The preparation of standard gas and application

The concept of a standard gas understanding 1. Definition: The standard gas is one or more of the exact nature of magnitude with the certificate has metrological traceability, the gas calibration of the instrument, or to evaluate the measurement method for the assignment of two substances. Features: (1) Stability: Under the provisions of the interval and environmental conditions, the characteristics of the magnitude of the standard gas is kept within the limits prescribed performance standards stability characteristics of gas cylinders and valves in gas adsorption and does not produce reaction, no chemical reaction between the gas component (2) Uniformity: Uniformity is a state of one or more characteristics of a substance having the same component or the same uniformity of the performance of a gas at standard temperature and pressure. Under the characteristic values of the components within the provisions of the gas component is not hierarchical, non-liquefied (3) Accuracy:..... refers to the standard value of the standard gas with a precise measurement of its magnitude can be traced back two standard preparation of gas: either by pressure method, volume method or standard weighing prepared bottled gas, are required to achieve the following process of filling analytical testing ---- ---- ---- Rolling mix given. value (or standard material test report certificate) by the pressure method / volume method or weighing method to achieve a mixed gas filling is no longer a problem, as long as the pressure gauge with accuracy and precision balance. filling is easy . realized how accurate and effective standard gas money, is the task of all standard gas manufacturers and research institutions are facing the impact of three standard gas values stability factors: 1. cylinder and valve materials before the gas filling, To fully take into account the various components of the gas cylinder materials, valves and sealing materials compatibility, as a standard gas containers, steel, aluminum alloy materials have been widely used. Different concentrations of the different components is standard gas and the cylinder valve material or compatible materials, direct impact on the quality standards of gas such as hydrogen fluoride, hydrogen chloride, fluorine, chlorine, methyl chloride, ethyl chloride, methyl bromide reacts with the aluminum, etc., can not be directly used to contain aluminum cylinders. certain concentration of corrosive gases can not choose copper valves need to choose stainless steel valves. 2. A method for handling gas cylinders containing standard gas cylinders, the inner surface of the need for regular and special deals, in order to ensure the stability of a standard gas money. processing method includes heating remove moisture inside the cylinder, vacuum to remove air and other impurities replacement gas, coating the inner surface of the inner cylinder surface reduces physical adsorption or chemical reaction with the component gases; the inner surface of the inner cylinder passivation Good inert surface, the magnitude of the inert gas is conducive to the stability of the mixture. For trace inert gases, the correct choice of the standard cylinder is the key to the gas processing method preparation. 3. The composition of the purity of the feed gas and the components mixed gas impurities. In addition to material compatibility and proper handling of cylinders, the purity of the raw materials is another noteworthy problem. If the raw materials and the preparation containing the same impurity components, accurate quantification of impurities directly affects the component 1ppm CO standard gas values such as the preparation of nitrogen gas as the background, in addition to know the purity of the components of the gas, but also know that high purity nitrogen content of CO2 in this way in order to give an accurate measure of CO2. The gas group Compatibility points if formulated nitrogen NO / N2 standard gas, if high purity nitrogen containing oxygen or oxygen into the filling in, then it becomes a mixed gas NO2 / N2 similar problem can be summarized in the following aspects: (1) acid gases and alkaline gases: Common acidic gases include: HCl, H2S, SO, NO2, organic acids and alkaline gases can not be an organic amine such as NH3 and filled into a gas cylinder; (2) a reducing gas and oxidizing gas incompatible and can not be filled in a gas cylinder as:. H2S and SO2, H2S and NO2, H2 and CL2, etc. (3) or the spontaneous combustion of combustible gas and oxidizing gases: If the lower explosion limit or above The minimum oxygen demand over the combustible gas and oxidizing gas cylinders filled with a danger of explosion. hydrocarbons and hydrogen easily be thought of as combustible gases, carbon monoxide and combustible but often overlooked, The only concern its toxicity. Oxygen is combustion-supporting gas, and NO, N2O NO2, F2, CL2, NF3, and other oxidizing gases can also combustion, and the combustible gas explosions and reaction. When preparing a combustible gas and an oxidizing When the gas is mixed gas concentration and preparation to include the preparation of pressure through rigorous calculation; four test standard gas Not only that, but also to develop a rigorous preparation process including injection sequence, and mix during the preparation and analysis: Standard gas. The magnitude meets the requirements, analysis and detection is one of the important part. According to the preparation method after filling is complete, how uniformity, stability and accuracy values, it is necessary to complete the analysis and detection by gas chromatography is widely used as a The quantitative analysis method has been recognized, the separation column from the development of capillary columns packed column, greatly improving the efficiency of the column, and detection technology from developed to detect trace constant and trace analysis commonly used detectors include TCD, FID, . ECD, FPD, TSD, HID, DID, PDID chemical analysis method is also used as a classic analysis of corrosive gases in the analysis, infrared spectroscopy, visible - UV spectroscopy, chromatography / mass spectrometry technique is also used in gas analysis In V. Application of the standard gas. how to better use the standard gas is an issue of concern to the standard gas manufacturer, usually in the preparation of certain trace gases or corrosive standard trace oxygen, nitrogen standard gas, the preparation process can be described as full of the blood and tears, and for customers, often due to improper use, causing some false results should be done using the standard gas following points: (1) Select the regulator and gas pipeline route, be sure to pay attention to materials and compatible gas, such as doing a trace of oxygen, nitrogen standard gas piping can not select a plastic tube and the rubber tubing and to select a metal pipe, and as corrosive gases, the choice of metal tubing Untreated adsorption of components produced; (2) Storage cylinders at a suitable temperature, for easy liquefied gases, to pay attention to the storage temperature and the use temperature, are easily avoided at low temperature liquefied gas component; front (3) sampling, pressure Mediators and piping systems fully cleaned, ensure consistent sampling and sample cylinders parts group concentration; (4) the standard gas sampling is complete, the cylinder valve to shut Bi, counter-proliferation to avoid air cylinders; (5) Note Validity and minimum standards allow the use of gas pressure.