The Water Xevo G2-XS Quadrupole Time-of-flight (Q-Tof) is a discovery-based mass spectrometer that combines quadruple technology with a time-of-flight mass analyzer. This provides the instrument with the ability to obtain mass to charge ratios of all compounds in a sample. When coupled with a liquid chromatography (LC) system, non-volatile organic compounds (NVOCs) can be detected.
The sample is injected vis liquid chromatography into a solvent stream which is known as the mobile phase. This mobile phase is pumped through a column containing a stationary phase of coated porous nonpolar particles. When the mobile phase containing the sample solution reaches the column, the analytes of the sample will interact with the stationary phase. The analytes will move through the stationary phase based on their polarity, so the nonpolar analytes in the sample will emerge from the column last, while the polar analytes will leave the column first. Once the analyte/mobile phase mixture leaves the stationary phase, it enters a mass spectrometer via electrospray infusion. In the quadrupole, there is an ionization source that will evaporate the mobile phase leaving the analyte molecules. These molecules are vaporized, ionized, and specific ions are selected based on their mass-to-charge ratio (m/z) before entering the second quadrupole. Here, a collision cell is located where the desired ions are separated from interfering ions using helium gas.
The desired ions exit the collision cell and enter a region that shapes the beam of incoming ions parallel by electrostatic manipulation. The more parallel the beam, the higher the resolving power. After beam shaping, the ions are passed into the time-of-flight mass analyzer. Here, the beam passes into a stack of plates (ion pulser) where a voltage is applied to the back of the first plate to accelerate the ions through the pulser. As the ions leave the plates, they enter a flight tube where at the end is a two-stage electrostatic ion mirror that causes the ions to travel back toward the ion pulser to the detector. The lighter ions will accelerate faster down the flight tube toward the detector. This allows analytes to be separated further and quantified.
Q-Tof is used as an initial screening tool to detect and identify NVOCs that may cause device failure during toxicological risk assessments. It can be combined with GC-MS to detect compounds that are of a non-volatile nature, but LC-MS is still preferred for verifying exact concentrations.