GB/T 38521: Evolution and historical versions
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Gas analysis - Purity analysis and the treatment of purity data
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Basic data | Standard ID | GB/T 38521-2025 (GB/T38521-2025) | | Description (Translated English) | Gas analysis - Purity analysis and the treatment of purity data | | Sector / Industry | National Standard (Recommended) | | Date of Implementation | 2026-03-01 | | Older Standard (superseded by this standard) | GB/T 38521-2020 | GB/T 38521-2020: Gas analysis - Purity analysis and the treatment of purity data---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Gas analysis - Purity analysis and the treatment of purity data
ICS 71.100.20
G86
National Standards of People's Republic of China
Gas analysis purity analysis and purity data processing
(ISO 19229.2015, IDT)
2020-03-06 released
2021-02-01 implementation
State Administration for Market Regulation
Issued by the National Standardization Management Committee
Table of contents
Foreword Ⅰ
Introduction Ⅱ
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Symbol 1
5 Principle 1
6 Impurity analysis 3
7 Use of purity data 6
Foreword
This standard was drafted in accordance with the rules given in GB/T 1.1-2009.
The translation method used in this standard is equivalent to ISO 19229.2015 "Gas Analysis Purity Analysis and Purity Data Processing".
The Chinese documents that have consistent correspondence with the normatively cited international documents in this standard are as follows.
---GB/T 10628-2008 Gas analysis calibration gas composition determination and calibration comparison method (ISO 6143.2001,
IDT)
---GB/T 14850-2020 Gas Analysis Vocabulary (ISO 7504.2015, IDT)
---GB/T 27418-2017 Measurement Uncertainty Evaluation and Expression (ISO /IEC Guide98-3.2008, MOD)
This standard was proposed by the China Petroleum and Chemical Industry Federation.
This standard is under the jurisdiction of the National Gas Standardization Technical Committee (SAC/TC206).
Drafting organizations of this standard. Southwest Chemical Research and Design Institute Co., Ltd., Dalian Date Gas Co., Ltd., Guangdong Huate Gas Co., Ltd.
Company, Tianjin Lianbo Chemical Co., Ltd., Chongqing Institute of Metrology and Quality Inspection, Beijing Huayu Tongfang Chemical Technology Development Co., Ltd.,
Xiamen Huace Testing Technology Co., Ltd., National Coalbed Methane Product Quality Supervision and Inspection Center, Henan Institute of Metrology, East Fujian
Nandian Chemical Co., Ltd., Gansu Institute of Metrology, Hubei Heyuan Gas Co., Ltd., Shenzhen Power Supply Bureau Co., Ltd., Shanghai Huaai
Chromatography Analysis Technology Co., Ltd., Hubei Institute of Standardization and Quality, Xi'an Dingyan Technology Co., Ltd.
The main drafters of this standard. Qu Qing, Shi Liyu, Zhang Wen, Li Fufen, Hu Delong, Wang Shaonan, Chen Yali, Liao Hengyi, Chen Yanshan, Peng Xiujuan,
Liu Yonggang, Jiang Luo, Liu Wenqiu, Jin Naining, Wang Qiang, Li Jia, Wang Lianhua, Du Dayan, Tang Feng, Fang Hua, Liu Chang, Wang Bing, Shi Zhaoqi, Ren Lei, Chen Chunyu,
Zhao Shuide and Tan Yiling.
Introduction
The use of purity data to calculate the composition of the calibration mixture is an important element for establishing the traceability of the certified gas composition measurement. Purity analysis usually
Very challenging, because under normal circumstances, it is necessary to determine various trace components in the feed gas, but the available measurement standards are limited or
This does not exist.
In many practical situations, some form of purity data can be obtained. For the preparation of the calibration mixture, it is particularly important to combine these purity
The information is explained in a unified way and used in the calculation of the mixture composition.
Gas analysis purity analysis and purity data processing
1 Scope
This standard specifies the purity analysis requirements of the raw materials used in the preparation of the calibration gas mixture, and the purity data in the prepared gas mixture group.
Into the application of calculation.
2 Normative references
The following documents are indispensable for the application of this document. For dated reference documents, only the dated version applies to this article
Pieces. For undated references, the latest version (including all amendments) applies to this document.
ISO 6143 Gas Analysis Calibration Gas Composition Determination and Calibration Comparison Method
ISO /IEC Guide 98-3 Measurement Uncertainty Part 3.Guidelines for Expression of Measurement Uncertainty
3 Terms and definitions
The terms and definitions defined in ISO 7504 apply to this document.
4 symbols
The following symbols apply to this document.
i Composition of mixed gas
j Raw material gas
k Specific components in mixed gas
Lij The detection limit of component i in feed gas j
u Standard uncertainty
wij Mass fraction of component i in raw gas j
xij is the fraction of the component i in the feed gas j
ϕij The volume fraction of component i in feed gas j
5 Principle
5.1 Overview
The determination of impurities in all raw materials (gas or liquid) used in the preparation of mixed gases has the same uncertainty for the concentration of components
Certain impact.
