Most separation works are carried out at room temperature. If laboratory temperature keeps the same, the separation work goes smoothly. However, in most cases, the temperature will change, which directly affects the experiments. Temperature affects the isocratic retention time of separation. Generally, for every increasing of temperature, the retention time is reduced by 1% - 3%. Even the temperature is under controlled, however, due to the temperature difference between day and night, there is great change in room temperature, especially analyzing a large quantity of samples, the retention time will be different tremendous. Comparing to isocratic elution, the retention time of gradient elution is not sensitive to the change of temperature.

Change of temperature will cause the change of material which separated by chromatographic column. This change depends on nature of compound. So this kinds of compound can be separated by controlled temperature. If the temperature of chromatographic column is not balanced well, it will cause broadening of peak. If column temperature, retention time and column selectivity changed, the width of peak will change accordingly. Rising of column temperature will enlarge number of theoretical plates, narrow peak and improve sensitivity. If chromatographic column, solvent bottle, pump and automatic sampler are worked at room temperature, the temperature of whole system is the same. If heat chromatographic column only, solvent and other parts of system are still worked at room temperature, the temperature of chromatographic column inlet will be lower than outlet's, this kind of temperature is negative to peak shape. One of the solutions is that increase a pre-heater between automatic sampler and chromatographic column. (At present, column boxes of some suppliers are equipped pre-heaters.) Thus, the reason of broadening of peak width and tailing of peak could be explained. The front line temperature of chromatographic belt is higher than rear line's, so it moves faster. Then, the peak width broadening and tailing peak are appeared. Now, pre-heater is commonly applied to improve peak shape.