Technical Tips

Should you use a ZB-WAX or ZB-WAXplus?

A Technical Tip by Kory Kelly
GC Product Manager

The ZB-WAX and ZB-WAXplus columns are both PolyEthyleneGlycol (PEG) based phases, but there are two main differences between the two columns. The length of the PEG polymer between the two columns is different and the ZB-WAXplus had undergone an extra processing step to make it resistant to water injections.

The ZB-WAX column phase is comprised of a higher molecular weight polymer than the ZBWAXplus.

The higher weight polymer gives the ZB-WAX has a higher minimum temperature and produces lower bleed at the maximum temperature. At temperatures below the minimum temperature, compounds may still separate but may not show optimum efficiency because of decreased transfer into and out of a more solid-like stationary phase. The minimum temperature limit of the ZB-WAX is 40 °C where the minimum limit of the ZB-WAXplus is 20 °C meaning that the ZB-WAXplus would be more suitable for low temperature volatiles analysis. However, the lower bleed at high temperatures makes the ZB-WAX more suitable for higher temperature analyses.

The second difference is that the ZB-WAXplus polymer has also been stabilized for water injections. Multiple or routine water injections will not alter the efficiency nor polarity of the phase over time. To prevent any problems that may be associated with buildup of compounds, it is still recommended to routinely remove buildup by eluting the water or contaminant.

If either column does become contaminated, the steps to rejuvenate the column’s performance would be similar and are detailed in the column care guide. Trimming the front of the column and conditioning at high temperatures are routine. The ZB-WAX would be more resistant to contamination because it can be exposed to high temperature and exhibit less bleed so it can be conditioned longer with less damage to the phase. Both phases have been bonded so they can also be solvent rinsed, but ZB-WAX should not be solvent rinsed with methanol or water. In many other aspects, both columns are similar. Both columns will be susceptible to oxygen and solvents of extreme pH and therefore these conditions should be avoided on both columns. We recommend the use of oxygen traps for the carrier gas, especially if using the columns near the maximum temperatures.

Both columns are PEG based phase which contain alcohol functional groups that can easily be derivatized with many different reagents. All PEG polymers may be susceptible to some derivatization reagents. Therefore, use caution with derivatization reagents and PEG polymers to ensure that the phase does not become derivatized.

Steps that can be used to extend column lifetime would be to use a guard column to capture nonvolatile materials before they contaminate the column. However, be careful to check connections for leaks which may introduce oxygen. Using a liner with wool will also act as a physical barrier to capture non-volatile compounds. Also avoid samples that are at extreme pHs. In summary, the ZB-WAXplus is best recommended for volatiles applications or samples that may include water. The ZB-WAX would be the preferred column for higher temperature analyses requiring a more polar column.

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