Commercially available trypsin IMERs can digest proteins with high sequence coverage and robustness, facilitating online multidimensional LC–MS.
New separation techniques for the analysis of polar and ionic analytes have aroused great interest in the field of metabolomics and environmental investigation in the past two decades. Hydrophilic interaction liquid chromatography (HILIC) is a promising tool to address this challenge. HILIC separation is based on the polarity of analytes, which generally show stronger retention with increasing polarity according to the HILIC separation mechanism. Furthermore, the high content of organic solvent in the mobile phase leads to good ionization properties in the electrospray ionization (ESI), and consequently enhances the detection sensitivity by hyphenated mass spectrometry (MS) detector.