Stationary Phase Chemistries: 624-Type GC Phase

Introduction

Often the star of methods analyzing volatile organic compounds, the 624-type gas chromatography (GC) stationary phase is a versatile, low-to-mid polarity polymer that provides at least three different potential modes of interaction with your sample (shown below).

As is common in the world of GC stationary phases, the name doesn’t give much away unless you are already in the know. The 624 phase gets its name originally from US EPA Method 624, “Purgeables by GC/MS,” promulgated in the mid 1980’s. And relatively thick-film formats remain commonly used today for the analysis of a wide variety volatile compounds in a variety of matrices across many different markets.

Different Phases, Same Name

You may encounter variations on the phase structure from vendor to vendor. In some cases, the phenyl content is incorporated into the polymer’s siloxane backbone. In others you may see a phenyl-silicon-methyl group and a distinct cyanopropyl-silicon-methyl group. There will be small selectivity differences based on these variations, but they can all be considered 624-type columns.

Different Names, Same Phase

And yes, the potential for confusion doesn’t stop with the slight differences in the chemistry of the 624-type column. You can find the same phase under different names, so it’s good to recognize the 624 in its various guises!

Adoption of the phase as an excellent choice for the analysis of volatile compounds in pharmaceutical applications meant that the 624 would get its own USP designation, in this case "USP G43."

And the origin of the name “1301-type” is even more obscure. This nomenclature is relative to another GC phase, the 1701-type, which is a 14% cyanopropyl phenyl phase. The 1701-type is named after what you might think it’s named after, if you happen to be a Star Trek fan (believe it or not!). For anyone new to chromatography, though, it’s possible these naming conventions would seem…highly illogical.

Example Applications: