三重四极杆液质联用仪基础知识和食品安全中的应用.PPT

* If nitrogen is utilized as the sheath and auxiliary gases with atmospheric vapor (water) present in the APCI ion source, then the type of primary and secondary reactions that occur in the plasma region are as follows: The most abundant secondary cluster ion is (H2O)2H+, along with significant amounts of (H2O)3H+ and H3O+. The reactions listed above account for the formation of these ions within the gas-plasma.The protonated analyte ions are then formed by gas-phase ion-molecule reactions of these charger cluster ions with the analyte molecules (given in Slide #18). This results in the abundant formation of [M+H]+ ions. * * Atmospheric Pressure Photo-Ionization (APPI) is another soft ionization technique. In APPI, ions are generated from molecules when they interact with a photons given off by a UV-light source. APPI generates molecular ions [M+] and protonated molecular ions [M+H]+ for analytes that have an ionization potential below the photon energy of the light source. * APPI分子离子峰很特殊，【M】＋和【M＋H】＋ * * * * * Because of the symmetry of the quadrupole, the x and y stability regions are identical and opposite in sign. When ions are stable in both the xz and yz planes, they will pass through the mass filter. We scan close to the apex indicated at az = 0.24 and qz = 0.706 so that when any given m/z is at this point, higher mass ions will be unstable at lower qs in one plane and lower mass ions will be unstable at higher qs in the other plane. This then leaves only the m/z of interest to pass through the quadrupole. * * Stability diagram of different masses. The RF/DC scan line is shown in red overlaying the stability regions of three different masses plotted in RF and DC instead of a and q. Full scan and SIM * Molecular ions and fragment ions are accelerated by manipulation of? the charged particles through the mass spectrometer.?? Uncharged molecules and fragments are pumped away.? The quadrupole mass analyzer in this example uses positive (+) and negati