How is the standard gas prepared

Release time:2023-03-29

Standard gas preparation method

The methods of preparing low concentration standard gas with raw gas include static and dynamic distribution.

(1) Static valve distribution method

Static gas distribution method is to add a certain amount of gaseous or vapor state of raw gas into the known volume of the container, and then filled with diluted gas, mixed. The concentration of standard gas is calculated from the addition of raw gas and dilution gas and the volume of the container. The advantage of this gas distribution method is that the equipment is simple and the operation is easy. However, due to the active chemical properties of some gases, chemical reactions may occur after contact with the container wall for a long time. At the same time, the container wall also has adsorption effect, so the concentration of gas preparation is not accurate or its concentration changes with the placement time, especially the preparation of low concentration standard gas, often cause large errors. It is simple to prepare standard gas with poor activity and small dosage.

Commonly used static distribution methods include syringe distribution, cylinder distribution, plastic bag distribution and high-pressure cylinder distribution, etc.

1. Syringe Air distribution method

When a small amount of standard gas is prepared, raw gas is absorbed with a 100mL syringe and diluted several times. For example, take 10mL of CO gas of 99.99% purity with a 100mL syringe, dilute it to 100mL with purified air, shake the PTFE sheet in the syringe to make it evenly mixed, then discharge 90mL, and dilute the remaining 10mL mixture with purified air to 100mL, and so on for six consecutive times. Finally, the standard gas with CO concentration of 1ppm was obtained.

keyword: How is the standard gas prepared