Gas composition test in buffer package

Because of different packaging products, such as packaging with volatile products, or different packaging techniques, such as various inflatable packaging, it is often necessary to understand the gas composition and content of the package. For this type of test, a gas analyzer is often used, which uses the flow out of the column to present a chromatographic peak with a certain separation distance on the chromatogram. This is the basis for qualitative and quantitative analysis of the gas to be measured.

Gas chromatograph is superior to thermal conductivity gas analyzer and infrared gas analyzer in the analysis of gas composition and content. Its high selectivity, high sensitivity, and high speed are unmatched by these two analyzers. . Differences between certain properties of different gases, and these differences are converted into electrical signals, and the instrument displays the test parameters of the measured gas. There are two types of instruments commonly used in testing:

(1) Thermal conductivity gas analyzers,

Thermal conductivity gas analyzer is one of the earliest applied analytical instruments. It can test the percentage content of each component in the mixed gas. Any object has a thermal conductivity. This ability is expressed in terms of thermal conductivity. Different objects have different thermal conductivities, and gas is the same. This is the basic point at which the instrument distinguishes different gas contents. For a single gas, the type of gas can be determined based on the measured thermal conductivity. For multi-component mixed gases that do not interact with each other, the thermal conductivity can be approximately considered as the arithmetic mean of the thermal conductivity of each component. Changes in the content of a certain component will inevitably cause changes in the thermal conductivity of the mixed gas. . In this way, the percentage content of the desired component can be determined by measuring the change in the thermal conductivity of the mixed gas.

However, if you want to use the principle of thermal conductivity to analyze the content of a certain component in a mixed gas, the thermal conductivity of the mixed gas should only change with the content of the component to be measured. Therefore, the requirements for mixed gases are: In addition to the components to be measured in the mixed gas, the thermal conductivity of the remaining components must be the same or similar; the thermal conductivity of the tested components must be significantly different from the thermal conductivity of the remaining components. The greater the difference, the easier it is to test.

There are many types of thermal conductivity gas analyzers. A certain type of instrument can only be used to test the percentage of a certain gas. Before the test, the mixed gas to be tested is generally subjected to pretreatment, that is, menstrual blood filtration and drying.

(2) Infrared gas analyzer

This kind of instrument has high sensitivity and good selectivity. It not only can analyze the gas in the package, but also can detect the gas permeability of the package material. Wide application in gas analysis.

Infrared is an electromagnetic wave, and various gas molecules have a certain absorption ability for infrared rays, but it is not in the entire frequency range of the infrared band, it can only absorb infrared rays in some bands. These bands are called feature absorption bands. Different gases have different absorption bands. If infrared rays pass through a mixed gas and there is a lack of infrared absorption in a specific absorption band, it can be concluded that the gas contains certain gas components.

In addition, infrared rays also have a thermal effect. When infrared rays act on the gas, the gas absorbs the radiant energy of the infrared rays to increase the temperature of the gas. Using this conversion relationship, one can determine how much the gas absorbs infrared radiation energy and thus determine the amount of a gas in it. The detectors in various infrared analyzers almost all use this feature.

The infrared gas analyzer mainly uses the spectrum between 1 and 25/μm, but the characteristic absorption band of the gas composed of the same atoms is not within this spectrum, so the instrument cannot analyze such gases. This kind of instrument can be divided into direct reading type and compensation type according to the signal detection system. The former has the characteristics of high sensitivity, simple structure, fast response speed, testable trace gas, and is the main species currently used in China.

(3) Gas chromatograph

Gas chromatograph is a multi-component analyzer, which has the characteristics of high sensitivity, good selectivity, fast analysis speed and wide application range. The instrument uses a treated gaseous substance, also called a carrier gas, to carry the gas to be analyzed into the column. After the gas mixture passes through the column, it is separated into a single component, which in turn enters the detector. The time of composition entry and its content are recorded by the recorder. The recorded outflow curve is called the chromatogram. According to the chromatogram, the gas to be measured can be qualitatively and quantitatively analyzed to obtain the name and content of each component. Because each component flows out of the column at different times and flow rates, a chromatographic peak with a certain separation distance appears on the chromatogram. This is the basis for the qualitative and quantitative analysis of the gas to be measured.

Gas chromatograph is superior to thermal conductivity gas analyzer and infrared gas analyzer in the analysis of gas composition and content. Its high selectivity, high sensitivity, and high speed are unmatched by these two analyzers. .

Excerpt from: Flying Waves