Chemical Fingerprinting of Olive Oils by Electrospray Ionization-Differential Mobility Analysis-Mass Spectrometry: A New Alternative to Food Authenticity Testing.

Recently, the olive oil industry has been the subject of harsh criticism for false labeling and even adulterating olive oils. This situation in which both the industry and the population are affected leads to an urgent need to increase controls to avoid fraudulent activities around this precious product. The aim of this work is to propose a new analytical platform by coupling electrospray ionization (ESI), differential mobility analysis (DMA), and mass spectrometry (MS) for the analysis of olive oils based on the information obtained from the chemical fingerprint (nontargeted analyses). Regarding the sample preparation, two approaches were proposed: (i) sample dilution and (ii) liquid-liquid extraction (LLE). To demonstrate the feasibility of the method, 30 olive oil samples in 3 different categories were analyzed, using 21 of them to elaborate the classification model and the remaining 9 to test it (blind samples). To develop the prediction model, principal component analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLS-DA) were used. The overall success rate of the classification to differentiate among extra virgin olive oil (EVOO), virgin olive oil (VOO), and lampante olive oil (LOO) was 89% for the LLE samples and 67% for the diluted samples. However, combining both methods, the ability to differentiate EVOO from lower-quality oils (VOO and LOO) and the edible oils (EVOO and VOO) from nonedible oil (LOO) was 100%. The results show that ESI-DMA-MS can become an effective tool for the olive oil sector.

Tandem Ion Mobility Spectrometry for the Detection of Traces of Explosives in Cargo at Concentrations of Parts Per Quadrillion.

A tandem ion mobility spectrometer (IMS2) built from two differential mobility analyzers (DMAs) is coupled at ambient pressure with a thermal fragmenter placed in between, such that the precursor ions selected in the first DMA are thermally decomposed at ambient pressure in the fragmenter and the product ions generated are filtered in the second DMA. A thermal desorber and a multicapillary gas chromatography (GC) column are coupled to a secondary electrospray (SESI) ion source, so the adsorption sampling filters are thermally desorbed and the liberated vapors are separated in the GC column, prior to their ionization and mobility/mobility classification. The new fragmenter allows the fragmentation of the five explosives studied: RDX, PETN, NG, EGDN, and TNT. The background of the analyzer is evaluated for the five explosives using air samples of 500 L volume. An atmospheric background of only 2.5 pg (5 ppq) is found for TNT, being somewhat higher for the rest of explosives studied. The architecture GC-IMS2 is compared with GC-IMS obtaining a 100-fold increase of sensitivity in the first configuration, confirming the high selectivity provided by the fragmentation cell and the second IMS stage for the product ion mobility analysis. The analyzer is tested also with real explosives hidden in cargo pallets achieving successful detection of four (EGDN, NG, TNT, and PETN) out of five explosives.

Rapid detection of explosive vapors by thermal desorption atmospheric pressure photoionization differential mobility analysis tandem mass spectrometry.

RATIONALE: The increased frequency in the number of international terror threats has led to a corresponding increase in demand for fast, sensitive and reliable screening methods suitable for the detection of airborne explosive vapors. We demonstrate herein a workflow suitable for the determination of nitrogen-based explosives at the picogram level in just minutes. METHODS: A method is described that combines Thermal Desorption (TD) sample introduction with Differential Mobility Analysis (DMA) Tandem Mass Spectrometry (MS/MS), enabling a sensitive and accurate workflow suitable for the rapid detection of trace nitroaromatic, nitroester and nitramine explosive vapors. The methods are bridged using a novel low-flow, field-free Atmospheric Pressure Photoionization (APPI) source, intended specifically for the analysis of gas-phase analytes and airborne particles. RESULTS: Limits of detection within or below the picogram range were determined for the analysis of a range of explosives standards including 2,6-DNT, TNT, TATB, Tetryl, RDX, EGDN, PETN, HMX, and NG. Practical application of the TD-APPI-DMA-MS/MS workflow was demonstrated for the detection of real trace explosive vapors produced from the volatilization of solid explosive samples stored within a sealed cardboard box. A single complete analysis was performed in less than 2 min. CONCLUSIONS: The highly sensitive and accurate detection of a variety of common nitrogen-based explosive vapors has been demonstrated, at levels suitable for practical, high-throughput security screening applications.

