Drift voltage

Kanazawa et al. [124] determined omeprazole and its metabolites in human plasma by liquid chromatography-three-dimensional quadrupole mass spectrometry with a sonic spray ionization interface. The analytical column was YMC-Pack Pro Cig (5 cm x 2 mm) using acetonitrile-50 mM ammonium acetate (pH 7.25) (1 4) at a flow-rate of 0.2 ml/min. The drift voltage was 30 V. The sampling aperture was heated at 110 °C and shield temperature was 230 °C. In the mass spectrum, the molecular ions of omeprazole, hydroxyomeprazole, and omeprazole sulfone were clearly observed as base peaks. The method is sufficiently sensitive and accurate for pharmacokinetic studies of omeprazole. 

I, sample injector 2, thermostat 3, multi-capillary column 4, ionization chamber 5, 63Ni source of beta radiation 6, field inlet 7, separation chamber 8, electrodes 9, drift voltage generator 10, electrometer and... 

This cell is typically 4-5 cm long and operates at pressures of 3-5 torr and drift voltages of 10-100 V across the cell. 

The resolution tD/AtD of a drift tube is proportional to the square root of the drift voltage VD across the tube [9] ... 

APCI-MS has been used extensively for the structural analysis of diterpene alkaloids from various Aconitum species for both positional and stereoiosomeric determination [ 57,58]. By controlling the drift voltage between the first and second electrodes in... 

The instrumentation employed by Stapleton and Bowie was an ion cyclotron resonance mass spectrometer that had been modified to permit computer control of all drift voltages and to allow direct reading of the ion transit time (typically 10 to 10 seconds) similar to that described by McMahon and Beauchamp An emission current of about 0.2 microampere and a nominal 70 eV electron beam produced ion currents of 10 to 10 A at source pressures of approximately 10 Torr. The mass spectra were measured by magnetic field modulation. 

Detector MS, Hitachi M-1000, APCI interface, drift voltage 21V, nebulizer 260°, vaporizer 399°, multiplier voltage 1500 VF, m/z 326... 

Another scheme involves modulation of the drift voltages which, by varying the ion transit time, produces modulations in the density of ions in the cell the marginal oscillator records a periodic change in energy absorption which is detected as sm absorption signal at the modulation frequency. 

T can be calculated from the geometry of the ceU and the drift velocity, but ion residence time in an ICR cell is a complex function of many variables. As Smith and Futrell 2 2) have shown experimentally, calculations of residence times are correct only for very low electron currents and trapping voltages. When dc electron currents approach 0.5 [i,A, or when the trapping voltage is equal to or greater than one-half of the drift voltage, the theoretically calculated residence time may be in error by more than 25%. These authors therefore determine the residence time experimentally from the lag time of a pulse sequence and measurements of TIC 200,262) ... 

This is quite different than in a metal, in which an applied voltage allows the mobile electrons to acquire a drift voltage. In a p-n junction, minority carriers are injected into both regions. They were not there originally and arise as a consequence of the applied voltage. 

Substituting that into Equation 1.20, employing Equations 1.11 and 1.9, and defining U, the voltage across the drift distance (the drift voltage), Revercomb and Mason obtained... 

Hence the resolving power of conventional IMS depends only on the drift voltage, gas temperature, and ion charge state, but no other ion property such as mobility or... 

By Equation 2.2, K depends on E at any E. In practice, a quadratic leading term means that the variation of K exceeds the measurement uncertainty and becomes noticeable fairly abruptly above some E/N threshold, as observed in experiment (2.1). At lower E/N, called the low-field limit, K may be deemed independent of E/N. Conventional IMS is usually operated in that regime, as evidenced by linearity of v with respect to E/N varied by changing the drift voltage or gas pressure... 

The ion diffusion along the gap will be controlled by the transverse diffusion coefficient (2.2.4) that is normally smaller than Dn but higher than the zero-field isotropic diffusion coefficient, D. Therefore, the resolving power will be somewhat lower for dispersive IMS-ADD than for DT IMS at equal drift voltage and gas... 

Figure 5.23 Current-drift time curves (ion mobility spectra) recorded using a drift voltage of 4.0 kV, for positive ions formed from a 0.0053 wt% solution of lysozyme in 90 % alcohol, and for the pure solvent, at carrier gas flow rates of 135 and 200mL.s , respectively. Peaks 4 and 5 clearly arise from the solvent, but peaks 1, 2 and 3 were assigned as different charge states of lysozyme. Reproduced from Gieniec, Biomed. Mass Spectrom. 11, 259 (1984), with permission of John Wiley Sons, Ltd.

The resolution of an IMS device depends in practice not only on the spread of ions At due to diffusion in the drift region relative to the drift time t, but also on the drift tnbe-independent spread of the ion cloud, A/ , brought about by the initial width of the ion pulse entering the drift region and the spread of ions after the drift region (e.g., in the ion funnel). Following Equation (1.4), the resolution t/At is affected only by the two parameters temperature T and drift voltage V. 

Measurement of an absolute ion mobility requires knowledge of the drift time t, drift length L, drift voltage V, buffer gas pressure p, and temperature Z All of these parameters can easily be measured with good precision. However, any uncertainty in the parameters t,L,E= V/L, N, and the square root of T [Equations (1.1) and (1.5)] translates directly into an uncertainty in the mobility measurement. 

Experimental Pressure p and Drift Voltage V Values Used to Obtain (CCCCG)H+ Ion Arrival Time Distributions and Average Arrival Times... 

MS mode is typically used when tuning for signal the drift cell is filled with buffer gas to the desired pressure, the drift voltage and injection energy (defined as... 

To obtain different values of P/V it is possible to change one or both of the parameters however, the cell pressure can take several seconds to stabilize when it is changed, while the drift voltage stabilizes almost instantly. It is therefore more... 

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