How to Select an Adsorbent Resin for an Application

The selection of an adsorbent resin for an application is based on a large number of variables. These variables originate from three sources and each area and parameter must be evaluated before a resin is selected.

Purge and Trap Sampling System

Sample Matrix - gas, liquid or solid
Temperature of Sample
Amount of Water in the Sample
Range of Analytes to be Analyzed
Concentration of Analytes in the Sample
Amount of Sample Available
Sample Purge and Trap Flow Rate
Need for Dry Make-up Gas

Adsorbent Resin - Sample Collection Conditions

Breakthrough Volume Data for Analytes of Interest
Bed Volume of Desorption Tube
Affinity of Resin for Water
Sample Collection Flow Rate
Backpressure in the Desorption Tube

Adsorbent Resin - Desorption System Conditions

Desorption Temperature Required to Purge off Analytes
Gas Volume Required to Purge off Analytes
Need for an Initial Purge to Remove Water or other Solvents

Purge and Trap Sampling System

Before an adsorbent resin is selected the sample matrix, the range of analytes required for analysis and the concentration of analytes in the sample must all be considered. In conjunction with this the limits of detection of the GC detector and the amount of sample available for analysis must also be considered. All of these factors are interrelated. Based on the limits of detection of the GC detector and the concentration of analytes in the sample the minimum sample size required for analysis can be determined. Depending on the range of analytes required for analysis the sample collection temperature can be determined. The higher the temperature of the sample the higher the boiling point range of analytes that will be collected. Depending on the temperature of the sample and the amount of water in the sample the sample purge flow rate and need for a dry purge make-up gas can be determined.

When all these factors have been evaluated, the chemist should have determined the sample size required, the sample temperature, the sample flow rate and the purge gas flow rate.

Adsorbent Resin - Sample Collection Conditions

Next based on the data above plus the range of analytes required for the analysis, an adsorbent resin must be selected. The Breakthrough Volume Data tables can be used to help select a resin. For the collection of samples with the desorption tube at room temperature the Breakthrough Volumes for all the analytes of interest should be greater than 10.0 Liters per gram of adsorbent resin. This value can be lowered only if gas volumes less than 5.0 liters per gram of adsorbent resin are used during sample collection. Next the adsorbent resin must be evaluated for its affinity for water. If your sample matrix is water then an adsorbent resin such as Tenax® TA is a good choice. Also the dimensions of the desorption tube including the amount of adsorbent resin that it can hold must be considered. Related to this, the backpressure generated inside the desorption tube must be considered if a small personal sampling pump is used for sample collection.

Adsorbent Resin - Desorption System Conditions

Finally the desorption parameters must be considered. Again the Breakthrough Volume tables are used to determine the temperature required to release the analytes of interest off the adsorbent resin. This temperature must be less that the maximum rated temperature of the adsorbent resin. Related to this is the gas volume required to release the analytes off the adsorbent resin. A desorption temperature must be selected that will release the analytes of interest off the adsorbent resin in less than 10 ml/gram of adsorbent resin.

If the sample contains large solvent peaks that you want to purge off the resin before the normal analysis the Breakthrough Volume Data can again be used to determine the temperature and amount of gas required to purge off these solvents while retaining the other analytes on the adsorbent resin.

All the factors above must be used in conjunction with the Breakthrough Volume Data tables and the Backpressure Tables to select an appropriate adsorbent resin for your application.

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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