Mass analyzers calibration

Any mass spectrometer requires mass calibration before use. However, the procedures to perform it properly and the number of calibration points needed may largely differ between different types of mass analyzers. Typically, several peaks of well-known m/z values evenly distributed over the mass range of interest are necessary. These are supplied from a well-known mass calibration compound or mass reference compound. Calibration is then performed by recording a mass spectrum of the calibration compound and subsequent correlation of experimental m/z values to the mass reference list. Usually, this conversion of the mass reference list to a calibration is accomplished by the mass spectrometer s data system. Thereby, the mass spectrum is recalibrated by interpolation of the m/z scale between the assigned calibration peaks to obtain the best match. The mass calibration obtained may then be stored in a calibration file and used for future measurements without the presence of a calibration compound. This procedure is termed external mass calibration. 

Note The numerous ionization methods and mass analyzers in use have created a demand for a large number of calibration compounds to suit their specific needs. Therefore, mass calibration compounds will occasionally be addressed later in the chapters on ionization methods. It is also not possible to specify a general level of mass accuracy with external calibration. Depending on the type of mass analyzer and on the frequency of recalibration, mass accuracy can be as high as 1 mmu or as low as 0.5 u. 

The mass analyzer should be calibrated on a regular basis by infusing a calibration solution. In general, an electrospray ionization source (ESI) is used. The solution should produce ions (with known exact masses) that cover the entire instrument mass range or at least the mass range that will be used for subsequent analyses. 

MS Calibration. In the second step, the MS in the ESI mode is calibrated using the calibration solution. All mass analyzers must be calibrated. For example, quadrapoles 1 and 3 are both calibrated for the triple-quadrupole mass spectrometer. Here is the calibration process ... 

A static calibration is used to accurately park the quadrupole mass analyzer on a specific mass of interest. If only a static calibration is performed, the instrument is calibrated for acquisitions where the quadrupoles are held at a single mass as in SIM or SRM. 

An easy calibration strategy is possible in ICP-MS (in analogy to optical emission spectroscopy with an inductively coupled plasma source, ICP-OES) because aqueous standard solutions with well known analyte concentrations can be measured in a short time with good precision. Normally, internal standardization is applied in this calibration procedure, where an internal standard element of the same concentration is added to the standard solutions, the samples and the blank solution. The analytical procedure can then be optimized using the internal standard element. The internal standard element is commonly applied in ICP-MS and LA-ICP-MS to account for plasma instabilities, changes in sample transport, short and long term drifts of separation fields of the mass analyzer and other aspects which would lead to errors during mass spectrometric measurements. 

Fig. 2. Mass spectrometer with photoionization 1—built-in hydrogen lamp 2—vacuum monochromator filled with hydrogen 3—LiF window 4—ionic source container 5—photoionization space with the accelerating grids 6—fluorescent layer for intensity calibration of the incident u.v. light 7—photomultiplier 8—magnetic mass analyzer 9—electron multiplier.

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio (,m/z) of gas-phase ions formed from molecules ranging from inorganic salts to proteins. The mass spectrometer is a device or instmment that measures the mass-to-charge ratio of gas-phase ions and provides a measure of the abundance of each ionic species. To measure the m/z of ions, the mass analyzer and detector must be maintained under high-vacuum conditions and calibrated using ions of known m/z. As explained in the following section, some ion sources can be maintained at atmospheric pressure, while others require vacuum conditions. 

Mass Calibration The process by which the mass analyzer is calibrated such that a measured and displayed m/z is accurate. Well-characterized calibration compounds are utilized, and measured m/z values for these compounds are compared to theoretical m/z values. Calibrants commonly used include various polymeric species (such as polypropylene glyol, or PPGs poly tyrosine (poly-t)) or fluorinated species (perfluorokerosene or PFK) but can be any compound or mixture (Nal/KI) of compounds properly characterized for MS. 

Calibrate the mass analyzer with the multicharged ions of at least three to five standard peptides or following Note 15. 

Fig. 17. A commercial configuration of high-speed gas chromatography-differential mobility spectrometry (GC-DMS) is the Defender (flow schematic top left, instrument top right), which is a successor of the EGIS and EGIS II explosives analyzers. Calibration curve of trinitrotoluene (TNT) (bottom left) and ethylene glycol dinitrate (EGDN) (bottom right) (signal vs. mass in...

A pharmaceutical product, P, is made in a batch reactor. The reactor effluent goes through a purification process to yield a final product stream and a waste stream. The initial charge (feed) to the reactor and the final product are each weighed, and the reactor effluent, final product, and waste stream are each analyzed for P. The analyzer calibration is a series of meter readings, R. corresponding to known mass fractions of P, xp. 

ToF analyzers are relatively small and of medium expense and so represent a good alternative to magnetic sector and ( analyzers, especially when their speed and sensitivity advantages are considered. Their mass accuracy and ease of calibration are also well established. ToF analyzers also have the highest practical mass range of all mass analyzers. However, the digitizer speed may place limitations on the instrumental dynamic range. The very fast acquisition rates that are achieved in ToF analyzers mean that they are also ideally suited... 

In the SIMS technique, an oxygen or cesium ion beam incident on the sample, sputters atoms from the surface. Either negatively or positively charged ions are mass analyzed and their density displayed as a function of sputter time. By using calibration standards, the density is calibrated as concentration/cm, and by measuring the sputter crater depth/ the time axis is converted to a distance axis, giving a dopant concentration vs. depth plot. 

In almost every system, the Mettler Thermoanalyzer I was coupled to a quadrupole mass spectrometer, such as is illustrated in Figure 8.14 (37. 69i. The sample may be studied under vacuum 10"6 Tom or under higher pressures to 1 atm. The reaction chamber, R. is surrounded by the furnace and separated from the balance by a diffusion baffle. The evolved gases pass directly to the mass analyzer. F. which is connected to a recorder, J. through the mass spectrometer control panel. Total pressure is determined by an ionization gauge, S, which also permits the recording of the EGD curve (in this case, due to the pressure change in the system). The relation between measured total pressure and the ion current of the calibration gas permits calibration of the mass spectrometer in absolute partial pressure units or A/Torr. 

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