There are different ways to evaluate and list all the impurities that may be present in the raw materials, including.
---Open literature information;
---Information attached to raw materials;
---Past experience using the same or similar raw materials;
---Knowledge of raw material production process.
For the finished mixed gas, it should be pointed out which impurities that may exist in the raw materials are "critical" impurities and which are "important" impurities to confirm
Determine the degree of purity analysis required.
5.2 Assessment of key impurities and important impurities
5.2.1 Critical impurities
Impurities that meet one or more of the following conditions are called key impurities.
---The impurities present in the gas or liquid raw materials used in the mixed gas are also a low concentration trace in the mixed gas
Components;
Example 1.If a low-content nitrogen-oxygen mixed gas is prepared, oxygen impurities may also exist in nitrogen.
--- Impurities that may affect the analysis and inspection results of the mixed gas composition;
Example 2.When a gas chromatograph equipped with a non-selective detector is used to detect nitrogen or oxygen containing argon impurities, the presence of the impurity argon will affect the oxygen
Assay results.
--- The impurities present in the raw material gas or raw material liquid used in a multi-component mixed gas are also a kind of micro
Quantity component;
Example 3.In the preparation of natural gas calibration mixture, it is often found that n-pentane and neopentane contain isopentane impurities, and isopentane itself is also a natural gas mixture.
A trace component of combined gas.
--- Impurities that may react with other components in the mixed gas.
Example 4.If a mixed gas of nitric oxide in nitrogen is prepared, the oxygen impurities in nitrogen may react with nitric oxide to form nitrogen dioxide.
5.2.2 Important impurities
Impurities that contribute more than 10% to the expected uncertainty of the concentration of any component in the calibration mixture are called important impurities. weight
The determination of impurities needs to be related to the preparation method used (such as weighing method, volume method, static method or dynamic method) and the various steps involved
The uncertainty of is understood.
The above process is summarized as a flow chart, as shown in Figure 1.The following chapters explain the use of the flowchart.
a If there are unexpected or unknown impurities during the purity analysis, return to the beginning of the flow chart.
b If possible, purity analysis with traceability is preferred over reference purity analysis.
c If possible, traceability or reference purity analysis is preferred.
Figure 1 Flow chart of purity analysis
6 Impurity analysis
6.1 Overview
The degree of purity analysis depends on the analysis result of Flowchart 1.Each level is detailed in 6.2~6.4.
Every possible impurity listed should be analyzed according to flow chart 1.Purity analysis can use one or more suitable
analytical skills. In some cases, multiple analysis techniques may be more needed.
Example. In the analysis of methane, the hydrocarbon impurities can be determined more accurately by gas chromatography (GC-FID) equipped with flame ionization detector.
Other impurities should be detected by gas chromatography equipped with thermal conductivity detector (GC-TCD) or discharge ionization detector (GC-DID).
For some raw materials (such as liquids or corrosive gases), it may not be feasible to analyze their "pure" substances. In this case, you can use
Other methods, such as screening high-purity gases with known purity as the bottom gas, and using weighing methods to prepare lower-concentration mixed gases for purity
analysis. However, this method has an adverse effect on the minimum detection concentration of raw materials. Therefore, when calculating the purity of the target component, attention should be paid to
The purity of the gas.
When using liquid or liquefied gas to prepare mixed gas, the purity of the liquid phase rather than the gas phase should be analyzed. If the gas phase part is used, then
The gas phase should be analyzed. Since the composition of the gas phase and the liquid phase are different, its composition may change with the use of gas or liquid. should
Take appropriate measures to ensure that the obtained raw material purity analysis results are within the specified uncertainty range.
When performing purity analysis, attention should be paid to check for any "unexpected" impurities (according to the assessment step in 5.2, it has not been identified as possible impurities.
quality). For example, when using gas chromatography analysis, unexpected impurity peaks can be seen in the chromatographic peaks. If one or more unexpected impurities are observed,
Should evaluate whether each impurity is a "critical" and/or "important" impurity according to flow chart 1, and carry out corresponding impurity analysis.
6.2 Purity analysis with traceable results
In order to make the purity analysis results traceable, the analyzer is calibrated with a calibration gas mixture with a known uncertainty.
Direct gas comparison (such as the method described in ISO 6143) quantifies impurities.
If quantifiable and traceable purity data can be obtained through other channels (such as analysis reports), the data can be used directly. If provided
If the certificate or report does not clearly state the traceability of the data, it should be evaluated. These evaluations should include but not limited to. whether to use
With the use of certified reference materials or other measurement standards, whether all steps of forming the measurement results are strictly evaluated for uncertainty.
