Detail of GB/Z 42625-2023

Introduction of GB/Z 42625-2023

GB/Z 42625-2023 Vacuum technology - Vacuum gauges - Characterization of quadrupole mass spectrometers for partial pressure measurement 1 Scope This document specifies the characteristics of quadrupole mass spectrometers (QMSs) with an ion source of electron impact ionization and which are designed for the measurement of atomic mass- to-charge ratios m/z<300. This document is not applicable to QMSs with other ion sources, such as chemical ionization, photo- ionization or field ionization sources and for the measurements of higher m/z, which are mainly used to test organic materials. It is well known from published investigations on the metrological characteristics of quadrupole mass spectrometers that their indications of partial pressures depend significantly on the settings of the instrument, the total pressure, and the composition of the gas mixture. For this reason, it is not possible to calibrate a quadrupole mass spectrometer for all possible kinds of use. The characterization procedures described in this document cover the applications of continuous leak monitoring of a vacuum system, leak rate measurement with tracer gas, residual gas analysis and outgassing rate measurements. The user can select that characterization procedure that best suits his or her needs. These characterization procedures can also be useful for other applications. It is also well known that the stability of several parameters of quadrupole mass spectrometers, in particular sensitivity, are rather poor. Therefore, when a parameter has been calibrated, it needs frequent recalibration when accuracy is required. For practical reasons this can only be accomplished by in situ calibrations. To this end, this document not only describes how a quadrupole mass spectrometer can be calibrated by a calibration laboratory or a National Metrological Institute with direct traceability to the System International (SI), but also how calibrated parameters can be frequently checked and maintained in situ. By their physical principle, quadrupole mass spectrometers need high vacuum. By reducing dimensions or by special ion sources combined with differential pumping the operational range can be extended to higher pressures, up to atmospheric pressure. This document, however, does not apply to quadrupole mass spectrometers with differential pumping technology. Therefore, it does not cover pressures exceeding 1 Pa on the inlet flange of the quadrupole mass spectrometer. This document does not describe how the initial adjustment of a quadrupole mass spectrometer by the manufacturer or by a service given order by the manufacturer should be made. The purpose of such an initial adjustment is mainly to provide a correct m/z scale, constant mass resolution or constant transmission, and is very specific to the instrument. Instead, it is assumed for this document that a manufacturer's readjustment procedure exists which can be carried on-site by a user. This procedure is intended to ensure that the quadrupole mass spectrometer is in the best condition for the characterization. It is the intention of this document that the user gets the best possible metrological quality from his quadrupole mass spectrometer. From investigations it is known that in most cases this can be achieved in the so called “scan mode”. The bar graph may also be of an adequate quality depending on the software used for evaluation of the data taken by the quadrupole mass spectrometer. The trend mode, however, often involves the additional uncertainty that a shift of the peak value position on the mass scale causes a shift in ion current. For this reason, the scan mode is preferable for most of the measurement procedures of this document. It is not the intent of this document that all the parameters described be determined for each quadrupole mass spectrometer. However, it is intended that the value of a parameter addressed in this document be determined according to the procedure described in this document if it is given or measured (e.g. for an inspection test). It is assumed for this document that the applicant is familiar with both the operation of quadrupole mass spectrometers and high and ultra-high vacuum technology. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 34873-2017 Vacuum gauges - Calibration by direct comparison with a reference gauge (ISO 3567 : 2011, IDT) ISO 14291 Vacuum technology - Vacuum gauges - Definitions and specifications for quadrupole mass spectrometer Note: GB/T 40333-2021 Vacuum gauges - Definitions and specifications for quadrupole mass spectrometers (ISO 14291:2012, IDT) 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 14291 and the following apply. 3.1 matrix gas gas or gas mixture that makes the major contribution to the total pressure 3.2 equivalent nitrogen pressure pressure of nitrogen which would produce the same gauge reading as the pressure of gas acting on a vacuum gauge [Source: ISO 3529-3:2014, 2.3.5, modified] Note: Nitrogen equivalent depends on the type of gauge, since the relative sensitivity factor is different for different types. For this reason, the term should be used with the type of vacuum gauge. 3.3 transmission probability ratio of ion current of a certain mass-to-charge ratio exiting a quadrupole filter of a QMS to the current of ions of the same mass-to-charge ratio entering it 3.4 scan speed u(△m/z=1) per time with a defined number of signal points per u (△m/z=1) 3.5 linear response range partial pressure range over which the non-linearity is within a specified limit Note 1: For the purpose of this document the limit is ±10% from the mean value. Note 2: The linear response range can also depend on the conversion of the output current signal to a digital value. Sometimes a single digital bit does not quantise the same amount of current at the lower and upper end of the range [Source: ISO 14291:2012, 2.2.18, modified] 3.6 leak rate measurement quantitative measurement of a tracer gas through a leak 3.7 leak rate monitoring continuous monitoring of one or several selected gas species with respect to the normal background in a vacuum system in order to detect a change caused by a leak Example 1: In an accelerator tube, argon is monitored to detect a leak from air. Example 2: In a fusion reactor, water peaks are monitored to detect a leak from the cooling system 3.8 fragmentation pattern pattern (i.e. kinds and relative amounts) of ions produced by a given pure gas in a given mass spectrometer under given conditions Note: This definition does include the isotopic and isomeric distribution of the species. [Source: ISO 14291:2012, 2.2.18, modified] 3.9 interference effect ratio ratio Si'/Si where Si' is the sensitivity of a specified gas species i of partial pressure pi present in an interference gas or interference gas mixture. Si is the sensitivity at the same value of pi when only gas i is present. 3.10 interference gas gas species added to a pure gas that may cause an interference effect 3.11 interference gas mixture mixture of several gas species added to a pure gas that may cause an interference effect 3.12 dynamic range ratio of the largest signal to the smallest signal within a spectrum Note: The difference between minimum detectable concentration (CMDC) as defined in ISO 14291 and dynamic range is that for the CMDC it is acceptable to optimize the signal to noise ratio for the minor constituent, while this is not possible for the dynamic range.

Contents of GB/Z 42625-2023