Utilizing a Purge and Trap Autosampler: An Overview
An autosampler inserts laboratory samples into the inlets of a chromotograph. In the previous, the function of an autosampler was performed by hand. In addition to becoming time consuming, this technique placed samples at risk for contamination, and the operator at risk for coming in get in touch with with dangerous substances such as Volatile Organic Compounds (VOCs). These days, autosamplers have several mechanisms for inserting samples automatically. For VOC analysis, the most useful of these mechanisms is the purge and trap type, which purges compounds from the sample and traps them in the concentrator, where they are heated. Other types of autosampler insertion mechanisms include:
- S/SL injection mechanisms, which insert the sample by way of a syringe via a septum. - On-column inlet mechanisms, which insert the sample into the column with out heating it. - PTV injector mechanisms, which insert a low heat sample at a controlled rate. - Gas source inlet mechanisms, which insert a gaseous sample into the carrier gas stream via a switching valve that connects to a sample loop.
In addition to being mechanically distinguishable from the insertion mechanisms above, this type of mechanism is also distinguishable for its ability to isolate low levels of VOCs and other substances. A purge and trap autosampler is used for measuring substances whose presence can only be detected by a concentrator. This type excels at sequestering trace amounts of substances that other mechanisms would not capture. Water analysis, soil analysis, and food and beverage analysis all use the this method to detect VOCs in infinitesimal amounts.
According to the Environmental Protection Agency's (EPA) "Test Methods for Evaluating Solid Waste, Physical/Chemical Methods" (SW-486), there are two methods for testing a sample for VOC analysis: Purge and Trap Technique 5035B, in which a strong sample must undergo methanol extraction, with an aliquot from the extraction being added to the mechanism and Closed System Purge and Trap Technique 5035, in which the sample is sealed in an airtight vial and then analyzed without breaking the seal.
How the Purge and Trap Technique Works
This technique consists of three steps that happen prior to the compounds being delivered to the column via carrier gas:
- Carrier gas is bubbled through the sample to release its compounds - The compounds are released and trapped in the concentrator - The concentrator is heated until the compounds vaporize
From the column, the vaporized compounds travel to the detector where their traits are analyzed. When the detection process is complete, the outcomes are displayed on the data interface of the chromotograph, and can be recorded by a chart recorder when one is attached.
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