Note 1.The standard mixed gas has good measurement characteristics, and its component concentration can be traced to the country through an uninterrupted comparison chain with specified uncertainty
Or international measurement standards. For example, mixed gases tested by an ISO /IEC 17025 accredited calibration laboratory.
Note 2.When traceable gas measurement standards cannot be obtained, liquid certified reference materials/standard samples with certified purity can also be used.
Note 3.When suitable measurement standards or certified reference materials/standard samples are not available, the preparation plan needs to be redesigned to avoid traceability analysis.
Such as the use of higher purity raw materials.
Note 4.When traceable measurement standards or certified reference materials/standard samples are not available, sometimes the standard addition method can be used to calculate the raw material
purity. Prepare a series of standard materials containing different concentrations of "pure" raw materials, and extend the analysis curve to the coordinate axis to calculate the purity of the raw materials.
6.3 Reference purity analysis
In the field of gas analysis, reference purity analysis is the analysis of the data provided without measurement traceability. This situation may stem from
The following reasons.
---Analysis using a mixed gas whose composition has not established metrological traceability;
---Part of the data uses theoretical response factors;
---Using the spectral line intensity provided by a database that has not established metrological traceability;
---Data obtained from an analysis certificate that does not clarify metrological traceability.
All data that has not established metrological traceability can be regarded as "reference data", and these data can be used for reference purity analysis.
When expressing the results of the reference purity analysis, any possible bias in the data should be dealt with, or an appropriate uncertainty group should be given
In order to explain the possible bias, or correct the bias.
Gas producers usually use some indicators to quantify the purity of pure gas (see the example of high-purity nitrogen in Table 1). These indicators may be derived from
Analytical ability based on purity analysis, or from monitoring the production process.
If the content of a certain impurity that may exist in the pure raw gas is lower than the detection limit of the analytical method used for purity analysis, the manufacturer gives
The detection limit data is usually quoted in the indicator.
In this case, the expected amount of impurities xij should be set to half of the detection limit Lij of the analytical method, as shown in formula (1).
6.4 No purity analysis
For impurities that are neither critical nor important, no analysis is required.
6.5 Estimation of the amount and fraction of substances for which impurities are not detected (but expected to be present)
Sometimes, certain impurities may be expected to be present in the raw material (through empirical knowledge or information provided by a third party, such as the manufacturer of the raw material),
However, when performing traceability or reference analysis, the impurity cannot be detected by the analytical method used, or its content is lower than the detection limit of the analytical method.
In this case, if there is no more suitable and/or more sensitive analytical method, the amount of substances that may be impurity is expected
It can be set to half of the detection limit of the analytical method.
The uncertainty of undetected impurities obtained by using this method obeys a rectangular distribution from zero to the detection limit of the analytical method, that is,
In other words, it is assumed that the probability of the impurity content in the raw material between zero and the detection limit is equal. Therefore, the undetected impurities obey the rectangular probability score
The standard uncertainty is determined by formula (2).
7 Use of purity data
7.1 Calculation of the amount fraction of the main components
The mass fraction of the main components in the analyzed raw materials is calculated by formula (3).
The standard uncertainty of "pure" substances expressed as a fraction of the amount of substances uses the uncertainty specified in ISO /IEC Guide 98-3 (GUM)
The degree transfer rule is calculated, as shown in formula (4).
The uncertainty evaluation of the amount of each impurity substance should consider all relevant factors. These factors may include, but are not limited
Therefore, the uncertainty of the calibration standard, the repeatability and reproducibility of the analysis, the relative response factor used.
7.2 Calculation of the mass fraction of the main component
From the measurement standard or certified reference material used in the purity analysis, the purity data obtained may be expressed in mass fraction, and the quality of the main component
The quantity ratio score wkj is calculated by formula (5).
If it is necessary to give molar-based purity data (amount fraction of substance), the mass fraction and mass fraction of all key and important impurities should be known.
For the related standard uncertainty, data conversion and uncertainty evaluation are carried out in accordance with ISO 14912.
7.3 Calculation of the main component volume fraction
For gases, the purity data is usually given in volume fraction ϕ. In some cases, the given component content is less than a specific value,
The method in 6.3 can be used to estimate the volume fraction of components and their associated standard uncertainty. At this time, Lij represents the upper limit of the target component.
The volume fraction of the main component ϕkj is calculated by formula (7).
If purity needs to be given in terms of mass ratio, substance amount, or other amounts, data exchange should be carried out in accordance with ISO 14912.
Calculation and uncertainty evaluation.
7.4 Other forms of purity data
If the existing purity data does not give a clear value, these data cannot be used to calculate the content of the component.
Note. These data are often expressed in% (percentage), ppm (parts per million) or ppb (parts per billion), and no corresponding values are given.
If the amount of purity data given is different from the expected amount, it should be converted in accordance with the provisions of ISO 14912, and follow-up
Evaluation of measurement uncertainty during calculation.
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