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Highly sensitive splitless programmed temperature vaporizing (PTV)-large volume injection (LVI)-GC-MS-negative chemical ionization (NCI) method was developed and validated for the trace detection of explosives and related compounds from environmental matrices. Traditional LVI analysis, whether performed through solvent-vent mode PTV or on-column systems, is characterised by improved detection limits but has limited performance in multi-target and screening applications. Our new approach can reach trace detection levels within a broad range of molecular volatilities (4 orders of magnitude), including volatile compounds, and it represents the first time that this approach has been applied to assess challenging explosive compounds. This is attributed to a unique double-column configuration setup developed for the efficient removal of excess solvent through a flame detector before reaching the MS, with the precise timing of carrier-gas flows and the heating program. The new method simultaneously achieves record-high sensitivities for military and improvised explosives, related by-products and taggants. Detection and quantification limits of 0.1 pg μL−1(2 pg on column) with a linear dynamic range of at least 2 orders of magnitude, as well as high precision (<20% RSD) and accuracy (<±30%), were determined for most of the compounds. When applying this method to the analysis of spiked soil samples, a detection limit of 0.5 ng g−1was successfully obtained. This high-performance method may be used for the trace analysis of explosives in real world samples. The principles of the proposed method can be further adjusted to fit other compound families where high sensitivity and broad range of screening are desired.

Complex mixtures, characterized by high density of compounds, challenge trace detection and identification. This is further exacerbated in nontargeted analysis, where a compound of interest may be well hidden under thousands of matrix compounds. We studied the effect of matrix complexity on nontargeted detection (peak picking) by LC–MS/MS (Orbitrap) analysis. A series of ∼20 drugs, V-type chemical warfare agents and pesticides, simulating toxic unknowns, were spiked at various concentrations in several complex matrices including urine, rosemary leaves, and soil extracts. Orbitrap “TraceFinder” software was used to explore their peak intensities in relation to the matrix (peak location in an intensity-sorted list). Average practical detection limits of nontargets were determined. While detection among the first 10,000 peaks was achieved at 0.3–1 ng/mL levels in the extract, for the more realistic “top 1000” list, much higher concentrations were required, approaching 10–30 ng/mL. A negative power law functional dependence between the peak location in an intensity-sorted suspect list and the nontarget concentration is proposed. Controlled complexity was explored with a series of urine dilutions, resulting in an excellent correlation between the power law coefficient and dilution factor. The intensity distribution of matrix peaks was found to spread (unevenly) on a broad range, fitting well the Weibull distribution function with all matrices and extracts. The quantitative approach demonstrated here gives a measure of the actual capabilities and limitations of LC–MS in the analysis of nontargets in complex matrices. It may be used to estimate and compare the complexity of matrices and predict the typical detection limits of unknowns.