ISO/TC 158 - Analysis of gases

This document specifies the general provisions and gives the basic definitions of terms relating to sampling for gas analysis, including sampling devices, sampling methods, sampling technical considerations, and sampling safety. This document applies to both direct and indirect sampling of gas in pressure receptacles and pipelines, including pure gases and gas mixtures. Compressed and liquefied gases are both considered. This document applies to the sampling of processed gases and does not involve gas treatment processes. The sampling procedures specified are not intended for the sampling of special products which are the subject of other International Standards, such as liquefied petroleum gases (see ISO 4257) and gaseous natural gases (see ISO 10715).

This document gives a brief overview of each of the dynamic techniques which are described in detail in the subsequent parts of ISO 6145. This document provides basic information to support an informed choice for one or another method for the preparation of calibration gas mixtures. It also describes how these methods can be linked to national measurement standards to establish metrological traceability for the composition of the prepared gas mixtures. Since all techniques are dynamic and rely on flow rates, this document describes the calibration process by measurement of each individual flow rate generated by the device. Methods are also provided for assessing the composition of the generated gas mixtures by comparison with an already validated calibration gas mixture. This document provides general requirements for the use and operation of dynamic methods for gas mixture preparation. It also includes the necessary expressions for calculating the calibration gas composition and its associated uncertainty. Gas mixtures obtained by these dynamic methods can be used to calibrate or control gas analysers. The storage of dynamically prepared gas mixtures into bags or cylinders is beyond the scope of this document.

This document establishes the requirements for the purity analysis of materials used in the preparation of calibration gas mixtures and the use of these purity data in calculating the composition of the mixture thus prepared.

This document specifies the validation protocol of analytical methods used for ensuring the quality of the gaseous hydrogen (H2) at hydrogen distribution bases and hydrogen fuelling stations for road vehicles using proton exchange membrane (PEM) fuel cells. It also gives recommendations on the calculation of an uncertainty budget for the amount fraction. This document is established mainly for analysis done in laboratories after the sampling of hydrogen either at hydrogen distribution bases or at hydrogen refuelling stations. The specific requirements for on-line monitoring are not covered by this document. This document gives a list of suitable analytical techniques used to measure each impurity in hydrogen, according to the specification of hydrogen grade D defined by ISO 14687:—[1]. Moreover, recommendations for keeping the integrity of the sample are also given in order to ensure the quality of the measurement. It also includes the requirements for reporting the analytical results. [1] Under preparation. Stage at the time of publication: ISO/DIS 14687:2018.

ISO 6145 is a series of documents dealing with various dynamic methods used for the preparation of calibration gas mixtures. This document specifies a method for continuous preparation of calibration gas mixtures, from nominally pure gases or gas mixtures by use of thermal mass-flow controllers. The method is applicable to preparation of mixtures of non-reacting species, i.e. those which do not react with any material of construction of the flow path in the thermal mass-flow controller or the ancillary equipment. If this method is employed for preparation of calibration gas mixtures the optimum performance is as follows: the relative expanded measurement uncertainty U, obtained by multiplying the standard uncertainty by a coverage factor k = 2, is not greater than 2 %. If pre-mixed gases are used instead of pure gases, mole fractions below 10−6 can be obtained. The measurement of mass flow is not absolute and the flow controller requires independent calibration. The merits of the method are that a large quantity of the calibration gas mixture can be prepared on a continuous basis and that multi-component mixtures can be prepared as readily as binary mixtures if the appropriate number of thermal mass-flow controllers is utilized. NOTE Gas blending systems, based upon thermal mass-flow controllers, and some including the facility of computerization and automatic control, are commercially available.

