High Selectivity in Real Time with SIFT-MS
Until the advent of SIFT-MS, rapid analysis – typically utilizing direct mass spectrometric, spectroscopic or ion mobility techniques – invariably compromised selectivity.
To analyze samples both rapidly and selectively, Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) combines:
- Ultra-soft chemical ionization ensuring consistent, clean spectra.
- 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–. These are all conveniently generated from moist or dry air.
SIFT-MS ionization is much softer than traditional analytical instrumentation that uses 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 (EI-MS) (a) without and (b) with 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.