Gas cromatography

Chromatographic methods

One of the analytical techniques that has seen the most significant advances in recent years is chromatography, thanks to its ability to separate the components of a mixture.

To meet the demands of increasingly sophisticated chromatographs, Nippon Gases offers a wide range of high-purity gases and high-precision mixtures, prepared using technologically advanced processes to ensure effective control of contaminants.

Four different types of speciality gases are required for gas chromatography analysis:

  • Carrier gas
  • Auxiliary gases
  • Support gases
  • Purge gases

Gas chromatography is an instrumental technique in which the sample is nebulised and injected at the top of a chromatographic column. Elution occurs through the flow of an inert gas mobile phase, resulting in the separation of gaseous species based on their differing affinities for the stationary phase of which the chromatographic column is composed.

Carrier gas

In gas chromatography, the carrier gas acts as the mobile phase, i.e. the eluent gas that flows through the column, carrying the various components of the sample with it. It is essential that the carrier gas is pure in order to avoid secondary reactions that would produce undesirable effects.

Auxiliary gases

Auxiliary gases do not directly participate in the separation process, but are essential for the proper functioning of the analysers. For example, in a flame ionisation detector using hydrogen as fuel, the presence of any contaminants could contribute to increased background noise, thereby limiting the instrument’s sensitivity.

Carrier gas

In certain specific cases where a high gas flow rate is required, the carrier gas must be supplemented with another gas. For example, in a high-resolution gas chromatograph with an electron capture detector, nitrogen and/or an argon-methane mixture act as carrier gases.

Purge gas

With some liquid chromatography instruments, a gas is required to remove dissolved gases (typically oxygen and nitrogen), which, if not eliminated, reduce separation efficiency in the column, causing peak broadening and interfering with detector operation. Purge gas is also used, amongst other things, in dynamic and static ‘headspace’ systems and in thermal desorption, such as in gas chromatography peripherals.

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