Automated SPME-SICRIT-MS for the Rapid Screening of Contaminants
Traditional chromatographic methods for contaminant analysis are often limited by extensive sample preparation. This article details a high-throughput, automated workflow coupling Solid Phase Microextraction (SPME) with ambient ionization mass spectrometry, enabling sample-to-result times of under 10 minutes. This approach provides a direct-to-MS analysis for rapid screening in complex food and environmental matrices.
An Automated Workflow for Rapid Contaminant Screening by SPME-SICRIT-MS
The analysis of contaminants in complex matrices such as food and environmental samples requires methods that are not only sensitive and specific but also efficient. Established methods like Gas Chromatography/Mass Spectrometry (GC/MS) and Liquid Chromatography/Mass Spectrometry (LC/MS) often involve multi-step sample preparation protocols and chromatographic separations that can extend analysis times, creating a bottleneck in high-throughput laboratories.
Ambient ionization mass spectrometry (AIMS) techniques offer an alternative by enabling direct analysis with minimal sample handling, significantly reducing the time from sample to result. This article discusses a fully automated workflow, detailed in a new Application Note, which couples automated Solid Phase Microextraction (SPME) using a PAL RTC System with Soft Ionization by Chemical Reaction in Transfer (SICRIT), a commercially available Dielectric Barrier Discharge Ionization (DBDI) source.
The PAL System as an Automation Platform for SPME
Solid Phase Microextraction (SPME) is a solvent-free sample preparation technique that combines extraction, concentration, and sample introduction into a single step. The PAL System serves as a versatile robotic platform, precisely controlling all parameters of the SPME process, i.e., incubation time, temperature, agitation speed, extraction time, and desorption, to ensure high reproducibility. This workflow utilizes the PAL SPME Arrow, which features a robust design and a larger volume and surface area of sorbent material compared to traditional SPME fibers. These features provide greater mechanical stability and increased extraction capacity, leading to higher sensitivity and faster extraction kinetics.
The SICRIT Ion Source: A Soft and Tunable Ionization Interface
The SICRIT source is a DBDI plasma-based source that operates at atmospheric pressure. It is considered a "soft" ionization technique that primarily generates protonated molecules ([M+H]+) with minimal fragmentation, which simplifies spectral interpretation and is crucial for confident compound identification. Studies have shown that SICRIT is effective for a wide range of analytes, from volatile and nonpolar compounds to microbial metabolites and illicit drugs. A key feature of DBDI sources is the ability to modify the gas-phase chemistry to optimize ionization for specific analyte classes. While proton transfer is efficient for many polar analytes, non-polar compounds with low proton affinity, such as Polycyclic Aromatic Hydrocarbons (PAHs), show limited ionization efficiency under standard conditions. As demonstrated by Huba et al. (2018), introducing an easily ionizable "dopant" like fluorobenzene into the carrier gas shifts the dominant ionization pathway from proton transfer to charge transfer. This results in the preferential formation of radical cations ([M]⋅+), significantly enhancing the signal intensity for these challenging compounds. This tuneability makes the SICRIT source a highly versatile tool for broad-based screening.
An Integrated, High-Throughput Analytical Workflow
The workflow detailed in the new Application Note couples these two technologies for a seamless, automated analysis.
The PAL RTC System performs the SPME Arrow extraction and then thermally desorbs the concentrated analytes directly into the SICRIT ion source for immediate MS analysis. The method's performance was validated for several compounds, demonstrating high linearity (R2>0.99) and sensitivity, with Limits of Detection (LODs) in the low picogram-per-milliliter range. The robustness of the workflow was confirmed on complex matrices, including the successful non-target screening of pesticides in soil and the accurate quantification of the insecticide sulfotep in an apple matrix. The use of complementary ionization techniques is increasingly recognized as a strategy to expand the coverage of the metabolome. Studies comparing SICRIT to electrospray ionization (ESI) have found that it effectively ionizes a different set of metabolites, showing a particular efficiency for lipids in positive mode. The ability of the PAL System to automate the interface between advanced extraction techniques like SPME Arrow and novel ionization sources like SICRIT opens up new possibilities for comprehensive and efficient chemical analysis.
The automated coupling of SPME and SICRIT-MS via the PAL RTC platform provides a robust and rapid method for contaminant screening. The workflow leverages the high enrichment factor of SPME Arrow with the soft and tunable ionization of the SICRIT source.
For a detailed description of the experimental parameters, validation data, and full results, please refer to the complete Application Note.
PAL System Application Note. "Automated SPME-SICRIT-MS for Rapid Screening of Contaminants in Food and Environmental Matrices." PAL System, Zwingen, Switzerland, 2025.
Huba, A. K., Mirabelli, M. F., & Zenobi, R. "High-throughput screening of PAHs and polar trace contaminants in water matrices by direct solid-phase microextraction coupled to a dielectric barrier discharge ionization source." Analytica Chimica Acta 1030 (2018) 125-132. https://doi.org/10.1016/j.aca.2018.05.050
McAtamney, A., et al. "Microbial Metabolomics' Latest SICRIT: Soft Ionization by Chemical Reaction In-Transfer Mass Spectrometry." Journal of the American Society for Mass Spectrometry 35 (2024) 3049-3056. https://doi.org/10.1021/jasms.4c00309
Weber, M., Wolf, J. C., & Haisch, C. "Effect of Dopants and Gas-Phase Composition on Ionization Behavior and Efficiency in Dielectric Barrier Discharge Ionization." Journal of the American Society for Mass Spectrometry, 34(3), 538-549 (2023).
Conway, C., et al. "Rapid desorption and analysis for illicit drugs and chemical profiling of fingerprints by SICRIT ion source." Drug Testing and Analysis, 16(10), 1094-1101 (2024). https://doi.org/10.1002/dta.3623
