The US EPA leads Photochemical Assessment Monitoring Stations programs (PAMS) for more than 15 years and many equipments used at PAMS sites are old and need to be replaced. That is why US EPA has conducted a material review of fully automatic GC units able to by analyze the 56 VOC ozone precursors of the PAMS list. They planned to perform an evaluation in two steps :
- Laboratory evaluation of selected units : 8 candidates
- Field evaluation of three selected units after laboratory evaluation : deployment at PAMS field stations.
RTI International based at Research Triangle Park in Durham (North Carolina), has been chosen by the US EPA to organize the tests.
With Consolidated Analytical Systems (CAS), our distributor in the USA who has provided a demo airmOzone unit, we have been selected as one of the 8 candidates. At this time the laboratory phase testing is ended and RTI is currently analyzing the test results of each candidate in order to select the three best units that will be admitted to the field evaluation.
The laboratory phase tests
The testing took place over a period of 3 weeks : first week set up phase in the RTI laboratory, second and third week testing phase.
Two different blends have been chosen : PAMS blend at 100 ppb and Texas Commission on Environmental Quality (TCEQ) blend at 6 ppb. TCEQ is the PAMS blend plus several potential interferent compounds. Both cylinders are diluted using zero air generator and a dilution system with three mass flow controllers (two connected to the cylinders and the other to the generator).
The dilution blend is sent to a manifold where all instrument sample the gas to be analyzed. One TO17 sorbent tube is also connected to the manifold and will be used as reference. Different concentrations and different conditions of temperature (25°C to 35°C) and humidity (20% to 70 %) have been applied during the 9 days of testing.
5 tests were performed each day : zero air test, 3 tests of concentration variation and a last test over the night at a defined concentration between 18h and 4h.
The candidates were required to provide a report of the results of their units before a certain deadline. The list of compounds to be measured has been determined by RTI and corresponds to PAMS list (56 VOC) plus several optional compounds such CCl4, 1,3 butadiene, alpha and beta pinene.
Acetone has been removed from the study because of too much interference. The laboratory evaluation consists also in other evaluation criteria as usability, reliability and cost. Each candidate has been required to fulfill a table indicating information concerning these parameters.
Conclusion of the laboratory tests
CAS / Chromatotec® team wrote reports during each of the 9 days of testing with sensitivity factors stable and logical regardless of the level of dilution, temperature and humidity applied to the sample.
During these tests, we have noticed to RTI several advantages of our unit :
- Compact unit in rack, easily transportable (look at photo here above). We were the only vendor to supply rack mounted system, other units were placed on the laboratory bench
- Autonomous unit regarding the gas supply : air and hydrogen
- Analysis cycle time in 30 mn other units were in 1 h cycle time. This is a considerable advantage when tests last only 1h30. We were able to supply 2 or 3 results when other candidates could obtain only one result.