measure both in the sample holder and subtract the solvent afterwards. The same is applicable for a single beam.
Baseline is used to subtract the effect of environment, which is not related with the sample itself. To be a scientific report the results should be repeatable in the other labs. eg. the air absorption might be different due to the humidity, temperature, pressure, etc; or some were measured under vacuum or liquid. To extract the real absorption or transmission of your sample, you have to avoid the effect of environment, and even the substrate or base solvent.
Mostly, the equipment can measure either at the condition without sample or with only the substrate (film sample)/base solvent (solution) as reference to beset the transmittance as 100% and absorption as 0; when you insert your sample, the signal will be purely about your sample.
Wonderful answer, Pramodini S . This really helped me to use our new VWR UV6300PC Photometer at the Physical Chemistry Laboratory from the School of Chemical Engineering at the Faculty of Engineering, University of San Carlos, Guatemala. We just acquired this equipment and it has two holders, different to the one we had in the past (1 holder). Thank you very much.
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