Mass calibration reference list

Some reference compounds for mass calibration are listed below ... 

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. 

Once the mass spectmm of a calibration standard is known and the elemental composition of the ions that are to be included in the mass reference list are established by an independent measurement, a reference list may be compiled. For this purpose, the listed reference masses should be calculated using six decimal places. Otherwise, there is a risk of erroneous reference values, especially when masses of ion series are calculated by multiplication of a subunit. Such a tasks are well suited for spreadsheet applications on a personal computer. 

The final determination of the CBs was performed by capillary gas chromatography with electron capture detection mass spectrometry was used as complementary technique to confirm the identity of each of the CBs determined. Each participant had validated its method by performing experiments on recovery, extraction efficiency, procedure blanks and detector linearity. The seven individual CB calibrants were supplied to the participants as pure, crystalline CRMs from BCR (CRMs Nos. 291,293, 294,295, 296. 297 and 298). Each laboratory was requested to prepare separate calibration solutions of the appropriate concentration, in iso-octane, to calibrate the detector and lying within its linear range. The use of at least one internal standard was mandatory the participants, however, were left free to select the internal standard(s) best suited to their methods. They had to verify that the selected compounds did not occur in the candidate reference material or did not interfere with compounds present in the material. A series of pure dichlorobenzylalkyl ethers (DCBEs) was made available to the participants but other internal standards were also accepted of which the list is given in the certification report [21] along with additional details on calibration procedures. 

Table 2. List of PSL particles used for the calibration of the DMA and APM. a. Density given by the manufacturers as a reference, b. Particle mass was calculated using the diameter range and density.

When purchased, the reference material from which the calibration sources are prepared will be accompanied by a calibration certificate. This will list, for each nuclide, the activity per unit mass and the overall uncertainty on that activity. These uncertainties should then be taken into account when the efficiency calibration curve is created (see Chapter 7, Sections 7.6 and 9.9). Ideally, they would be used to weight the corresponding points within the fitting process. 

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