Modular electrospray interface with dual contactless conductometric and ultraviolet photometric detection for...

Capillary electrophoresis (CE) coupled with electrospray ionization mass spectrometry (ESI-MS) is a powerful tool for biomolecule analysis. Integrating on-capillary detectors, such as contactless conductometric (C⁴D) and ultraviolet photometric (UV-PD), before the ESI emitter provides complementary information, overcoming the limitations of single detection methods. This study presents a modular sheath liquid CE-ESI-MS interface incorporating a 2-in-1 detector that combines C⁴D and UV-PD at a single measurement point. The modular interface, including the 2-in-1 detector, was fabricated using 3D printing, enabling flexible customization. The ESI-MS module was adapted from the nanoCEasy interface. The 2-in-1 detector employed a 280 nm or 255 nm UV light-emitting diode as the light source, while C⁴D electrodes were cast into the 3D-printed module using Wood's metal. The performance of the dual-detection system was evaluated using lysozyme, amino acids extracted from cherry tomato and banana, and peptides obtained from trypsin-digested bovine serum albumin (BSA). Differences in the effective lengths between the 2-in-1 detector and the MS system led to time-scale deviations, which were corrected using effective electrophoretic mobility. The integration of dual detection with CE-ESI-MS enhances sample throughput and data acquisition. The modular design and 3D printing approach offer a simple, cost-effective method for implementing dual-detection in CE-MS.