Towards a miniaturized on-site nano-high performance liquid chromatography electrospray ionization ion mobility spectrometer with online enrichment

Abstract

Safeguarding water quality is resource-intensive and costly. Especially in cases of accidents or disasters, compact devices that allow quick assessment of the current situation are lacking. The objective of this work is the development of a portable measuring device for on-site detection of pollutants in water based on nano-high performance liquid chromatography (nano-HPLC) and electrospray ionization (ESI) ion mobility spectrometry (IMS). Integrated online enrichment by means of solid phase extraction (SPE) further improves sensitivity. In this work, an SPE cartridge exchange unit is presented, which was developed by additive manufacturing in a cost-effective and resource-efficient way. Prerequisites are an easy adaptation to commercially available SPE cartridges and pressure stability of up to 50 bar. In addition, a compact ESI-IMS with 75 mm drift tube length and a resolving power of R = 100 is presented that enables ionization, separation based on ion mobility and detection of analytes at a flow rate of 0.6 – 1.8 µL/min from the liquid phase. This approach also allows miniaturization of the overall system leading to a reduction in energy requirements and the amount of solvents used. For future environmentally benign systems, complete elimination of toxic solvents would be ideal. Therefore, acetonitrile and the nontoxic ethanol are compared as organic mobile phase in terms of elution and ionization efficiency. For characterization, a test mixture containing relevant target analytes, such as chlortoluron, isoproturon, pyrimethanil, mepanipyrim, cyprodinil and carbamazepine, is analyzed. In addition, the analytical greenness metric approach tool is used to evaluate the overall system in terms of its green credentials. It was shown that ethanol can be well used as an organic solvent for the mobile phase and even exhibits better ionization than acetonitrile for the selected model analytes. Furthermore, a relatively high orthogonality of O=0.53 and an effective 2D peak capacity of 2Dneff=174 are reached. Due to the overall miniaturization and splitless coupling, the aims of green chemistry can be met, and ideally a value of 0.92 can be achieved using the AGREE tool for the presented system.