For comprehensive pesticide analysis, laboratories typically operate two platforms—GC-EI for volatile compounds and LC-ESI for polar or low-volatility substances—with GC-EI losing selectivity in complex matrices due to dense fragmentation patterns. A DBDI-based ion source instead preserves the intact molecular ion, making GC data interpretable against existing LC-MS/MS libraries. Drawing on calibration and application data from 687 pesticides, this article shows how this blurs the boundary between the previously separate domains of GC-MS and LC-MS.
Two Platforms for Comprehensive Pesticide Analysis
For comprehensive pesticide residue analysis, laboratories today generally operate two separate systems. Volatile, non-polar compounds are captured by gas chromatography with electron impact ionization (GC-EI), while polar and high-molecular-weight substances are captured by liquid chromatography with electrospray ionization (LC-ESI). This split follows not so much the separation technique itself as the underlying ionization principles: hard EI ionization requires analytes to be transferred into the gas phase and produces characteristic fragmentation spectra, while gentle ESI ionization relies on dissolved analytes and yields intact molecular ions—with particularly high sensitivity for polar, protonatable substances. Because real-world pesticide lists routinely contain both compound classes, laboratories need both platforms in parallel to achieve full coverage of the relevant compound space—with correspondingly double the effort for instrumentation, method development, spectral libraries, and training.
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Where GC-EI Reaches Its Limits in Complex Matrices
Within this two-platform approach, GC-EI analysis in particular shows systematic weaknesses in complex matrices. In electron impact ionization, analyte molecules are exposed to high-energy electrons, which destroys the molecular ion and produces a characteristic but heavily fragmented pattern of 10 to 20 peaks in the low mass range. In clean matrices at sufficient concentration, this is not a problem. However, in complex real-world samples—food extracts, environmental matrices, agricultural materials—these fragment peaks accumulate in the same, already densely populated low mass range and compete there with matrix signals. The result is a higher manual evaluation burden during peak identification and reduced selectivity near the regulatory Maximum Residue Limit (MRL).
Compounding the issue, regulatory requirements call for at least two identification points for certain substances. If the selected ion monitoring (SIM) signal is not unambiguous, a second measurement run on an LC-MS/MS platform becomes necessary— including renewed, often elaborately adapted sample preparation. For strongly non-polar or poorly protonatable analytes, however, this fallback is sometimes unavailable, since they cannot be ionized under ESI conditions and are consequently lost analytically between the two platforms.
One Ion Source for Both Compound Spaces
One way to address these limitations is to use a new ion source with broad analyte coverage. Plasmion has commercialized such an ion source under the name SICRIT®. It is based on the principle of dielectric barrier discharge ionization (DBDI), in which an alternating voltage generates a cold plasma. Analytes are drawn through the ring-shaped plasma, pulled in by the vacuum of the atmospheric-pressure mass spectrometer. Charge transfer occurs without direct contact between plasma and sample, so the molecule remains largely intact. Instead of the 10 to 20 fragment peaks over which EI spreads the signal intensity, the DBDI ion source concentrates the signal into one or two dominant ion species—predominantly [M+H]⁺ and [M]⁺. Because the source ionizes both polar and non-polar components and can be operated with either GC or LC separation via dedicated coupling modules, it covers nearly the entire analytical space of both previously separate platforms.
Figure 1: Comparison of MS¹ spectra for diazinon: classical EI ionization (left) versus the DBDI ion source (right). While EI produces a heavily fragmented spectrum with more than 20 competing peaks, the intact [M+H]⁺ ion dominates with the DBDI ion source.
Setup, Calibration, and Confirmation Workflow
To test whether the described limitations of GC-EI analysis could be addressed by the alternative ion source, a measurement system was built that couples a GC system to a high-resolution atmospheric-pressure mass spectrometer via a DBDI ion source (GC-DBDI-QTOF). In an initial series of experiments, 74 pesticides from three commercial multi-residue standards were measured across a five-point calibration range from 1 ppb to 1 ppm. Limits of detection (LODs) were calculated according to the EU Commission methodology (3.9 × Sb/slope of the calibration curve). All measurements were performed in untargeted full-scan MS¹ mode, without SIM, MRM (Multiple Reaction Monitoring), or compound-specific optimization.
For confirmatory analysis, data-dependent acquisition (DDA) was used, in which the dominant [M+H]⁺ precursor ion serves as the basis for CID fragmentation. The resulting MS² spectra were matched against an existing LC-MS/MS spectral library. In an extended study, carried out as part of a doctoral project at the Technical University of Munich, the method was scaled up to 687 pesticides from both GC- and LC-suitable compound classes, measured using the same GC-DBDI-QTOF setup.
