Industry: Environmental
Instrument: 3100 Purge and Trap Sample Concentrator
Low-level Analysis of Sulfur Compounds in Beer by Purge and Trap
The Analysis of drinking and raw source water for volatile organic impurities and priority pollutants (Methods 524.2 and 624) can be performed using several techniques. In the past, the analysis required either a narrow bore column with a Cryofocusing Module or a wide bore column with a jet separator. The Cryofocusing Module refocuses the analytes onto the head of the column during desorption. This refocusing requires liquid nitrogen. Wide bore columns require a jet separator when interfaced to a bench top mass spectrometer. Jet separators, which pump away excess flow, are notorious for clogging, lowering sensitivity and require an additional vacuum pump. The increased emphasis on avoiding both jet separators and liquid nitrogen led to the development of a new technique for this analysis.
The new technique involves splitting the sample as it is transferred from the purge and the trap concentrator to the column. The gas flow (total flow) desorbing the trap is approximately 20 ml/min. The analytes are very rapidly removed from the trap and sent through the transfer line to the injection port. In the injection port, a large portion of the sample is split out the split vent while less than 1 ml of flow enters the column. The column chosen for the analysis is a short, narrow bore column (0.18 mm x 20m). This technique allows the optimization of the desorb flow independently from the carrier gas flow. The trap is desorbed at an optimal flow rate of 20 ml/min. while still allowing an acceptable flow (0.5 ml/min.) into the column and bench top mass spectrometer.
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