Published by Jack Cochran, VUV Analytics on July 17, 2017

Gas chromatographers have been taught for ages now to pay attention to van Deemter (or at least, his equation) to get the best separations by using an appropriate linear velocity for a given carrier gas.  Unfortunately, “appropriate” can be a synonym for “slow”.  So, if you’re impatient like I am then you may not want to wait for all that efficiency.  Fortunately, I have a handyman’s secret weapon in my lab, a vacuum ultraviolet spectrometer that can do “separation” at the end of the GC column.  That allows me to compress the chromatography for higher throughput analyses, like Lindsey Shear-Laude and I recently did for residual solvents in pharmaceutical products.

Our static headspace – GC-VUV method used a 30m x 0.25mm x 1.40µm Rxi-624Sil MS column with a constant flow of helium at 4 mL/min and a 30°C/min GC oven temperature ramp for combined analysis of Class 1 and Class 2 residual solvents.  The fast carrier gas flow rate and oven temperature program allow quick elution of the compounds of interest (Figure 1) and the GC run time (8 min) matches very well with the headspace incubation time (10 min).  Sure, we had coelutions, but we can deconvolve (i.e., “separate”) them (Figure 2) based on the uniqueness of their absorbance spectra (Figures 3 and 4).
static headspace residual solvents
vacuum ultraviolet absorbance
vacuum ultraviolet absorbance spectrum for benzene

vacuum ultraviolet absorbance spectrum for 1,2-Dichloroethane

If you want more details on this work than I can give in a short blog post, be sure and tune in to Lindsey’s LCGC webinar on July 18, 10 to 11 AM, CDT.  Register at our pharma page by clicking this link:  Analysis of Residual Solvents in Pharmaceutical Excipients and Products with Static Headspace – Gas Chromatography – Vacuum Ultraviolet Absorbance Spectroscopy