Frequently Asked Questions: Capillary GC Columns
- What can I use to rinse my column?
- Why are amines tailing on my column?
- Which end of my Integra-Guard® column is the guard column end?
- I see ghost peaks when I inject a sample or standard, and my mass spectrometer identifies these peaks as some form of siloxane material. Is there a problem with my column?
- Can I inject water onto my column? Will it damage the column?
- Can I inject acids or bases onto my polysiloxane column? Will they damage the column?
- What are all those different temperatures listed in your catalog for each column?
- How do I condition my GC column?
- Can I order a capillary column in a column cage to fit my small GC oven?
- What types of guard columns do you offer, and how are they deactivated?
- Are fused silica (FS) capillary columns superior to MXT® stainless steel columns? If so, why?
- How do I know which GC guard column would be best for my application?
- What column do I need for the analysis of my sample?
If your question doesn’t appear on the list, you can contact Restek’s expert chemists. (Please remember to include your company name and complete mailing address. Thanks!)
What can I use to rinse my column?
Why are amines tailing on my column?
Which end of my Integra-Guard® column is the guard column end?
I see ghost peaks when I inject a sample or standard, and my mass spectrometer identifies these peaks as some form of siloxane material. Is there a problem with my column?
Can I inject water onto my column? Will it damage the column?
Poor chromatography and/or response for amines often are the result of contact between acidic silanol groups (acidic active sites) and the amines (basic compounds). This interaction can take place within the injection port or in the column. The most efficient way to counteract this negative effect is to use a base-deactivated injection port liner and a base-deactivated column. Restek offers base-deactivated liners and base-deactivated columns in three polarities: Rtx®-Volatile Amine and Rtx®-5 Amine columns are low-polarity, Rtx®-35 Amine columns are moderately polar, and Stabilwax®-DB columns are highly polar. All are designed to reduce tailing of basic compounds.
There are two ways to identify the guard column: 1) it is on the same side as the column tag, and 2) it may be tied separately, with knotted high temperature string.
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.
Injecting small amounts of water (solvent) into a non-polar capillary column will not damage the phase; however, this may not be the case for mid and high-polarity columns.
Several precautions should be taken when water is used as a solvent:
- The water is completely vaporized before it enters the column and the water does not re-condense inside the capillary column. If GC oven temperatures are cool enough to allow the water vapor to condense:
- Use a Polar-Deactivated guard column. This will allow the water to be completely vaporized before it reaches the column.
- Do not use cold or heated on-column injection modes. Use only injection modes that vaporize the solvent before it enters the column: split, splitless, or direct injections.
- The injection volume should be small: 1µL or less. Larger volumes will create a backflash, where the expansion volume of the solvent will exceed the volume of the injection port liner. This can lead to poor reproducibility and/or "ghost" peaks.
Additional information can be found in our Capillary Column Installation Guide
Can I inject acids or bases onto my polysiloxane column? Will they damage the column?
Samples or standards within a pH range of 5 < sample < 9 should not damage a capillary column. Repeated injections of samples with a pH between 4 and 5, or between 9 and 10, might cause column damage. Samples with a pH < 4 or > 10 should be diluted or neutralized before injection, as they will damage a column.
What are all those different temperatures listed in your catalog for each column?
All Restek columns have published minimum and maximum operating temperatures that establish the working range for the stationary phase. Note that these ranges vary with the thickness of the coating.
How do I condition my GC column?
See our article, How to Condition a New Capillary GC Column.
Can I order a capillary column in a column cage to fit my small GC oven?
Yes. We offer several special small cage options for non-standard and portable GC ovens. Please contact our customer service department at (800)356-1688, ext. 3, to order these special configurations.
- To order a Restek column in a 5-inch cage for an Agilent 6850 instrument, add the suffix -6850 to the catalog number for the column.
- To order an MXT® column with a 3 1/2" OD, add the suffix -273 to the catalog number of the column.
What types of guard columns do you offer, and how are they deactivated?
Restek offers fused silica guard columns and transfer lines ranging from 0.025mm ID to 0.53mm ID, from 1 to 10 meters long. Fused silica guard columns are available with intermediate polarity or polar deactivation, and with several specialty deactivations, including base deactivation, Hydroguard® deactivation, and Siltek® treatment. Passivated stainless steel (MXT®) guard columns are also available in 0.28mm ID or 0.53mm ID, with intermediate polarity or Hydroguard® deactivation for our MXT® columns.
Are fused silica (FS) capillary columns superior to MXT® stainless steel columns? If so, why?
Because fused silica tubing has a smoother interior surface than stainless steel, fused silica columns might offer slightly higher efficiencies for phase films of less than approximately 1 micron. For film thicknesses greater than 1 micron, there will be very little difference in efficiency between fused silica columns and MXT® columns.
How do I know which GC guard column would be best for my application?
- In most applications in which nonpolar to moderately polar solvents are used; we recommend an intermediate-polarity (IP) deactivated guard column (available in fused silica or MXT®).
- For most polar solvents, we generally suggest a polar deactivated guard column.
- For applications that require a highly inert surface to minimize analyte breakdown, such as pesticides analysis, we recommend Rxi® guard columns.
- For amines or other basic compounds, we offer base-deactivated guard columns.
- For several of our common stationary phases, we offer Integra-Guard® columns: analytical columns with integral guard columns that eliminate the mechanical connection between the guard column and the analytical column.
What column do I need for the analysis of my sample?
Restek offers a wide variety of capillary, packed, and HPLC columns. There are several good ways to select the most appropriate column for a particular analysis. First, search for applications containing the target compounds. Another excellent resource is our current general catalog, which contains hundreds of applications. Finally, call Restek’s technical support team at (800)356-1688, ext. 4, or contact your Restek representative to discuss the analysis. Our dedicated team will be happy to suggest a column and conditions.