Transmission efficiency of ions

Attainable detection limits depend on the amount of analyte that enters the ICP per second, the efficiency of aerosol conversion into analyte ions in the ICP, and the transmission efficiency of ions from the plasma to the MS detector. The detection limits also depend on the variation of the background and the integration time. Typical pneumatic nebulizer/spray chamber systems operated at sample uptake rates from 0.1 to 2.0 mL/min introduce an amount of analyte equivalent to that in 10 to 30 JiL/min of sample solution into the ICP. At a sample uptake rate of 1 mL/min, only 1% to 2% of the analyte enters the plasma most of the sample is lost in the spray chamber and exits through the drain. Concentration based detection limits can be improved by approximately a factor of 10 by using a high-... 

Matrix-Induced Changes in the Transmission of Ions from the Inductively Coupled Plasma to the Mass Spectrometer Detector. The most severe chemical matrix effects in ICP-MS are due to changes in the transmission efficiency of ions... 

Thus 8 measures the product of the ionization efficiency (fraction of analyte molecules delivered as ions to the entrance from the API source into the MS) with the transmission efficiency of ions from the MS entrance aperture to the detector. The first experiments, conducted at flow rates of tens of nL.min, gave 8 values of about 1/1000 (Wilm 1994), later improved to 1/390 (Wilm 1996) using a quadrupole mass spectrometer operated with very high peak widths to improve transmission efficiency the sampling efficiency... 

This mode is executed by scanning or fixing the electric potentials of QMF I in the absence of a collision gas in the collision cell, and operating the QMF II as an ion guide. Under these conditions, the transmission efficiency of ions in the collision cell and the QMF II are optimized by selecting proper electric potentials. 

The signal intensity of a spectral feature depends on multiple factors. The first determining factor is the concentration of analyte before ionization, which is also the amount of the molecule of interest. However, signal intensity depends even more on ionization efficiency - a parameter that is very hard to predict and control. Signal intensity also relies on the transmission efficiency of ions from ion sources to detectors, and the detection efficiency of detectors towards the mass and kinetic energy of incoming ions [11,12]. Since the influence of every parameter on signal intensity is unknown, mass spectra only reveal relative abundances of ions. These relative abundances can be used to estimate absolute abundances and concentrations of analytes in the analyzed samples. 

Relative chemical potentials ion Transmission efficiency of ion source... 

The weakness of MC-ICPMS lies in the inefficiency by which ions are transferred from the plasma source into the mass spectrometer. Therefore, despite very high ionization efficiencies for nearly all elements, the overall sensitivity (defined as ionization plus transmission efficiencies) of first generation MC-ICPMS instruments is of the order of one to a few permil for the U-series nuclides. For most, this is comparable to what can be attained using TIMS. 

Mass bias, or the instrumental mass fractionation, is the variable transmission of the ion beam into the mass spectrometer. A variety of phenomena create conditions that lead to variable transmission of ion beams. For modem instmments, the transmission in the flight tube and the efficiency of ion conversion to electrons at the collector are almost quantitative. Most fractionation processes, therefore, take place within the source, namely in the area where the analyte is introduced into the mass spectrometer and ionized, or at the interface between the source and the mass analyzer. 

A number of optical photoion-photoelectron coincidence experiments have been reported107 giving qualitative information on molecular breakdown. However, in these experiments little or no attempt has been made to correct for either the transmission efficiency of the photoelectron spectrometer or the ion kinetic-energy discrimination. Fragment ions usually... 

The consequences of these boundary conditions strictly limit the secondary Ion transmission efficiency of the Instrument and thus, ultimately, the sensitivity of the analysis. 

The transmission efficiency of MC-ICP-MS is high relative to that of most ICP-MS instruments (>108 ions sec-1 ppm l indium using conventional aspiration methods) but is low relative to that of TIMS. This is because the ions in the plasma... 

The efficient transport of ions through any mass spectrometer is vital, but it is perhaps of special concern within TOF-MS because of the duty factor issues and the excellent transmission efficiencies of which these spectrometers are capable. 

Another significant challenge remains in further increasing the efficiency with which sample species are utilized through increased ion throughput and duty factor. Currently many of the ions generated by continuous ionization sources are lost because of the pulsed nature of the instrument. Realization of higher duty factor and the unit transmission efficiency of which TOF-MS is capable could propel the TOF-MS into a sensitivity realm well beyond that of current mass analyzers. 

Today, MALDI ion mobility MS instruments have longer drift cells and use both ultraviolet (UV) and infrared (IR) laser ionization. In addition, the longer drift cells have nonlinear electric fields, which help to focus the ions into the center of the tube and increase the transmission efficiency of the ion, reducing both resolving power and cross-section accuracy. MALDI ion mobility MS has been used for the analysis of very complex biological samples. Figure 9.5 is a typical MALDI ion mobility MS... 

Perhaps the most spectacular of the early results that demonstrated the potential of FAIMS as a mobility filter for MS was in the detection of nine chlorinated and brominated haloacetic acids at the part-per-triUion levels in drinking water. - The selectivity and efficiency of ion transmission through the FAIMS into the MS improved the detection limits of these compounds by three to four orders of magnitude over conventional ESI-MS methods. 

The transmission efficiency of the analyzer is just one component of the overall sampling efficiency of the instrument, defined as the fraction of analyte molecules delivered to the ion source that are ionized and delivered to the detector obviously the ionization efficiency of the ion source must be considered in addition to the transmission efficiency of the analyzer. Even this does not fully describe the overall efficiency of production of analyte derived signal, since detector response (a function of m/z. 

To take the difference in detection efficiency into account, the transmission factor Fj is introduced, which is the ratio between the transmission efficiencies of both ions. It should be noted that the transmission factor TV is a factor specific for an instrument and depends on the mass. 

Mass analyzers. MALDI is ideally coupled to time-of-flight (TOF) for polymer analysis (17). This combination is ideal due to the pulsed nature of the laser and the theoretically unlimited mass range and high transmission efficiency of TOF. Ions are produced by laser ablation of the dried matrix/analyte mixture and are then accelerated by a fixed potential into a drift tube that does not contain an external electric field. The ions continue moving toward a detector. Since all the ions are accelerated at the same potential, the kinetic energy (KE) of a given ion can be given by eq. 1 ... 

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