Question on Solvent Purity

[chemist IP]

Hihi

I am currently working on a quick analysis of the purity of solvents in my lab.

I tried to inject the solvents (ie. MeOH, CH3CN, IPA, THF) on a C18 column using water as the mobile phase, hoping to scan for minor impurities that can be present in the solvent. Flowrate was set to 1ml/min.

I used pure water as my mobile phase as it has no absorption in my scanning range. However, my spectrum looks weird for CH3CN n IPA, they have negative absorption. Is that suppose to be the case? As for MeOH, it looks alright =). But for THF, there is a peak coming off on the chromatogram, was thinking that could have been the polymerize thf?

Also, since the solvents dun have chromophores, there will be no peak on the chromatogram and it is not possible to determine peak purity. Is that right??

Sorrie. Qn might sound abit dump but kinda of new to chromatography so just wanna make sure im on the right track. but if im not, any guidance would be nice

[zokitano]

Firstly, I don't think that your LC method will do the job you want it to do.

Secondly, those solvents and their volatile impurities (you didn't mention for what kind of impurities you're after) are conveniently analyzed by gas chromatography.

Regards

[Uwe Neue]

This is not that straightforward. Also, you did not give complete information. It would be good to know the column that you are using as well as the wavelength at which you are monitoring. Some C18 columns do not work well in water (dewetting, see other posts). You will need to work at low wavelength to see impurities.

The more standard approach to examine solvent purity is a practical approach: equilibrate the column with about 5% organic solvent, then run a gradient to 100% organic solvent. If you get peaks, you have junk in your solvents or in your system. The reason for such an approach is that your solvents may very well contain things like plasticizers from containers (screw caps on solvent bottles) that you will not see with your test, but that will be bothersome in real chromatograms.

[chemist IP]

This is not that straightforward. Also, you did not give complete information. It would be good to know the column that you are using as well as the wavelength at which you are monitoring. Some C18 columns do not work well in water (dewetting, see other posts). You will need to work at low wavelength to see impurities.

Hi Uwe Neue, Im actually working with Zorbax C18 column and yes..im working at low wavelengths...doing my scans starting from 190nm. Also, Im monitoring absorption at 210, 254. The more commonly used wavelength.

I spoke to my colleague and he suggested that I use the solvent samples as my mobile phase and inject the water in as sample. Didnt get a chance to run it today. Will probably try out both methods tml and hopefully share some good news....and Uwe Neue....thanks for the suggestion n yes...I thought it was a simple run to do also....when i went into more details...it doesnt look simple anymore but i felt its also kinda of my ignorance n inexperience...still got a long to go i guess