This document provides requirements and guidelines on the necessary quality assurance required to produce calibration gas mixtures that are demonstrably stable and comparable. It shows that this is achieved by demonstrating that the composition of the calibration gas mixture is metrologically traceable to the SI. This document shows that calibration gas mixtures can be prepared according to methods that have measurements that are completely described in SI units. It describes procedures for verifying that the composition of such gas mixtures is correct within the stated measurement uncertainty. Guidance is given as to how to conduct the evaluation of uncertainty in these procedures. This document also shows how a calibration gas mixture with unknown composition can be calibrated by reference to traceable standard gas mixtures. This document covers the commonalities and differences of quality management schemes in use by producers of calibration gas mixtures, most notably those described in ISO/IEC 17025 and ISO 17034. These systems lead to gas mixtures with different characteristics, and this document explains these differences and their implications. Calibration gas mixtures, as prepared and certified for composition in accordance with this document, are used for the calibration of equipment, the performance evaluation of methods, measurement procedures and equipment.

ISO 6145-6:2017 specifies a method for the dynamic preparation of calibration gas mixtures containing at least two gases (usually one of them is a complementary gas) from pure gases or gas pre-mixtures using critical flow orifices systems. The method applies principally to the preparation of mixtures of non-reactive gases that do not react with any of the materials forming the gas circuit inside the critical flow orifices system or auxiliary equipment. It has the merit of allowing multi-component mixtures to be prepared as readily as binary mixtures if an appropriate number of critical flow orifices are used. By selecting appropriate combinations of critical flow orifices, a dilution ratio of 1 × 104 is achievable. Although it is more particularly applicable to the preparation of gas mixtures at atmospheric pressure, the method also offers the possibility of preparing calibration gas mixtures at pressures greater than atmospheric. The upstream pressure will need to be at least two times higher than downstream pressure. The range of flow rates covered by this document extends from 1 ml/min to 10 l/min.

ISO 16664:2017 describes factors that may influence the composition of pure gases and homogeneous gas mixtures used for calibration purposes. This document only applies to gases or gas mixtures that are within the "utilization period". It provides the following guidelines for the handling and use of calibration gas mixtures: - storage of calibration gas cylinders; - calibration gas withdrawal from cylinders; - transfer of calibration gas from cylinders to the point of calibration. It also outlines a method of assessing the stability of a gas mixture, taking into account the gas composition uncertainty given on the certificate and the user's measurement uncertainty.

ISO 12963:2017 provides methods for - calibrating an instrument with one or two calibration gas mixtures, - determining the composition of a gas sample, and - evaluating the uncertainty of the composition of the gas sample in relation to the uncertainty of the composition of the calibration gases used and the contribution of the measurement process. ISO 12963:2017 sets requirements to, and acceptance criteria for, the utilization of different measurement calibration designs with a limited (i.e. minimum) number of calibration gas mixtures used in calibration. The methods in this document are described for amount-of-substance fractions, but are also applicable for other composition quantities (such as mass fractions, volume fractions or concentrations).

ISO 6142-1:2015 specifies a gravimetric method for the preparation of calibration gas mixtures in cylinders with traceable values for the amount-of-substance fraction (amount fraction) of one or more components. This part of ISO 6142 describes a method for calculating the uncertainty associated with the amount fraction of each component. This uncertainty calculation requires the evaluation of the contributions to the uncertainty due to factors including the weighing process, the purity of the components, the stability of the mixture, and the verification of the final mixture. ISO 6142-1:2015 is only applicable to mixtures of gaseous or totally vaporized components, which may be introduced into the cylinder in the gaseous or liquid state. Both binary and multi-component gas mixtures (including natural-gas type mixtures) are covered by this part of ISO 6142. Methods for the batch production of more than one mixture in a single process are not included in this part of ISO 6142. ISO 6142-1:2015 requires estimation of the stability of the mixture for its intended life time (maximum storage life), but it is not for use with components that react with each other unintentionally. This part of ISO 6142 also requires the impurities in each parent gas or liquid used in the preparation of the mixture to be assessed and quantified.

ISO 7504:2015 defines terms related to gas analysis, with the main focus on terms related to calibration gas mixtures for use in gas analysis and gas measurements. It does not cover terms which relate only to specific applications.

