Optimising an Airborne Gas Chromatograph/Mass Spectrometer to Measure Tropospheric Volatile Organic Compounds

Work to optimise the temperature program of an airborne gas chromatography mass spectrometer was carried out in order to increase the number of analyses that can be carried out per flight. This was done by measuring the amount of time taken by the GC oven to cool from a range of final temperatures to a range of initial temperatures. In addition, experiments were carried out in order to determine how the resolution varied with changing temperature programs. This was done in order to decrease the amount of time the instrument was idle for, increasing the amount of time the instrument spent analysing tropospheric air samples. It was found that the initial temperature had a much larger effect on chromatographic resolution than the final temperature. Increasing the initial temperature from 40 °C by 2-4 degrees yielded a cool down time much shorter than that at 40 °C, with only a slight loss of resolution. The problem of water on the column, seen in chromatograms from the BORTAS field campaign, was also addressed, and a cold trap was developed to freeze water out of air samples.