American Journal of Research Communication www.usa-journals.com El-Naggar, 2013: Vol 1 (3) ajrc.journal@gmail.com 219 Factors affecting selection of mobile phase in gas Chromatography A.Y. El-Naggar 1, 2 1- Egyptian Petroleum Research Institute, Nasr City, Cairo, Egypt 2- Chemistry Department, Faculty of Science, Taif University, KSA Abstract Selection of mobile phases markedly affect separation efficiency of eluted probes in gas chromatography (GC), the mobile phases have a pronounced effect on the retention times and efficiency of natural gas separation. In solid chromatography, carrier gases which are adsorbed to any extent occupy more active adsorption sites, reducing the net heat of adsorption of the eluted zone. The efficiency of separation of a light hydrocarbon mixture is shown to depend markedly on the type and pressure of mobile phase in addition to the column temperatures. Hydrogen and helium are the preferred mobile phases in GSC giving higher efficiency of separation because of their higher thermal conductivity. Helium is the best one because of its safety to handle than hydrogen. Nitrogen is the preferred mobile phase used in FID giving high efficiency of heavy components of natural gas separation. Keywords: Mobile phases, Retention Times, separation efficiency and gas chromatography {Citation: A.Y. El-Naggar. Factors affecting selection of mobile phase in gas Chromatography. American Journal of Research Communication, 2013, 1(3): 219-228} www.usa-journals.com , ISSN: 2325-4076. Introduction The main goal of gas chromatography is separation of multi-component mixtures, to achieve high efficiency of separation, one usually has to optimize the separation process by varying stationary phase, carrier gas flow, column temperature, etc. (1-3) The opinion of many chromatographers about the role of carrier gas is limited only to transporting analyzed compounds along the column. However, carrier gas dramatically affects relative retention values. Various carrier gases have been used in gas liquid chromatography (GLC) and gas solid chromatography (GSC). Nitrogen, helium, hydrogen, and carbon dioxide have been reported to give good results as far as detector stability and sensitivity are concerned (4) . The use of different carrier gases has