ISO 6141:2015 specifies minimum requirements for the contents of certificates for homogeneous gas mixtures in gas cylinders to be used as calibration gas mixtures. Pure gases, when used as calibration gas mixtures, are also covered by this International Standard. Gases and gas mixtures produced for other purposes are not considered. The requirements in ISO 6141:2015 deal with the metrological aspects of calibration gas mixtures. Other aspects, such as safety and legislative aspects, are not covered. Furthermore, it specifies additional information (optional data) recommended for describing a homogeneous gas mixture, supplied under pressure in a cylinder or other container. It does not cover the field of safety-relevant data and related labelling.

ISO 6145 comprises a series of International Standards dealing with various dynamic methods used for the preparation of calibration gas mixtures. ISO 6145-2:2014 describes a method and preparation system using piston pumps. The mixture composition and its associated uncertainty are based on calibration of the piston pumps by dimensional measurements. The calibration gas mixtures prepared using this method consist of two or more components, prepared from pure gases or other gas mixtures using gas-mixing pumps. Such gas-mixing pumps contain at least two piston pumps, each driven with a defined ratio of strokes, and appropriate accessories for gas feeding and mixture homogenization. ISO 6145-2:2014 is applicable only to mixtures of gaseous or totally vaporized components including corrosive gases, as long as these components neither react with each other nor with the wetted surfaces of the mixing pump. The use of gas mixtures as parent gases is covered as well. Multi-component gas mixtures and multi-step dilution procedures are included in this International Standard as they are considered to be special cases of the preparation of two-component mixtures. ISO 6145-2:2014 describes a method of preparing calibration gas mixtures whose composition is expressed in volume fractions. The necessary equations and associated uncertainty evaluation to express the gas composition in amount?of?substance fractions are given in Annex A. With this method, provided that sufficient quality assurance and control measures are taken, calibration gas mixtures can be prepared with a relative expanded uncertainty of 0,5 % (coverage factor k = 2) in the volume fraction. Numerical examples showing that under specified conditions smaller uncertainties are attainable are given in Annexes B through D. Using this method, dilution ratios of 1:10 000 can be achieved in discrete increments. Lower fractions (down to 1 × 10−8) can be achieved by multi-stage dilution or by the use of gas mixtures as input gases. Final mixture flow rates of 5 l/h to 500 l/h can be realized depending on the equipment used.

ISO 6145-5:2009 is one of a series of International Standards dealing with the various dynamic volumetric techniques used for the preparation of calibration gas mixtures. This part specifies a method for the continuous production of calibration gas mixtures from pure gases or gas mixtures using capillary calibration devices in single or multiple combinations (gas dividers). Single capillary systems can be used to provide gas mixtures where the minor component is in the range of volume fractions from 10-8 to 0,5. The relative expanded uncertainty of this technique is less than ±2 % (k = 2) relative. This application is used in industrial gas mixing panels for the production of specific gas atmospheres. Gas dividers can be used to divide gas mixtures prepared from gases or gas mixtures into controlled proportions by volume. These devices are capable of dilutions in the range of volume fractions from 0,000 5 to 0,9 of the primary gas concentration with a relative repeatability of better than 0,5 %. Traceability of the gas mixtures produced by a gas divider is achieved by comparison of a mixture with gas mixtures related to national or international gas standards. An example is given in Annex A.

ISO 6145-9:2009 is one of a series of International Standards dealing with various dynamic volumetric methods used for the preparation of calibration gas mixtures. This part specifies a method for continuous production of calibration gas mixtures containing one or more readily condensable components. A relative expanded uncertainty of measurement, U, obtained by multiplying the relative combined standard uncertainty by a coverage factor k = 2, of not greater than ±1 %, can be obtained using this method. Unlike the methods presented in the other parts of ISO 6145, the method described in this part does not require accurate measurement of flow rates since flow rates do not appear in the equations for calculation of the volume fraction. Readily condensable gases and vapours commonly become adsorbed on surfaces, and it is therefore difficult to prepare stable calibration gas mixtures of accurately known composition, containing such components, by means of static methods. In addition, these calibration gas mixtures cannot be maintained under a pressure near the saturation limit without the occurrence of condensation. The saturation method can be employed to prepare mixtures of this type.

