Trace analysis is popular in food, environmental and biological sample.For the high resolution and especially suitable for polar, unvolatile and thermal unstable compounds, high performance liquid chromatography (HPLC) based techniques are preferred to analyze more than 70% chemicals.Solid phase extraction (SPE) is the most effective and convenient sample pretreatment method in trace analysis until now.However, offiine SPE is usually laborious and time consuming.As an alternative method, online SPE-LC has been developed to improve the sensitivity with a relative low sample volume and labor-saving.Most reported online SPE-LC were set up with multiposition valve and additional pumps for sample loading and using the guard column as the SPE to trap analytes.It makes the construction of online system is high cost and the selection of SPE is limited.The other choice is using one of the HPLC pumps to load sample on the base of on-column focusing technique.It is simple and economic, but usually not so effective because of the serious extra-column effect.