Chromatography Forum

I wanted to see if anyone out there had any experience with the Glycerin Related Compounds method. This is the method that uses water as the diluent. I have been running it for a while now it runs smoothly most of the time. The one thing that I was wondering though was if anyone has seen a large mass appear near the end of an injection(usually around 14-20 minutes). I have seen this occur several times. It has shown up in different vials(ss soln, spl soln, and water) and doesn't seem to have any rhyme or reason to it. It has also shown up on different columns and different GC's. I am using a cup sink liner. It states that a spiral liner could be used as an alternative. Could the liner be causing this? Does anyone have any other explanation for it?

Hello.
You see the glycerol?
1) It is high-boiling liquid. Can be retained on the column for a long time and leave in next injection.
2) Aqueous solutions of glycerol-viscous .better wash the syringe.
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I've run the USP glycerin tests quite a few times from about 2000 to about 2009. This USP monograph has changed more often than my underwear. Although I can understand why USP has moved DEG and EG into the identification part as a way to ensure that there would be no economically motivated adulteration, no one would bother to intentionally add DEG or EG at such low levels as measured there, wouldn't be economically feasible.

USP procedures in the past were from water, then methanol, then water, with and without trichloroethanol internal standard, very confusing. However, in your question, I agree that the large peak is glycerin itself. We did use the liner as stated in the monograph, and we washed the syring with water in this instance. Yes, we did use different inlet liners for the DEG-EG part and the Related Compounds parts.

As an aside, in the late 1990s, I saw a 60 Minutes story of poisonings somewhere through adulterated glycerin. I wrote 60 Minutes (this was before E-mail) and told them I had an easy way to check incoming glycerin for DEG and/or EG adulteration that was straightforward; but I never got a response back.

I have talked with several people from different places about this method. It appears as though the thermal expansion of the water in the inlet is causing this large peak that I am seeing. I am going to try using a spiral liner instead of the cup splitter to see if that helps.

We've used Restek #20706 cyclosplitter with Agilent GC.

What is the origin of the glycerin? Could there be a contaminent in it like a trigliceryde? Or a fatty acid?

I have another issue with the Related Compounds of Glycerin USP. We have an internal requirement of obtaining a standard %RSD of NMT 10.0% and we fail more times than it actually passes. Any ideas what may be causing this? Does anybody perform reproducibility on the standards successfully without any issues? If so, can I get the information on column, liner, etc etc used so I can try to obtain a better reproducibility?

Thanks!