In ISO/TS 29041:2008, the gravimetric mixture preparation as given in ISO 6142 is investigated for existing a priori influences, as well as correlations introduced by data processing. All calculations refer to an example which consists in the preparation of a synthetic natural gas of a target composition as follows: 1,4 mol % N2, 1,8 mol % CO2, 9,4 mol % ethane, 3,4 mol % propane, 1 mol % n-butane, and 83 mol % methane. All considerations given for this example concerning mixture feasibility, choice of preparation procedure, and weighing steps and sequences are the same as given in ISO 6142. This also applies to all estimates for basic uncertainty sources and the purity tables of the gases used for preparation.

ISO 6145-11:2005 specifies a method for the preparation of calibration gas mixtures by using electrochemical generation of a calibration component and introduction into a complementary gas flow. By alteration of the gas flow or the charge passed through the cell electrolyte, it is possible to change the composition of the gas mixture. The relative expanded uncertainty of the calibration gas content, U, obtained by multiplying the relative combined standard uncertainties by a coverage factor, k = 2, is not greater than 5 %. The method described in ISO 6145-11:2005 is intended to be applied to the preparation of calibration gas mixtures in the volume fraction ranges (0,1 to 250) x 10-6.

ISO 15796:2005 specifies generic methods for detecting and correcting bias (systematic errors) of analytical procedures for the analysis of gases, using reference gas mixtures or reference analytical procedures, as well as for estimating the correction uncertainty. The main sources of (and parameters affecting) bias of analytical procedures are instrumental drift (time) and matrix interferences (matrix composition). Moreover, bias normally varies with analyte concentration. ISO 15796:2005 therefore establishes protocols for detecting and correcting drift for an analytical system of limited stability, and for investigating and handling bias of a stable analytical system for a specified range of sample composition. These protocols are intended to be used in method development and method validation studies, either separately or sequentially. ISO 15796:2005 specifies procedures for two options, applicable to systematic effects, as follows: 1) tracing the observed pattern of deviations and correcting for their effect, 2) averaging over their effects and increasing the uncertainty, where normally the first option entails lower uncertainty at the expense of higher effort. For the convenience of the user, the methods specified in ISO 15796:2005 are described for procedures of composition analysis, i.e. procedures for measuring the concentration of a specified analyte in a gas mixture. However, they are equally applicable to measurements of physico-chemical properties of a gas or gas mixture relevant to gas analysis, and translation into this subject field is straightforward.

ISO 6145-8:2005 specifies a dynamic method using diffusion for the preparation of calibration gas mixtures containing component mole fractions ranging from 10-9 to 10-3. A relative expanded uncertainty of measurement, U, obtained by multiplying the relative combined standard uncertainty by a coverage factor k = 2, of not greater than ± 2 % can be achieved by using this method. By keeping the path between the diffusion source and place of use as short as possible, the method can be applied for the generation of low-concentration calibration gases of organic components that are liquid at room temperature, with boiling points ranging from about 40 °C to 160 °C. ISO 6145-8:2005 is applicable not only for the generation of calibration gas mixtures of a wide range of hydrocarbons at ambient and indoor air concentration levels, but also for the generation of low-concentration gas mixtures of water.

ISO 6145-4:2004 specifies a method for continuous production of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by continuous injection of the calibration component(s) into a complementary gas stream by means of a syringe. If pre-mixed gases are used instead of pure gases (see Annex A), much lower volume fractions can be obtained. The volume flow rates, from which the volume fractions are determined, can be calculated from the individual flow rates and can be independently measured by a suitable method given in ISO 6145-1. The merits of the method are that a substantial quantity of the gas mixture can be prepared on a continuous basis and that multi-component mixtures can be prepared almost as readily as binary mixtures if the appropriate number of syringes is utilized, or if the syringe already contains a multi-component mixture of known composition. This method also provides a convenient means for increasing the volume fraction of the calibration component in the mixture in small steps. It is therefore a useful method for evaluation of other characteristics of gas analysers, such as minimum detection limit and dead zone, as well as accuracy. The relative expanded uncertainty in the volume fraction obtainable for a binary mixture (at a coverage factor of 2) is 5 % and the range of applicability is 10-5 to 10-2.

