Drop-on-Demand Sample Introduction System Coupled with the Flowing Atmospheric-Pressure Afterglow for Direct Molecular Analysis of Complex Liquid Microvolume Samples

Abstract

One of the fastest developing fields in analytical spectrochemistry in recent years is ambient desorption/ionization mass spectrometry (ADI-MS). This burgeoning interest has been due to the demonstrated advantages of the method: simple mass spectra, little or no sample preparation, and applicability to samples in the solid, liquid, or gaseous state. One such ADI-MS source, the flowing atmospheric-pressure afterglow (FAPA), is capable of direct analysis of solids just by aiming the source at the solid surface and sampling the produced ions into a mass spectrometer. However, direct introduction of significant volumes of liquid samples into this source has not been possible, as solvent loads can quench the afterglow and, thus, the formation of reagent ions. As a result, the analysis of liquid samples is preferably carried out by analyzing dried residues or by desorbing small amounts of liquid samples directly from the liquid surface. In the former case, reproducibility of sample introduction is crucial if quantitative results are desired. In the present study, introduction of liquid samples as very small droplets helps overcome the issues of sample positioning and reduced levels of solvent intake. A recently developed “drop-on-demand” (DOD) aerosol generator is capable of reproducibly producing very small volumes of liquid (~17 pL). In this paper, the coupling of FAPA-MS and DOD is reported and applications are suggested. Analytes representing different classes of substances were tested and limits of detections were determined. Matrix tolerance was investigated for drugs of abuse and their metabolites by analyzing raw urine samples and quantification without the use of internal standards. Limits of detection below 2 µg/mL, without sample pretreatment, were obtained.

Halo-Shaped Flowing Atmospheric Pressure Afterglow: A Heavenly Design for Simplified Sample Introduction and Improved Ionization in Ambient Mass Spectrometry

“…An auxiliary helium flow of ~100 mL/min through a home-made glass funnel was used to transfer droplets into the central channel of the h-FAPA as was done previously. 9 …”

Critical assessment of ionization patterns and applications of ambient desorption/ionization mass spectrometry using FAPA–MS

“…[12] In contrast to ion sources such as direct analysis in real time, no additional heat source is necessary for thermal desorption in the afterglow region due to the inherent heating of the APGD, leading to afterglow temperatures of~50-250°C. [11,13] So far, the FAPA source has been used for applications such as the detection of explosives and pesticides, [9,13] the analysis of human urine [14] or the identification of compounds in airborne particulate matter. [15] Commonly, the source is described as a soft ionization technique that favors the formation of quasimolecular ions, yielding [M + H] + and [M À H] À in the positive and the negative mode, respectively.…”

An overview of recent developments in metabolomics and proteomics – phytotherapic research perspectives

“…Compared to NMR, MS analyses require extensive sample preparation and further separation procedures make the analysis time-consuming. However, the limitation is minimized with the development of atmospheric sample introduction techniques, where no sample preparation or separation is required (Schaper et al 2012).…”