Can one use a mixture of compounds when making a standard solution for UV-Spectrophotometry. For instance, one is attempting to find the casein concentration of milk using UV-spec and they have milk protein which has casein protein in, but not pure casein protein. Would it be feasible to make the standard solutions using the milk protein, knowing how much casein is in it, even if there are other proteins in there or if it is not pure casein?

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    $\begingroup$ In general I would say yes, if you are sure that the absorption spectra do not overlap. Besides, even in that case other interferences might happen, for instance if a coloring reaction must be performed on the "standard" and on the analyte. $\endgroup$ – Alchimista Apr 15 '19 at 13:46
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    $\begingroup$ @Alchimista's caveat that the peaks don't overlap is a big assumption. UV-VIS peaks are very broad. With something as complex as milk there must be numerous compounds that would respond in the UV-VIS range. You'd also have to consider scattering. $\endgroup$ – MaxW Apr 15 '19 at 15:46
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    $\begingroup$ @MaxW. Agree. But this is a problem mostly of the OP sample rather than of my general comment. The latter is anyway meant to circumvent lacking of a pure reference. $\endgroup$ – Alchimista Apr 15 '19 at 17:43
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    $\begingroup$ One problem with spectroscopic techniques for colloids is that there is not only absorption but scattering as well which can confound the results. $\endgroup$ – A.K. Apr 15 '19 at 17:57
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    $\begingroup$ @Alchimista - Sorry my comment above wasn't worded well. I agree with your first comment. I was just trying to point out to the OP that the broad peaks in UV-VIs mean that peak overlap is a common rather than rare occurrence when there are multiple UV-Vis sensitive species. $\endgroup$ – MaxW Apr 15 '19 at 18:13

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