ISO 14912:2003 defines the following quantities commonly used to express the composition of gas mixtures: mole fraction, mass fraction and volume fraction, as well as mole concentration, mass concentration and volume concentration. Relating to these quantities of composition, ISO 14912:2003 provides methods for the conversion between different quantities and the conversion between different state conditions. Conversion between different quantities means calculating the numerical value of an analyte content in terms of one of the quantities listed above from the numerical value of the same analyte content, at the same pressure and temperature of the gas mixture, given in terms of another of these quantities. Conversion between different state conditions means calculating the numerical value of an analyte content, in terms of one of the quantities listed above, under one set of state conditions from the numerical value of the same quantity under another set of state conditions, i.e. pressure and temperature, of the gas mixture. Gas mixture composition can be converted simultaneously between different quantities of composition and different state conditions by combination of the two types of conversion. ISO 14912:2003 is only applicable to homogeneous and stable gas mixtures. Therefore any state conditions (pressure and temperature) considered need to be well outside from the condensation region of the gas mixture and that of each of the specified analytes.

ISO 6144:2003 specifies a method for the preparation of calibration gas mixtures by a static volumetric method and provides a procedure for calculating the volumetric composition of the mixture. It can be used either with binary gas mixtures (containing one calibration component in a complementary gas, which is usually nitrogen or air) or with mixtures containing more than one component in the complementary gas. This International Standard also specifies how the expanded uncertainty in the volume fraction of each calibration component in the mixture is determined by a rigorous evaluation of all the measurement uncertainties involved, including those associated with the apparatus used for the preparation of the gas mixture and those associated with the experimental procedure itself.

This part of ISO 6145 specifies a dynamic method using permeation membranes for the preparation of calibration gas mixtures containing component mole fractions ranging from 10−9 and 10−6. A relative expanded uncertainty of 2,5 % of the component mole fraction can be achieved using this method. In the mole fraction range considered, it is difficult to maintain some gas mixtures, for example in cylinders, in a stable state. It is therefore desirable to prepare the calibration gas immediately before use, and to transfer it by the shortest possible path to the place where it is to be used. This technique has been successfully applied in generating low content calibration gas mixtures of, for example, sulfur dioxide (SO2), nitrogen dioxide (NO2) and benzene (C6H6) in air. If the carrier gas flow is measured as a gas mass-flow, the preparation of calibration gas mixtures using permeation tubes is a dynamic-gravimetric method which gives contents in mole fractions.

This International Standard provides methods for _ determining the composition of a calibration gas mixture by comparison with appropriate reference gas mixtures, _ calculating the uncertainty of the composition of a calibration gas mixture in relation to the known uncertainty of the composition of the reference gas mixtures with which it was compared, _ checking the composition attributed to a calibration gas mixture by comparison with appropriate reference gas mixtures, _ comparing the composition of several calibration gas mixtures, e.g. for the purpose of comparing different methods of gas mixture preparation, or for testing consistency among gas mixtures of closely related composition. NOTE In principle, the method described in this document is also applicable to the analysis of (largely) unknown samples instead of prospective calibration gas mixtures (i.e. gas mixtures which are intended for use as calibration gas mixtures). Such applications, however, require appropriate care and consideration of additional uncertainty components, for example concerning the effect of matrix differences between the reference gases used for calibration and the analysed sample.

ISO 19229:2015 sets requirements for the purity analysis of materials used in the preparation of calibration gas mixtures and the use of these data in calculating the composition of the mixture thus prepared.

