Streamlining regular liquid chromatography with MALDI-TOF MS and NMR spectroscopy using automatic full-contact splitless spotting interface and flash-tap fractioning collection

Chi-Minh Truong; Yung-Cheng Jair; Hong-Po Chen; Wei-Chih Chen; Yi-Hsin Liu; Pin-Chuan Chen; Pai-Shan Chen

doi:10.1016/j.aca.2024.342401

Streamlining regular liquid chromatography with MALDI-TOF MS and NMR spectroscopy using automatic full-contact splitless spotting interface and flash-tap fractioning collection

Anal Chim Acta. 2024 Apr 15:1298:342401. doi: 10.1016/j.aca.2024.342401. Epub 2024 Feb 26.

Authors

Chi-Minh Truong¹, Yung-Cheng Jair², Hong-Po Chen³, Wei-Chih Chen¹, Yi-Hsin Liu³, Pin-Chuan Chen⁴, Pai-Shan Chen⁵

Affiliations

¹ Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
² Institute of Toxicology, College of Medicine, National Taiwan University, Taipei, Taiwan.
³ Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan.
⁴ Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan. Electronic address: pcchen@mail.ntust.edu.tw.
⁵ Institute of Toxicology, College of Medicine, National Taiwan University, Taipei, Taiwan. Electronic address: paishanchen@ntu.edu.tw.

PMID: 38462340
DOI: 10.1016/j.aca.2024.342401

Abstract

Background: High-resolution matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and nuclear magnetic resonance (NMR) spectroscopy are powerful tools to identify unknown psychoactive substances. However, in complex matrices, trace levels of unknown substances usually require additional fractionation and concentration. Specialized liquid chromatography systems are necessary for both techniques. The small flow rate of nano LC, typically paired with MALDI-TOF MS, often results in prolonged fractionation times. Conversely, the larger flow rate of semi-preparative LC, used for NMR analysis, can be time-consuming and labor-intensive when concentrating samples. To address these issues, we developed an integrated automatic system that integrated to regular LC.

Result: Automatic spot collector (ASC) and automatic fraction collector (AFC) were present in this study. The ASC utilized in-line matrix mixing, full-contact spotting and real time heating (50 °C), achieving great capacity of 5 μL droplet on MALDI plate, high recovery (76-116%) and rapid evaporation in 2 min. The analytes were concentrated 4-8 times, forming even crystallization, reaching the detection limit at the concentration of 50 μg L^-1 for 12 psychoactive substances in urine. The AFC utilizes flexible tubing which flash-tapped the microtube's upper rim (3 mm depth) instead of reaching the bottom. This method prevents sample loss and minimizes the robotic arm's movement, providing a high fractionating speed at 6 s 12 psychoactive compounds were fractionated in a single round analysis (recovery: 81%-114%). Methamphetamine and nitrazepam obtained from drug-laced coffee samples were successful analyzed with photodiode array (PDA) after one AFC round and NMR after five rounds.

Significance: The ASC device employed real-time heating, in-line matrix mixing, and full-contact spotting to facilitate the samples spotting onto the MALDI target plate, thereby enhancing detection sensitivity in low-concentration and complex samples. The AFC device utilized the novel flash-tapping method to achieve rapid fractionation and high recovery rate. These devices were assembled using commercially available components, making them affordable (400 USD) for most laboratories while still meeting the required performance for advanced commercialized systems.

Keywords: Automation; Fractioning and spotting; Liquid chromatography; Matrix-assisted laser desorption/ionization-time of flight-mass spectrometry; Nuclear magnetic resonance spectroscopy.

MeSH terms

Chromatography, Liquid / methods
Crystallization
Magnetic Resonance Spectroscopy
Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization* / methods