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Determination of Breakthrough Volume

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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. The 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.

In order to determine the Breakthrough Volumes for a large number of organic chemicals the following system was constructed using an Varian GC with an FID detector as the base system.

Figure 1 - GC Oven for Determination of Breakthrough Volumes

GLT desorption tubes, 1/4 in. O.D. x 4.0 mm I.D. x 100 mm long were packed with 250 mg of each of the adsorbent resins between two glass wool plugs. The packed tube was attached between the injection port and the detector of a gas chromatograph (Figure # 1) using 1/16 inch O.D. stainless steel tubing and the appropriate fittings to mate to the GC. In essence we have made a GC column using the adsorbent resin as the column packing in the short desorption tube. Helium was used as the carrier gas and a flame ionization detector was used for the detection of the eluted organics at GC temperatures between 0 degrees C and 360 degrees C in 20 degree increments. Approximately one milligram of each of the analytes was injected in the GC injection port. Carrier gas flow rates were accurately adjusted and measured using a primary flow calibrator (Gilibrator TM, Gilian Instruments) between 1.0 mL/min and 500 mL/min to obtain retention times between 0.1 and 5.0 minutes. The GC oven temperature was accurately controlled to within 5 degrees C using the GC oven temperature controller. From this data the breakthrough volumes were determined by multiplying the retention time by the gas flow rate through the adsorbent resin and dividing this value by the weight of the adsorbent resin (Figure # 2).

Calculation of Breakthrough Volumes

Figure 2 - Calculation of Breakthrough Volumes

A correction was made for the dead volume of the packed tube and connecting plumbing by injecting a non retained volatile at high temperature. A minimum of 7 temperature data points were determined experimentally in triplicate for each of the analytes studied on each resin. This data was used to construct a plot of the log of the breakthrough volume (Bv) versus the analysis temperature (degrees C) This straight line plot was then extrapolated via linear regression analysis to obtain the breakthrough volume at the remaining temperatures (Figure # 3).

Plot of Breakthrough Volumes for Alcohols

Figure 3 - Breakthrough Volumes of Alcohols on Tenax® TA

Finally from this data the Breakthrough Volume tables were assembled. This charts make it much easier to interpret the breakthrough volumes as a function of temperature and to compare different analytes on the same resin as well as compare different resins for the same analyte

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

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