The operation conditions have a great influence on chromatographic separation.

Column length and column inner diameter: Generally, if the length of column is increased, the separation ability can be improved accordingly. Smaller column inner diameter, better separation performance. Larger column innder diameter, greater processing capacity. However, if the column inner diameter is too large, the carrier could not be spreaded evenly in chromatographic column. Generally, the inner diameter of analytical column is 3mm to 6mm, the column length is 1m to 4m.

Column temperature: This is an important operating variable, and directly affects separation ability and analysis speed. The basis of selection of column temperature is boiling point range of mixtures, stationary liquid ratio and sensitivity of calibrator. Increasing column temperature can shorten analysis time; decreasing column temperature can enlarge selection range of chromatographic columns, which is good for separating of compounds and improving stability of chromatographic column and extending column life. Generally, it is suggested to adopt the column temperature which is equal to or dozens of degrees higher than the average boiling point of sample. Use low column temperature for easy volatile sample; and use high column temperature for less volatile sample.

Carrier gas flow rate: This is one of important reasons for deciding chromatographic separation. Generally speaking, higher flow rate, narrower chromatographic peak, on the contrary, the chromatographic peak is wider. However, too high or too low flow rate is not good for separation. The flow rate should be steady, usually the flow rate range is 10mL to 100mL per minute.

Stationary phase: It consists of solid adsorbent or carrier coating with fixative liquid.
(1) Solid adsorbent or carrier size: Usually adopt 40 - 60 mesh, 60 - 80 mesh and 80 - 100 mesh. When use the same length column, the separation efficiency of thin particles is better than thick ones.
(2) Fixative liquid content: It has a great influence on separation efficiency. Generally, the ratio of fixative liquid content to carrier content is 15% to 25%. Too large ratio is bad for separation, and too small ratio will cause tailing peak.

Sample injection: Generally, fast injection, small sample quantity and high injection temperature make good separation. For injection liquid sample, the speed should be quick, vaporization temperature should be higher than the boiling point value of high boiling point compound of sample. One time vaporization ensures the non-broadening of chromatogaphic peak shape and high column efficiency. When the sample volume reaches a certain limit, the full width at half maxima (FWHM) is not changed. If the sample volume is too much, it will cause the overload of chromatographic column. Generally, if the column length is increased 4 times, the sample quantity is increased 1 time. For routine analysis, the volume of liquid sample injection is 1 microlitre to 20 microlitres; the volume of gas sample injection is 0.1mL to 5mL.