PEG (aka Wax) phases for my GC/MS -- Why Not?

As I sit here in Technical Service I have another call on Wax phases and it’s a common question: “Why shouldn’t I use my PEG (polyethylene glycol) phase for GC/MS, especially since I am using relatively low column temperatures.” While my rehearsed answer is partially correct (“because they bleed too much”), it does not answer the question. The answer has more to do with the PEG bleed mass spectrum than the bleed intensity. PDMS (polydimethylsiloxane) based polymers show a few high EI m/z ions (e.g. 207, 281, 355...), whereas a PEG spectrum is made up of hundreds of ions that raise the MS background for essentially the whole acquisition range. If we think about the bond energies of PEG versus PDMS it makes sense that 70eV is going to scatter PEG into many more ions than the stable cyclics that make up PDMS bleed, which leads to an overall loss in sensitivity. For those that require the selectivity of a PEG phase by MS make sure you lower your source temperature and strictly observe the max temperature of the column.

Further reading: Want to check out our Stabilwax columns?