Definition of Breakthrough Volume

The term Breakthrough Volume is defined as the volume of Carrier Gas that will purge an analyte through one (1.0) gram of adsorbent resin in a desorption tube at a specific temperature.

In order to better explain this, a Typical Desorption tube is shown below. The desorption tube is normally a tube 2 to 12 inches in length and about 0.25 inches in diameter and is packed with 1.0 gram or less of adsorbent resin. The resin is held in place by two glass wool plugs, one on each end. When analytes are injected onto one end of the resin bed and purged with carrier gas, the analytes will migrate through the adsorbent resin trap. In essence what we really have is a small packed GC column with the adsorbent resin acting like the liquid and stationary phases. As in a GC column the analyte will have a retention time based on resin bed volume, column flow rate and temperature of this small column. The term Breakthrough Volume is actually the retention volume of the analyte, but in order to express this value in meaningful terms that can be used universally with various column sizes it is expressed as the volume of carrier gas that will purge the analyte off a given weight or volume of the resin bed at a specific temperature. The most common units of measure are Liters per Gram of resin, but Milliliters per gram of Resin are also used.

Breakthrough Volume data is important in order to assure that the analytes of interest are not purged off the resin bed during sample collection. This data can also be used to purge off lighter volatiles such as solvent fronts from internal standards injected into the resin bed. One can purge off large volatile peaks such as to remove the ethanol from wine samples in order to better analyze the flavors in the wine. To see an example of the use of this technique hyperlink here.

One must remember that the Breakthrough Volume number is much like a GC peak in a chromatogram. This Breakthrough Volume Peak has some width or resolution associated with it. In other words if the reported breakthrough volume for an analyte is 1.0 Liters per gram, then purging one gram of resin with 1.0 Liter of gas will only remove about half the analyte during the desorption process. In order to remove all the analyte, one should typically double the breakthrough volume number. By purging the one gram of resin with 2.0 Liters of gas, all of the analyte will be removed from the resin bed.

During the collection process, the analyst must be certain that all of the analyte collected remain on the adsorbent trap. To assure that no analyte is lost during the sample collection process (adsorption), the Breakthrough Volume data is typically divided by 2. In the example above where the breakthrough volume is 1.0 Liter per gram, then the sample should not be purged with more than 500 mL of gas. This 500 mL of gas includes the volume of gas sampled during the sample collection phase as well as the subsequent volumes of gas used to purge the resin bed before the sample is analyzed.

In summary breakthrough volume is defined as the calculated volume of carrier gas per gram of adsorbent resin which causes the analyte molecules to migrate from the front of the adsorbent bed to the back of the adsorbent bed. The term Breakthrough Volume has also been referred to as retention volume and also the specific retention volume. The units of breakthrough volume are usually expressed as liters/gram.

A more detailed description of Breakthrough Volumes is in the article entitled: "Calculation and Use of Breakthrough Volume Data." and in Application Note 32.