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Using Potassium Bromide (KBr) in UV/VIS spectroscopy

by dhaffnersr | May 05, 2016 09:18 05 May 09:18 | #13077 | #13077

Using UV/VIS spectroscopy, either an unknown substance can be identified or the concentration of a known substance determined. In both cases, accurate analytical results depend on the use of very pure solvents for sample preparation, this is why I used my own variation of a regent called Uvasol.

Potassium bromide (KBr) is transparent from the near UV to long-wave IR wavelengths. It has no significant optical absorption lines in its high transmission region. It has high UV transmittance and low UV absorbance.


To make my KBr preparation, I dissolved 1g of KBr in 250ml of distilled water and vortexed in a magnetic stirrer until no particles remained. The KBr that I used is lab quality (for R&D use only) certified 99+% purity CAS No.: 7758-02-3

You will notice on the calibration curve graphs that, the data points for the KBr are closer to the trend line than the ones for the fluorescein in regular distilled water (pH of 6.5.) This can be significant because it demonstrates a validation of analytical accuracy, at least this is my assumption based on these initial results using this particular regent.

One caveat to keep in mind is, this regent will only work in polar compounds, and it will separate in non-polar substances and render any analysis a moot point. I know this because I have tried it.

Several sub-solvents will work including; ethanol (because it has polar properties as well.) water, Isopropyl alcohol, methanol and acetone. All aforementioned solvents will homogenize very well with the KBr regent. These are just initial results, but look very promising, so logic certainly dictates a move in this direction further.

Another point I want to make is on the graph showing absorption and concentration levels, you will notice all 5 samples hit their mark at 77microlitres. I was very happy with that result because it demonstrated to me that with the equipment I am presently utilizing, it is of sufficient quality to carry out this type of detailed chemical analysis using a homemade spectrometer.




A correction to the KBr preparation; I stated a 1g prep in distilled water, it is 4.0g of KBr in 250ml of distilled water.

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