Trace level gases via GC/MS and a unique valve switching concept Permanent gases and CO2 are analyzed and quantified at sub-ppm levels by using a 0.53 mm PoraPLOT Q and a 0.53 mm Agilent Molsieve 5Å PLOT column, which are switched in a special way, as shown in the figure. Using this switching concept, there is no flow reversal in the system and there is only one transfer line from the valve to the mass spectrometer. Injection (position 1) is done on the PoraPLOT Q column where the permanent gases will elute as one peak and the CO2 is retained. The permanent gases are sent to the Molsieve column. This peak includes: neon, nitrogen, oxygen, carbon monoxide, argon and methane. The valve is switched into position 2: the CO2 elutes from the PoraPLOT Q column into the transfer line and is detected by the MS. The permanent gases are separated by the Molsieve column, travel through the PoraPLOT column and elute after the CO2 . The extra transport through the PoraPLOT Q column will only result in a small decrease in sensitivity. To set up the method, the timing of the valve switching is important: CO2 should not enter the Molsieve column because it will be adsorbed. To prevent any disturbance by leaks, all fittings in the system are located in a purged plastic housing on top of the GC, which is kept under a stream of ultrapure helium.
Publication number: A01339.pdf
Publication Date: 11 May, 2010