GRS-5 PHAT™ GC Capillary Column

Similar to the GRS-1 dimethylpolysiloxane phase, the GRS-5 is offered in very thick films as noted below. In addition to the standard range of column configurations offered with the GRS-5 phase type, a new coating technology developed at GRS allows us to extend the functional range of columns coated with this phase type by the application of very thick films of the GRS-5 phase. For example, films up to 3.5 microns on 0.10mm I.D. fused silica and 18.0 microns on 0.53mm I.D. fused silica are now possible. These PHAT phase™ thick film columns are ideal for low molecular weight analyses previously performed on packed columns.

Advantages of PHAT PHASE™ fused silica capillary columns include:

• greater sample size for trace analyses of very volatile compounds
• increased retention of volatile compounds leading to higher elution temperatures

GC analyses of gases and other types of low molecular weight compounds have been traditionally accomplished on packed columns with heavy loadings or adsorbent type columns. More recently, porous layer open tubular (PLOT) capillary columns have been utilized in the separation of low molecular weight applications despite the drawbacks in using these types of columns such as sample adsorption and bead migration within the column.

Attempts have been made to use ‘thick filmed’ wall coated open tubular (WCOT) capillary columns but the films have typically been confined to a maximum of 8.0 microns due to limitations in conventional column coating technology. While these ‘traditional’ thick film columns have been used for some for low molecular weight applications, they could not attain the separations and sample loadings that could be achieved on packed columns.

By employing our proprietary coating technique we are now able to reproducibly manufacture fused silica capillary columns having phase ratios comparable to heavily loaded packed columns. The PHAT phase™ columns are available with GRS-1, dimethylpolysiloxane and our GRS-5, 5% phenyl methylpolysiloxane phases in lengths up to 30 meters. These PHAT phase™ thick film capillary columns are ideal for low molecular weight analyses previously performed on packed columns.

The two SEM photomicrographs below are of a 0.53mm I.D. fused silica column coated with GRS-1 dimethylpolysiloxane PHAT phase™. Figure 1 (at 142x magnification) clearly shows the internal diameter of the 0.53mm I.D. column and the thick film coated on the internal surface. Note that the phase coating is similar in thickness to the columns’ outer polyimide coating, which is typically 15-20 microns.

Application areas for these PHAT phase™ columns include the analysis of natural gas, auto emissions, light hydrocarbon refinery cuts, amines, alcohols, free fatty acids, refrigerants, residual solvents and air pollutants as defined in the EPA TOC Methods.