Planar Differential Mobility Analyzer with a Resolving Power of 110.

Planar differential mobility analyzers (DMAs) have previously achieved resolving powers of 60-80 in air or N2 at the mobility of the tetraheptylammonium ion (THA+, ∼0.97 cm2/V/s). For unclear reasons, this performance is considerably below the theoretical limit. In this work, a performance close to this ideal limit is attained in SEADM's P5 DMA via improved flow laminarization, under otherwise the same flow conditions as in prior work. The new laminarizer remains effective at unusually large gas velocities (reached with two blowers in series), yielding a resolving power of 110. The selectivity of the improved DMA combined with a mass spectrometer was assessed by the analysis of a real sample of extra virgin olive oil.

Ion Mobility Spectrometer-Fragmenter-Ion Mobility Spectrometer Analogue of a Triple Quadrupole for High-Resolution Ion Analysis at Atmospheric Pressure.

Two differential mobility analyzers (DMAs) acting as narrow band mobility filters are coupled in series, with a thermal fragmentation cell placed in between, such that parent ions selected in DMA1 are fragmented in the cell at atmospheric pressure, and their product ions are analyzed on DMA2. Additional mass spectrometer analysis is performed for ion identification purposes. A key feature of the tandem DMA is the short residence time (∼0.2 ms) of ions in the analyzer, compared to tens of milliseconds in drift tube ion mobility spectrometers (IMS). Ion fragmentation within the analyzer and associated mobility tails are therefore negligible for a DMA but not necessarily so in conventional IMS. This advantage of the DMA is demonstrated here by sharply defined product ion mobility peaks. Ambient pressure ion fragmentation has been previously demonstrated by both purely thermal means as well as rapidly oscillating intense electric fields. Our purely thermal fragmentation cell here achieves temperatures up to 700 °C measured inside the heating coil of a cylindrical ceramic heater, through whose somewhat colder axis we direct a beam of mobility-selected ions. We investigate tandem separation of chloride adducts from the explosives EGDN, nitroglycerine (NG), PETN, and RDX and from deprotonated TNT. Atmospheric pressure fragmentation of the first three ions yields one or several previously reported fragments, providing highly distinctive tandem DMA channels for explosive identification at 1 atm. RDX ions had not been previously fragmented at ambient pressure, yet [RDX + Cl]- converts up to 7% (at 300 °C) into a 166 m/ z product. The known high thermal resilience of TNT is confirmed here by its rather modest conversion, even when the ceramic is heated to 700 °C. At this temperature some previously reported fragments are found, but their mobilities are fairly close to each other and to the one of the far more abundant parent ion, making their identification by mobility alone problematic. We anticipate that moderately higher fragmenter temperatures will produce smaller fragments with mobilities readily separated from that of [TNT - H]-.

Mobility Peak Tailing Reduction in a Differential Mobility Analyzer (DMA) Coupled with a Mass Spectrometer and Several Ionization Sources.

The differential mobility analyzer (DMA) is a narrow-band linear ion mobility filter operating at atmospheric pressure. It combines in series with a quadrupole mass spectrometer (Q-MS) for mobility/mass analysis, greatly reducing chemical noise in selected ion monitoring. However, the large flow rate of drift gas (~1000 L/min) required by DMAs complicates the achievement of high gas purity. Additionally, the symmetry of the drying counterflow gas at the interface of many commercial MS instruments, is degraded by the lateral motion of the drift gas at the DMA entrance slit. As a result, DMA mobility peaks often exhibit tails due to the attachment of impurity vapors, either (1) to the reagent ion within the separation cell, or (2) to the analyte of interest in the ionization region. In order to greatly increase the noise-suppression capacity of the DMA, we describe various vapor-removal schemes and measure the resulting increase in the tailing ratio, (TR = signal at the peak maximum over signal two half-widths away from this maximum). Here we develop a low-outgassing DMA circuit connected to a mass spectrometer, and test it with three ionization sources (APCI, Desolvating-nano ESI, and Desolvating low flow SESI). While prior TR values were in the range 100-1000, the three new sources achieve TR ~ 105. The SESI source has been optimized for maximum sensitivity, delivering an unprecedented gain for TNT of 190 counts/fg, equivalent to an ionization efficiency of one out of 140 neutral molecules. Graphical Abstract ᅟ.