What Is a Sorbent Tube?

Paul Scott

A sorbent tube is a glass vial filled with specialized absorbent materials used to test the atmospheric concentrations of specific substances including hazardous gases. The tubes are used in conjunction with a specially-calibrated pump which draws air from the test atmosphere through the tube at a controlled rate. Target substances present in the air are trapped in the relevant absorbent materials. After sampling, the tube is sealed and sent to a laboratory for analysis. There are several sorbent tube classes each containing a specific selection of absorbent materials used to test for different groups of airborne contaminants.

The contaminants trapped in a sorbent tube are analyzed in a laboratory.
The contaminants trapped in a sorbent tube are analyzed in a laboratory.

Exact concentrations of hazardous contaminants such as gases and fumes in the air are often difficult to ascertain with any degree of accuracy. This can lead to contaminants accumulating to the point where explosions and poisoning can occur. These issues are of particular concern in environments such as mines, chemical plants, and petroleum refineries, where the presence of toxic or explosive gases and fumes are an ongoing operational reality. Although there are various types of sampling and testing devices used to detect these substances, one of the most accurate, and, indeed, one of the most simple, is the sorbent tube.

Consisting of a suction pump and a series of uncomplicated glass tubes restricted on each end and filled with a selection of absorbent materials, or sorbents, the sorbent tube system is certainly one of the most low-tech of all test devices. As simple as they may be, they are one of the most accurate, delivering consistent, reliable contaminant concentration readings. Operation of the system is equally simple, requiring the insertion of an open sorbent tube onto the end of a hollow wand, which is connected via a length of hose to the pump. The open end of the tube is held in the test atmosphere for the timed pump cycle. When the cycle is finished, the tube is sealed and sent to a laboratory to have the contaminants trapped in the sorbents analyzed.

The accuracy of the system is underpinned by the calibrated rate at which the vacuum pump draws air through the tube over a set time frame and the known absorbency rate of the sorbents. A range of tube types, each with a specific combination of sorbents, also lends the system versatility by allowing test atmospheres to be sampled for the presence of a range of target substances. The pumps may also feature a range of pump cycles to suit relevant ambient conditions, tube types, and targeted contaminants.

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