ISO 6145-7:2009 specifies a method for continuous production of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by use of commercially available thermal mass-flow controllers. If this method is employed for the preparation of calibration gas mixtures, the optimum performance is as follows: the relative expanded uncertainty of measurement, U, obtained by multiplying the combined standard uncertainty by a coverage factor k = 2, is not greater than 2 %. If pre-mixed gases are used instead of pure gases, mole fractions below 10-6 can be obtained. The measurement of mass flow is not absolute and the flow controller requires independent calibration. The merits of the method are that a large quantity of the gas mixture can be prepared on a continuous basis and that multicomponent mixtures can be prepared as readily as binary mixtures if the appropriate number of thermal mass-flow controllers is utilized.

ISO 16664:2004 describes factors that may influence the composition of pure gases and homogeneous gas mixtures used for calibration purposes. ISO 16664:2004 only applies to gases or gas mixtures that are within the "utilization period", and it pays special attention to storage of calibration gas cylinders; calibration gas withdrawal from cylinders; transfer of calibration gas from cylinders to the point of calibration. ISO 16664:2004 also outlines a method of assessing the stability for a gas mixture, and takes into account the gas composition uncertainty given on the certificate and the users measurement uncertainty.

ISO 6145-1:2003 specifies the calibration methods involved in the preparation of gas mixtures by dynamic volumetric techniques. It also gives a brief presentation of a non-exhaustive list of examples of dynamic volumetric techniques which are described in more detail in other parts of ISO 6145.

ISO 6145-6:2003 specifies a method for the continuous production of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by use of critical orifice systems. By selection of appropriate combinations of orifices and with the use of pure gases, the volume fraction of the calibration component in the calibration gas mixture can be varied by a factor of 104. Additionally, it can be changed by a factor of 102 by changing the initial pressures in the orifice systems. The uncertainty of the method depends mainly upon the flow calibration method and the variations in temperature and outlet pressure. The relative expanded uncertainty in the volume fraction obtainable for a binary mixture (at a coverage factor of 2) is 3 %. If pre-mixed gases are used instead of pure gases, much lower volume fractions can be obtained. The mass flow rates or volume flow rates, from which the mass or volume fractions are determined, can be calculated and can be independently measured by a suitable method given in ISO 6145-1. The merits of the method are that multi-component mixtures can be prepared as readily as binary mixtures if the appropriate number of orifices is utilized, and that a large quantity of calibration gas mixture can be prepared on a continuous basis. The range of flow rates can be from several millilitres per minute to approximately 10 l/min. Although particularly applicable to preparation of gas mixtures at barometric pressure, the method also provides a means of preparation of calibration gas mixtures at pressures above barometric pressure.

ISO/TS 14167:2003 provides guidance on the quality aspects in the field of gas analysis that are implemented in order to achieve a result with a valid measurement uncertainty. It provides guidelines on quality aspects to be employed in gas analysis using calibration gas mixtures and their subsequent validation and/or verification, and the testing of the analytical performance of gas analysis instruments. These guidelines have the overall objective of defining procedures which will ensure that measurements of gas composition are reliable, comparable and consistent between different organizations and countries. It explains, in particular, the concepts of measurement uncertainty and of traceability as effective quality assurance tools for defining the measurement uncertainty of particular measurement results. It also gives guidance on how to identify and estimate measurement uncertainty components of the result, and how to combine these uncertainty components in order to obtain the overall uncertainty.

Describes the method using mixtures with one or more component(s), with a volume radio equal to or greater than 0,1 %, the repeatability of which on the concentration of each of the components is approximalety 0,5 % in relative value.

Describes the preparation of mixtures by continuos mixing of volume flows, whereby the precision of the concentration of each constituent in the range from 10 000 to 10 ppm (V/V) amounts to about 5%. Includes a practical example with figure.

Describes various methods and given a brief and non-exhaustivepresentation of examples of techniques and error calculations which are described in more detail in other parts of ISO 6145. Tabulates examples of influence of temperature and pressure variations. Seven figures illustrate different equipment.

Defines terms relating to gas analysis, in English and in French. The vocabulary is restricted to the presentation of the methods most currently used in gas analysis. Alphabetical indexes in english and french languages are also given.