Calibration ions

Note Besides from elongated deteetion intervals, mass aeeuraey of FT-ICR-MS also benefits by a faetor of 3-10 from internal mass ealibration compared to external calibration (Chap. 3.3.5). External calibration works the better, the closer the cyclotron radius and the number of calibrant ions fit the conditions of the intended analytical measurements. [200]... 

When it is necessary to issue a complete new test report or calibr ion certificate, this shall be uniquely identified and shall contain a reference to the original that it replaces... 

It is because it is implicitly attempting to represent all these various aspects of the real situation inside an ionic solution that the experimentally calibrated ion size parameter varies with concentration. Of course, a certain amount of concentration variation of the ion size parameter is understandable because the parameter depends upon the radius of soivated ions and this time-averaged radius might be expected to... 

Figure 4. Internal standardization of high-mass samples. The spectrum of the chimeric monoclonal antibody, BR96 (0.64 pmol/mm ), was mass calibrated using the singly and doubly charged species of BAD, which was present as an internal standard (0.5 pmol/mm ). Asterisks indicate BAD calibration ions.

Parker, Tice, and Thomason [97PAR/T1C] measured the Ca activity in solutions containing total Ca concentrations in the range 20 x 10 to 200 x 10 M and the selenate concentration 0.004, 0.01, or 0.03 M with a carefully calibrated ion-selective Ca electrode. Activity coefficient corrections were made by Davies equation. The equilibrium constant of the reaction ... 

Mass calibration establishes the mass scale by determining the relationship between a series of miz values, covering the mass range of interest, and the operational parameters that determine how a mass spectrum is collected, e.g., scanning of voltages on a set of quadrupole rods, or measurement of the flight times of ions in a TOF analyzer. Figure 3.1 illustrates a series of calibration ions as well as ions for an unknown and a lock mass. 

The lock mass does not have to be one of the calibrant ions, but it has to be a compound with a known empirical formula. 

A MALDI-FT-MS-based automated system for rapid screening of a large array of compounds is also available [109]. In this approach, the library compounds were mixed with a suitable matrix and were deposited on an auto-indexed multiple-sample disk. The matrix-sample mixture was ionized by irradiation with UV nitrogen laser (337 nm), and mass calibrant ions were generated by electron ionization of perfluorotributyl amine. 

Quantification and Calibration Ions at m/z 104 and 54 corresponding to styrene and butadiene monomers in the LA-FTICR-MS may be used to perform quantification. Figure 47.5 reports the relative... 

Each analyte must meet retention time parameters as established by a laboratory, e.g., ( 2% of calibrators). Ion ratio characteristics (e.g., 30% of calibrators) must also be met. Quantitation is based on response of the analyte of interest to the internal standard response compared to the same ratios that generate the calibration curve. 

External calibration is most effective when the level of excitation and the number of trapped ions of calibrant ions closely approaches that of the analyte ions [188]. The latest FT-ICR instmments can routinely attain mass accuracies of better than 1 ppm. Internal calibration can yield further improvement. 

Fig. 1 Schematic diagram from Piroda, 1955. The helium atoms (1) strike the gold target with Es-253 on the back side (2), recoiling product atoms are collected on the gold catcher foil (3), symbolically dissolved in crucible (4) and separated on a pre-calibrated ion-exchange column (5) and measured in the detection and recording system (6), and (7)...

The carrier gas flow setting of the GC also can show effect on the position of the mass calibration. Ion sources with small volumes and also ion trap instruments with internal ionization show a significant drift of several tenths of a mass unit if the carrier gas flow rate is significantly changed by a temperature program. 

Table 4.17 MRM method setup using two transition for each compound, one for quantitation, the second one for confirmation by checking the calibrated ion ratio.

The interrogation module is the link between experimentalist and the computer. It can be programmed to provide a variety of functions. Some of these options are indicated in the flow chart shown in Figure 6. The first option is the sorting of those ions used in obtaining a mass calibration, converting TOF values into miz values. In the experiment used in the illustration, a decision was made to use the sodium and hydrogen ions as calibration ions, and it was determined by previous measurements that the TOF values for these ions were in time windows of 980 10 ns and 1880 10 ns respectively. TOF values were stored... 

What comes out of the interrogation interface is stored in a computer. For the insulin measurement being used for illustration, the TOF values for the calibration ions are identified by the interrogation module and stored in a separate computer file which sorts by TOF value and records the frequency distributions of TOF values. All other TOF values are truncated to 1 ns resolution and stored in a file that will be used to generate the mass spectrum over the recorded mass range. The sequence of events is depicted in Figure 7. 

Figure 6 Features of event-by-event analysis. The data from the digitizer are sorted according to the objective of the experiment. A standard PD MS analysis involves identifying the calibration ions and storing the data with 78 ps resolution. The data for other ions are truncated to 1 ns resolution and stored. Examples of other software-controlled options are also listed.

Figure 7 Example of the ion sorting process. The software has identified ions 1 and 2 in the event depicted in Figure 4 as H and Na calibration ions and has stored these data In separate files. It then truncates the TOF values tor all five ions and stores these data in a separate file that will be used to generate the full mass spectrum. This process is repeated 2000 times per second over a period of a few hours. The mass spectrum is a composite of the accumulation of the ions emitted from 10 to 10 x 10 fission tracks.

After the analyses of the calibration standards are complete, integrate the peak area of each calibration component and internal standards using the reconstructed ion chromatogram (RIC) of the characteristic calibration ion listed in Table 2. Obtain the area under the extracted ion at the retention time of the expected aromatic component (or internal standard). 

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