I need help with the USP Glycerin test for the limit of Diethylene Glycol. I'm running on a Agilent 6890, split with 10:1 ratio. Water based solutions. 0.05mg/ml std concentration. OVI-G43 capillary column, 30m - 0.53mm, 3micron film. Linear velocity flow of 38cm. Problem is that I have a terrible ramp covered with multiple peaks coming off for the last two thirds of the run and my peaks of interest are not showing up. They show at higher concentrations(.5mg/ml) Any ideas about this would be appriciated. Thanks.

Mike, I work for a major U.S. soap company, and we make our own USP grade glycerine, so we (R&D)had to incorporate this new USP test for our production facility. Like some other USP test methods, this one is not well-written, so as usual we re-wrote into our own format. The only thing I could figure out why and when the USP reference glycerine would be needed would be to establish a retention time, and maybe for the resolution solution. Anyway, we worked this out at R&D, and transferred to production QC where it is now used. I'm going try to upload some sample chromatograms in a later posting. We did find it important that the inlet liner be of an inverted cup type (Restek #20990 mini-Lam split liner) or a spiral type (Restek #20706 cyclosplitter). We are able to see peaks of the 0.05 mg/ml DEG.

OK, here's some chromatograms. I don't know if the annotations will show up so first is dilute resolution solution of DEG and glycerine, second is 0.05 mg/ml DEG, and third is actual glycerine sample. The X-axis may be slightly different on these, go by retention times. Post back next week if you're still having problems.

res2.cdf res2.cdf (26 k)

deg.cdf deg.cdf (26 k)

glyc.cdf glyc.cdf (26 k)