Detection Sensitivity in Full-Scan Operation
A key question for laboratory use is whether the achievable sensitivity is sufficient for regulatory detection limits. The EU standard maximum residue value is 10 ppb. In the study of 74 pesticides described above, 70 of the 74 compounds achieved LODs below this threshold—in untargeted full-scan mode, that is, without the sensitivity gain from SIM or MRM that is typical for GC-EI. Calibration curves showed strong linearity across all three standards. Reaching regulatory detection limits already in untargeted operation is analytically significant: it points to further optimization potential, for instance through targeted use of SIM or MRM, or by switching to triple-quadrupole systems.
Figure 2: LOD distribution for 74 pesticides on a logarithmic (log₁₀) scale. Reference lines mark the EU standard MRL threshold (10 ppb), 100 ppt, and 10 ppt. All measurements in full-scan MS¹ mode.
MS/MS Confirmation via the LC Library
The remarkable aspect of this method, however, lies in identification: because the DBDI ion source delivers a dominant [M+H]⁺ precursor ion, the confirmation workflow from the LC-MS/MS world can be applied directly to GC data. Data-dependent acquisition (DDA) automatically triggers CID fragmentation for compounds of interest; the resulting MS² spectra are generated from a clearly defined precursor under controlled collision energies—the same experimental framework used in classical LC-MS/MS confirmation. Because the DBDI source delivers an [M+H]⁺ precursor ion—chemically identical to what a classical ESI source produces in LC-MS/MS—these MS² spectra can be matched directly against existing LC-MS/MS spectral libraries, without translation or adaptation. For the model analyte diazinon, the MS² spectrum obtained from the GC-DBDI measurement matched the corresponding LC-MS/MS library entry as the top hit.
Figure 3: GC-DBDI MS² spectrum for diazinon, overlaid with the Shimadzu LC-MS/MS library entry. The correct compound was identified as the top hit.
Substances that were previously detected as a GC peak but could only be unambiguously identified with extra effort due to dense fragmentation patterns can now be confirmed with the same level of confidence previously reserved for LC-MS/MS confirmation—without requiring a separate measurement run with renewed sample preparation.
687 Pesticides: When GC Analysis Reaches into the LC Domain
How far this effect can be scaled was investigated in the previously mentioned study of 687 pesticides from both GC- and LC-suitable compound classes. Already in an initial, non-optimized run, 99.1 percent of the compounds were detected. Notably, even classically LC-dependent, polar substances were captured solely via GC separation, without any derivatization—possible because DBDI ionization is not limited to polar or non-polar analytes, and these substances evidently vaporized without decomposing under the chosen GC conditions. A single GC run can thus cover a large part of the compound space that has so far necessarily been reserved for LC. The linear dynamic range exceeded three orders of magnitude, and sensitivity met EU MRL thresholds for all detected compounds. Switching from helium to hydrogen as the carrier gas further reduced the run time by around 40 percent, to 15 minutes, with the same chromatographic resolution and no loss in MS performance or spectral quality.
Figure 4: Simultaneous GC-DBDI-MS analysis of 687 pesticides (GC- and LC-suitable compound classes) in a matrix. Run time 15 min with hydrogen as carrier gas. LODs meet EU MRL requirements (< 10 ppb).
What This Means for Laboratory Infrastructure
These effects have a direct infrastructural dimension. A laboratory that operates GC-MS and LC-MS as separate platforms typically maintains two mass spectrometers, two ionization sources, two spectral library formats, and two method development pipelines. With a shared ion source for GC and LC, both separation methods share the same ion chemistry, spectral library, and confirmation workflow. This does not make GC-EI and LC-ESI obsolete — there remain applications that specifically rely on EI fragmentation patterns for identification, or compounds that cannot tolerate GC separation and depend on ESI. For the growing share of substances that can be covered across both compound spaces with a single ionization approach, however, the effort required for instrument infrastructure, method development, maintenance, and training is noticeably reduced.
Figure 5: Shimadzu Nexis GC-2030, Sicrit GC module & Shimadzu LC 9030 QTOF.
A Shifted Boundary Between GC and LC
The decisive shift is not that GC and LC are measured simultaneously in a single run, but that the boundary between the two domains moves. A soft-ionizing source makes classically LC-dependent substances accessible via GC separation and allows their confirmation using the same LC-MS/MS libraries that were previously usable only for LC data. Laboratories that have so far operated GC-MS and LC-MS as separate worlds can, on this basis, consolidate their duplicate instrument infrastructure for a growing portion of the pesticide spectrum under investigation, without sacrificing the analytical depth of either method. How far this effect can be extended to triple-quadrupole systems and larger, routinely used compound lists remains to be shown by further work.
