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Restek Tech Tip

Commonly Asked GC Questions

Answered by the Restek Chromatography Information Services Group

How do I know which guard column would be best for my application?

Restek offers guard columns and transfer lines ranging from 0.025mm ID to 0.53mm ID, from 1 to 10 meters long, in fused silica or Silcosteel® treated stainless steel. Guard columns are available with nonpolar, intermediate polarity, or polar deactivation, and with several specialty deactivations.

  • In most applications in which nonpolar to moderately polar solvents are used, we recommend an intermediate-polarity (IP) deactivated guard column.
  • For most polar solvents except water, we generally suggest a polar deactivated guard column.
  • For water-based samples, we recommend our water-resistant Hydroguard™ guard columns. This deactivation is designed to withstand the harsh “steam-cleaning” that occurs when water is rapidly vaporized in the column.
  • For applications that require a highly inert surface to minimize analyte breakdown, such as pesticides analysis, we recommend a Siltek® deactivated guard column.
  • For amines or other basic compounds, we offer base-deactivated guard columns.

Also, note that for many of our popular stationary phases, we offer Integra-Guard™ columns — an analytical column with an integral guard column. This eliminates the connection between the guard column and the analytical column.

What are all those different capillary column temperatures listed in your catalog?

The first temperature listed is the minimum operating temperature for the column. The two temperatures separated by a slash symbol ( / ) are the maximum isothermal operating temperature and the maximum temperature program temperature, respectively. The maximum temperature program temperature is the maximum temperature to which the column may be exposed briefly without causing damage. For most stationary phases, the maximum temperature program temperature is approximately 20°C above the maximum isothermal temperature. In addition to these temperatures, the polymer stability temperature sometimes is listed. This is the maximum temperature to which the polymer phase can be exposed before degradation.

I see ghost peaks when I inject a sample or standard, and my mass spectrometer identifies these peaks as a siloxane material. Is there a problem with my column?

Capillary columns can produce a varying amount of baseline noise (siloxane bleed), usually containing fragment ions at m/z 73, 207, and 281, but they will not produce any distinct peaks in an analytical run. The most common sources of distinct siloxane peaks are septum bleed and the chemicals used to deactivate the injection port liner and the glass wool packing material.

Sometimes I experience problems when using a 1701-type column for my pesticides analysis. Are there other column choices?

On-column breakdown of chlorinated pesticides, such as endrin, methoxychlor, and DDT, are common with cyano-containing phases, such as 1701-type phases. Fortunately, there are other column choices. These include a few standard phases, such as our Rtx®-35, Rtx®-35MS, and Rtx®-50 phases. In addition, Restek has developed several specialized columns for pesticides, including Rtx®-CLPesticides & Rtx®-CLPesticides2, and Stx®-CLPesticides & Stx®-CLPesticides2 columns. These columns eliminate on-column breakdown problems, improve separation, and reduce analysis time. Information about these columns, and example chromatography, can be found on our website: www.restek.com

Can I order a fused silica column in a column cage to fit my small GC oven?

Yes. We offer several special cage options for non-standard and portable GC ovens. Please contact our chromatography informations services group at 800-356-1688, ext. 4, for specifics, or customer service (ext. 3) for prices. Please note that we cannot cage or recage columns from other manufacturers.



From left to right: Al Carusone, Tom Bloom, Jonathan "Munch" Keim, Tim Herring, Al Sensue, and Terry Reid