[Compass]

Hello,
First time posting, hope I'm in the right spot. I work at a chemical plant and I'm trying to analyze some cleanouts for product. The cleanout is in acetone and I'm attempting to just use UV/vis to find the wave length this product reads at. I'm using a Cary 50 UV spectrometer. My problem is when I go to do a full spectrum scan everything from 199nm to 300nm is just noise. Lots of very sharp peaks. I thought I had too strong a solution but diluting it down did nothing. Then I realized that it's the acetone causing this. I baseline with neat acetone, then read that acetone it gives me the same noise and not a flat baseline. Is pure acetone an issue? As a side not, I'm not a chemist, just a lab tech with minimal chemistry knowledge.

Thanks in advance for any help.

[Corribus]

Acetone or any solvent with a carbonyl will have an absorption in the UV, I think about 260 nm or so. The UV cutoff is about 325 nm. (That means you shouldn't use it at wavelengths below 325 nm as a solvent in UV/Vis).

So to directly answer your question: Yes, acetone is your issue. If you need to scan below 300 nm, try a different solvent with a lower UV cutoff. You can find tables around the internet. Or just ignore it if you don't care about that region.

[wildfyr]

I would suggest you evaporate off the acetone on your analytes, then use pure methanol or acetonitrile to run UV-Vis if you care about things below 320 nm or so.

[Compass]

Thank you very much. This answers my issue. Evaporating the acetone off is a very clever trick, I like it. My manager was hoping for something quick and dirty and I don't think that's going to happen this way. I think now my best route is HPLC.

[Babcock_Hall]

I suspect that others here have as much or more direct experience as I do.  However, I would like to point out that solvents may contain impurities.  Therefore when performing spectrophotometry I will generally use spectrophotometric-grade or HPLC-grade commercial solvents.

[DrCMS]

You are all missing the point of this analysis; in the factory that Compass works at they have cleaned a reactor with acetone (industrial grade) and Compass has been tasked with working out how much product is in the acetone.   They have already done this so they are not going to switch solvents, it is about how well it cleans the reactor and cost not it's UV absorbance that acetone was chosen for.  They are not going to clean reactors with HPLC or spectrophotometric grade solvents due to the massive cost of those.   

Unless the product has an absorption in the 350-700nm range then UV/vis is not the ideal technique for this.  Do you have a GC available?  Alternatively get a sample of the virgin acetone (in case it already has impurities in it) and a sample of the cleaning acetone and evaporate them to dryness and compare the residue weights. 

[Compass]

You are all missing the point of this analysis; in the factory that Compass works at they have cleaned a reactor with acetone (industrial grade) and Compass has been tasked with working out how much product is in the acetone.   They have already done this so they are not going to switch solvents, it is about how well it cleans the reactor and cost not it's UV absorbance that acetone was chosen for.  They are not going to clean reactors with HPLC or spectrophotometric grade solvents due to the massive cost of those.   

Unless the product has an absorption in the 350-700nm range then UV/vis is not the ideal technique for this.  Do you have a GC available?  Alternatively get a sample of the virgin acetone (in case it already has impurities in it) and a sample of the cleaning acetone and evaporate them to dryness and compare the residue weights.

You are correct, I have to use the plant acetone. I do have a GC I'm working on setting up to analyze this. The product I'm cleaning out I don't think has ever been analyzed on a GC so we'll see how that goes. I'm playing around with my HPLC (the product is normally run that way) but the issue I'm facing with that (which would be the same for evaporating the acetone and weighing the difference) is that it needs to be below 10 PPM. Unless I can tweak it, the HPLC isn't detecting it at such low levels and I would need quite a bit to evaporate off and get an accurate reading.