For the analyses with Asahipak NH2P-50 column, it is recommended to use a line filter, NH2P-LF. Here, the way how to connect NH2P-LF is explained. As shown in the figure below, NH2P-LF should be installed upstream of the injector. NH2P-LF is used to trap the extraneous substances in the eluent and not in the sample. Therefore, sample pretreatment and/or use of guard column is still necessary to prevent the deterioration of column by the impurities in the sample.