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How to make sure your new GC capillary column will fit into your GC oven

16 January 2023
  • Alan Sensue
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I recently spoke to a customer who said she was having a difficult time finding the catalog number of the column she was trying to order. I asked for the catalog number, and she provided 70112-6850. I instantly knew what the problem was, she paired a MXT column catalog number (70112) with a fused-silica column suffix number (-6850). I began to wonder how many of our other customers experience the same confusion. As a result, I decided to write this post to help clarify this topic.

As you may know, especially if you have a GC without a “full size” oven, not all GC capillary columns will fit into your GC oven. For example, several of the most common requests we receive are for columns which fit into the oven of most SRI GC’s (and Buck Scientific) and an Agilent 6850 GC oven. In addition, with the increase in number of compact mobile GC's, smaller OD (outside diameter) columns are more popular than ever. 

Fused-Silica capillary columns

So what do you need to know when purchasing a new capillary column for your instrument? Let's start with fused-silica columns. The majority of our fused-silica columns listed in the catalog and on the website (five-digit catalog numbers which begin with a “1” or "4") are wound onto cages (which we call the 11-Pin cage) which are approximately 7.25-inches outside diameter (and approximately 1.5-inches wide).

FS2 Column

11-Pin Cage

If you need a smaller cage, we also offer a 5-inch OD cage (and approximately 3-inches wide). To obtain a column on this smaller OD cage, simply take the fused-silica column five-digit catalog number and add a -6850 suffix to this number. (please note that 105-meter columns which have an internal diameter of 0.53mm are not available on a -6850 cage).   For those of you who may not be familiar with Agilent GCs, the 6850 model has a slightly smaller oven than many other Agilent models and therefore needs a smaller cage.


Cage (with string)

For example, the catalog number of a Rxi-1ms, 30m x 0,32mmID x 4µmdf column wound onto a 7.25-inch OD cage is 13396. To have this column wound onto a 5-inch OD cage, add the suffix -6850, so the new catalog number becomes 13396-6850. Please note that many of the -6850 columns are not listed on the website. If you do not see the catalog number you need on the website, contact customer service. 

MXT (Metal) capillary columns

Our metal MXT columns are the most popular choice for capillary columns which need coiled (wound) to outside diameters (OD) less than 5-inches. Unlike fused-silica tubing that can become stressed the smaller you wind it, metal tubing does not have this problem (within limits). However, once the metal tubing has been wound (coiled), do not try and coil it to a different diameter because kinks in the tubing may result.

There are three popular sizes (OD) with MXT columns. The product web pages for MXT columns normally list the OD for that particular part number, so be sure to take a look before ordering.

The first is similar to fused-silica capillary columns; 7.25-inch OD (11-pin cage). These columns include our MXT-PLOT (Porous-Layer-Open-Tubular), our MXT-Biodiesel TG, and our MXT-1HT SimDist columns (Simulated Distillation).

11-Pin Cage

.The second popular size (OD) is what we refer to our standard size column which is not actually wound onto a cage, but the coiled column layers are what is referred to in our literature as “Banded” (I call it bracketed). Depending upon the column's length, these columns may range from an approximate OD of 4.5-inches to 5.5-inches.  MXT columns with 0.28mmID and 0.53mmID tubing resemble the photo below (labeled Standard MXT Cage).  Other sizes resemble "Bundled" (shown in the last photo and described in the next paragraph).  Those columns which are "Bundled" include MXT columns with internal diameters of 0.32mm, 0.25mm, 0.18mm, and those with the -273 suffix (and similar suffixes).  See last photo for example.

 Standard MXT Cage.

One of the most popular sizes of MXT columns is our 3.5-inch OD, which is the choice for most SRI (and Buck Scientific) and mobile GC's. Like our “standard” MXT columns, these columns are not wound onto a cage, but unlike the standard columns, these columns simply have a few metal bands which keeps the coils together and are not in layers. This is referred to in our literature as “Bundled” (see photo below comparing a 0.25mmID fused-silica column to a 0.25mmID MXT column). To obtain a column with this smaller OD, simply take the MXT column five-digit catalog number (the five-digit MXT column number will begin with a “7”) and add a -273 or a -2731 or a -2732 suffix to this number.  The difference between the -273 and -2731 and -2732 is as follows; the "leads" or length of tubing ends (front & back) that are not "Bundled" with the rest of the column are either approximately 36-inches for the -273 suffix columns, approximately 18-inches for the -2731 suffix columns and approximately 9-inches for the -2732 suffix.  SRI (and customers who own their GCs like the 8610C) seem to prefer the -2731 and -2732 suffixes (with the shorter 18-inch and 9-inch leads).  Columns with the -273 suffix (with the longer 36-inch leads) seem more popular with certain process GCs.


For example, 70112 is a 5-meter x 0.53mmID x 0.1µmdf MXT-1HT SimDist columns. To obtain this column with a 3.5-inch outside diameter (no column cage), the catalog number you will want to order is 70112-273 or 70112-2731.


Finally, remember in my introduction paragraph I mentioned that MXT columns with the -6850 suffix do not exist?  There is a -6850M suffix for MXT columns.  However, there is not a special cage for this suffix number.  Instead, these MXT columns are coiled to a 5-inch internal diameter (approximately 5.25 inches outside diameter) and banded with copper wire.

If you are wondering about packed columns while reading this, none of these suffixes will work; packed columns have their own list of suffixes.  Please review Things to Consider Before Ordering a Packed Column 

Thank you.

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