To analyze samples both rapidly and selectively, Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) combines:
- Ultra-soft chemical ionization (which ensures consistent, clean spectra) with
- Multiple reagent ions (that ionize samples using diverse reaction mechanisms and can be instantaneously switched using a quadrupole mass filter).
In SIFT-MS, the chemical ionization (CI) agents are called “reagent ions” (or “precursor ions”). The standard reagent ions used in SIFT-MS are H3O+, NO+, O2+, O–, O2–, OH–, NO2–, and NO3–, and are all conveniently generated from moist or dry air.
SIFT-MS ionization is much softer than traditional analytical instrumentation utilizing electron impact (EI) ionization (e.g. gas chromatography mass spectrometry, GC-MS). The following diagrams illustrate the differences between traditional GC-MS analysis and SIFT-MS for a 15-component gas mixture.
In the first figure, the sample is analyzed using electron impact mass spectrometry without (a) and with (b) GC. A high degree of fragmentation arises from EI ionization. Without GC, EI-MS is complicated and few compounds are resolved. However, the same mode of ionization applied in GC-MS enables compounds to be separated in time through the GC column (hence slowing analysis), while the relatively unique mass spectral “fingerprints” of each compound can be used to identify and quantify the compound.
SIFT-MS applied to analysis of the same mixture resolves all fifteen compounds in real-time without using chromatography – even when just the three positively charged SIFT-MS reagent ions (a) H3O+, (b) NO+, and (c) O2+ are utilized. Red numbers identify unique ions useful for quantitation.
The benefits derived from the unique soft ionization technology employed in SIFT-MS are:
- Unparalleled breadth of analysis
- Very high selectivity in real-time due to near-instant switching of the quadrupole, and
- Extremely slow or no reaction with the major components of air – so you don’t need a column or a membrane to filter them out and can directly analyze the trace components.