Gas-pak

This is a method used in production of an anaerobic environment. This method of "anaerorbiosis" as others is used to culture bacteria which die or fail to grow in presence of oxygen ("anaerobes"). It is a much simpler technique than the McIntosh and Filde's anaerobic jar where one need to pump gases in and out.

There are commercially available, use-and-throw sachets containing a dry powder or pellets, which when mixed with water and kept in an appropriately sized airtight jar, produces and atmosphere free of elemental oxygen gas. These are used to produce an anaerobic cultures in Microbiology. [Textbook of Microbiology by Prof. C P Baveja, ISBN 81-7855-266-3] [extbook of Microbiology by Ananthanarayan and Panikar, ISBN 81-250-2808-0]

Constituents of gas-pak sachets

#Sodium borohydride - NaBH₄
#Sodium bicarbonate - NaHCO₃
#Citric acid - C₃H₅O(COOH)₃
#Cobalt chloride - CoCl₂ (catalyst)
....add water(H₂O) to activate.

Reactions

*NaBH₄ + 2 H₂O = NaBO₂ + 4 H₂↑
*C₃H₅O(COOH)₃ + 2 NaHCO₃ + [CoCl₂] = C₃H₅O(COONa)₃ + 3 CO₂ + 3 H₂ + [CoCl₂]
*2 H₂ + O₂ + [Catalyst] = 2 H₂O + [Catalyst]

Consumption of oxygen

These chemicals react with water to produce hydrogen and carbon dioxide along with sodium citrate and water (C₃H₅O(COONa)₃) as byproducts [http://en.wiktionary.org/wiki/byproduct] . Again, Hydrogen, in presence of oxygen and a catalyst like Palladiumised alumina(supplied separately), combines to form water.

Culture method

In an air-tight gas jar the culture media, the gas-pak sachet (opened and water added) and an indicator are placed. The jar is incubated at the desired temperature. The indicator tells whether the environment was indeed oxygen free or not.

Indicator: Generally used chemical indicator for this purpose is "chemical methylene blue solution" that has never since synthesis been exposed to elemental oxygen. It is colorless and gets colored deep blue on oxidation in presence of atmospheric oxygen in the jar.

References