I am going to analyze the degradation of diclofenac carried out by an experimental reactor with UV-VIS spectrophotometry. However I am not sure what concentration I should use to observe changes in absorbance.
What problems could I have to observe the evolution of the absorbance if I use a concentration of the order of mg/L or μg/L?
Thank you for your time.
I think spectrophotometer is sensitive to concentrations in ug/l. However, you can see these articles may help you to choose the best range for concentration of diclofenac.
Article Second Derivative Spectrophotometric Determination of the De...
https://www.scirp.org/html/1-9401363_7516.htm
https://www.deswater.com/DWT_articles/vol_61_papers/61_2017_293.pdf
Also this discussion:
https://www.researchgate.net/post/How_can_we_increase_the_sensitivity_of_spectrophotometric_analysis_methods
You can calculate this from the formula Abs = ext.coeff x conc. x path length. I found a published ext. coeff. value of 13 340 M-1 cm-1 (274nm). You'll have to decide what is a reasonable change in absorbance of course. Let says you start at A =0.5, then concentration required for that absorbance = 0.5/13340 molar, assuming your path length is 1cm.
From my hands-on experience, you would need to establish a calibration curve that is typically valid from 0.00025 to 0.0012 meg/ml, always subject to validation depending on the functional group to be detected and MW of the molecule. Anyway, UV/Vis is more effective than NMR at super low concentrations. In addition, you need to find an appropriate solvent that can boost up but not interfere with signals.
make sure that you use high sensitive spectrophotometer with two path lenght and that make a scan of your sample. beside you should yourself the maximum wavelenght of diclofenac don't use the one of litetraure.
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