Gas analysis

A general term for chemical analysis of gaseous substances. There are methods for qualitatively and quantitatively analyzing gases using various chemical and physical properties such as color, odor, reactivity, flammability, adsorptivity, and absorption. The following methods are commonly known:

[1] Absorption method: (1) The absorption volume method, in which a mixed gas sample is treated with a suitable gas absorbent to selectively absorb only certain components and the component content is determined from the volumetric absorption loss, and (2) the absorption weight method, in which a sample gas is absorbed into an absorbent whose weight has been measured in advance and the amount of moisture and carbon dioxide is determined from the increase in weight. For example, this method involves passing a gas containing water vapor through a desiccant such as magnesium perchlorate, or passing a gas containing carbon dioxide through an absorbent such as soda asbestos, and quantifying the amount of moisture and carbon dioxide as the weight increase.

[2] Combustion method: This method involves adding oxygen or other substances to a combustible sample to cause a combustion reaction, and quantifying the amount of the substance from the volume change that occurs during the reaction. It is widely used to quantify hydrogen, oxygen, hydrocarbons, and nitrogen oxides.

[3] Titration and colorimetry: Titration involves passing a fixed amount of gas sample through an absorbing liquid, titrating the absorbing liquid, and determining the content of the sample components from the titration amount. Colorimetry involves measuring the color developed by the absorbing liquid colorimetrically.

[4] Test strip method and detector tube method These are variations of the colorimetric method. The test strip method observes the discoloration of test strip soaked in a color-developing reagent, while the detector tube method observes the discoloration caused by the passage of a sample gas through a thin glass tube filled with silica gel or the like that has absorbed a color-developing reagent. Both methods have the advantage of being able to easily and quickly detect and semi-quantify trace components.

[5] Gas chromatography: A method of separating and analyzing substances by utilizing the adsorption or distribution power of substances between a gas and a solid or liquid in contact with it.

[6] Physical methods: Methods for measuring and quantifying density, viscosity, thermal conductivity, heat of reaction, electrical, magnetic and optical properties, etc.

In addition to the above, gas volumetric analysis, in which gas generated during a chemical reaction is collected in a graduated tube and its volume is measured, and the manometer method are also generally referred to as gas analysis.

[Takada Takeo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

気体状態の物質に対して行う化学分析の総称。気体の色、におい、反応性、燃焼性、吸着性、吸収性その他の種々の化学的、物理的性質を利用して気体の定性、定量を行う方法があり、一般に次のような方法が知られている。

〔1〕吸収法　(1)混合気体試料を適当な気体吸収剤で処理して、ある成分だけを選択的に吸収させ容積の吸収減量から成分含有量を知る吸収容積法と、(2)あらかじめ重量を測定しておいた吸収剤に試料気体を吸収させ、その増量から求める吸収重量法とがある。たとえば、水蒸気を含む気体を過塩素酸マグネシウムなどの乾燥剤に通したり、二酸化炭素を含む気体をソーダアスベストのような吸収剤に通して、その重量増加分として水分と二酸化炭素を定量する方法がこれにあたる。

〔2〕燃焼法　可燃性試料に酸素その他を加えて燃焼反応をおこさせ、その際おこる体積変化などから定量する方法である。水素、酸素、炭化水素、窒素酸化物の定量などに広く用いられている。

〔3〕滴定法、比色法　気体試料の一定量を吸収液に通じ、吸収液を滴定し、その滴定量から試料成分の含有量を求めるのが滴定法、吸収液による発色を比色定量するのが比色法である。

〔4〕試験紙法、検知管法　比色法の変形で、試験紙法は発色試薬をしみ込ませた試験紙の変色を、検知管法は発色試薬を吸着させたシリカゲルなどを細いガラス管に詰め、試料気体の通過によるその変色を見る方法で、両者とも微量成分の検出や半定量が簡便迅速に行える点に特長がある。

〔5〕ガスクロマトグラフィー　気体中と、それに接している固体または液体中との間における物質の吸着または分配力を利用して、物質の分離や分析を行う方法。

〔6〕物理的諸方法　密度、粘度、熱伝導度、反応熱、電気的・磁気的・光学的性質などを測定して定量する方法。

　以上のほか、化学反応に伴って発生するガスを目盛り管に集めてその体積を測定するガス容量分析や、検圧計法をも含めて一般にガス分析とよぶこともある。

［高田健夫］

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