Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) is widely used in 24/7 monitoring applications due to its key advantages of real-time analysis, and zero sample preparation. Up until recently, the carrier gas used in SIFT-MS instruments to transport the ions along the reaction flow tube has been confined to helium. Here at Syft Technologies we have developed a nitrogen carrier option, which vastly reduces the cost of deployment in these 24/7 applications. It also allows for the use of a nitrogen generator, thus eliminating the use of pressurized gas cylinders. The results of using nitrogen have proven to be as definitive and accurate as for helium.
We tested a range of compounds individually, to determine the effect nitrogen carrier gas had on the ion-molecule reactions that are the key part of SIFT-MS. However, we wanted a more exacting test of the performance of SIFT-MS instruments operating on helium and nitrogen carrier gases. This was provided by analyzing complex samples, like the 41 compound gas standard from the US EPA TO-14A compendium method. The results obtained in full scan mode are shown in Figure 1 and 2.
Figure 1: SIFT-MS spectra generated from H3O+, NO+, and O2+ with EPA TO14A gas standard in helium carrier.
Figure 2: SIFT-MS spectra generated from H3O+, NO+, and O2+ with EPA TO14A gas standard in nitrogen carrier.
Nitrogen carrier gas has very little effect on the reaction kinetics and energetics, as the spectral “fingerprints” are very similar for all three reagent ions. The quantitative measurements between the helium and nitrogen carrier instruments were also in good agreement.