One of modern analytical chemistry main challenges is providing as fast as possible results in different application fields. In this view, real-time analysis techniques are experiencing ...ever-increasing success as they can provide data quickly, almost without sample preparation steps. Most of real-time approaches are based on direct mass spectrometry (DMS), a method of analyzing samples without the need for separation or pre-treatment steps. Instead, the sample is directly introduced into the mass spectrometer for analysis. In this context, ambient ionization mass spectrometry (AIMS) techniques are widely represented and successfully used. Extractive-liquid sampling electron ionization-mass spectrometry (E-LEI-MS) represents a different analytical strategy that allows coupling ambient sampling with electron ionization (EI), avoiding any sample preparation step and providing identification based on the comparison with the National Institute of Standards and Technology (NIST) library spectra. E-LEI-MS consists of a dispositive for solvent release and sampling at ambient conditions coupled with an EI source of a single quadrupole mass spectrometer. A micromanipulator allows fine (x,y,z) positioning of a sampling tip. MS can operate in scan or SIM modes depending on the application goals and requirements. Several preliminary successful results were already obtained due to the highly informative EI mass spectra generation. The system was applied to the analysis of active ingredients in pharmaceutical tablets, pesticides on fruit peel, a drug of abuse (cocaine) determination in banknotes, and analysis of unknown components on painting surfaces. Both forensic and artwork applications allowed determining the spatial distribution of the analytes. Here we present a proof-of-concept of E-LEI-MS for targeted/non-targeted analysis and semi-quantitative detection.
An LC‐MS method for the analysis of personal care and household products without sample preparation is presented. The method takes advantage of the Direct‐electron ionization (EI) LC‐MS interface for ...the quantitation of principal components, as well as for the identification of unknown or undeclared ingredients. The technique has proven its inertness toward matrix effects and the electron ionization allows quantitation and library identification. Commercially available products (shower gel, perfume, and hand cream) were diluted with methanol and injected directly into a nano‐LC column. Limonene, linalool, and citral were selected as target compounds because of their use as fragrances in toiletry and detergent products. These and all other fragrances are commonly determined with GC‐MS analysis, prior to sample cleanup, a procedure that can lead to analytes loss. The selected compounds are not detected with ESI because of their poor or very low response. Figures of merit and validation studies were executed and special attention was devoted to matrix‐effects evaluation, because a sample preparation procedure is not involved. No matrix effects were observed, and the repeatability was excellent even after several weeks of operation. Products composition was investigated in full scan mode to determine the presence of unknown or not listed ingredients.
Extra virgin olive oil (EVOO) is one of the main ingredients of the Mediterranean diet. It is claimed as a functional food for its unique content of health-promoting compounds. Tyrosol (Tyr), ...Hydroxytyrosol (Htyr), and their phenolic derivatives present in EVOO show beneficial properties, and their identification and quantification, both in their free form and after the hydrolysis of more complex precursors, are important to certify its quality. An alternative method for quantifying free and total Tyr and Htyr in EVOO is presented using an LC–MS interface based on electron ionization (EI), called liquid electron ionization (LEI). This method requires neither sample preparation nor chromatography; the sample is diluted and injected. The selectivity and sensitivity were assessed in multiple reaction monitoring mode (MRM), obtaining confirmation and quantification in actual samples ranging from 5 to 11 mg/Kg for the free forms and from 32 to 80 mg/Kg for their total amount after hydrolysis. Two MS/MS transitions were acquired for both compounds using the Q/q ratios as confirmatory parameters. Standard addition calibration curves demonstrated optimal linearity and negligible matrix effects, allowing a correct quantification even without expensive and difficult to find labeled internal standards. After several weeks of operation, the system’s repeatability was excellent, with an intraday RSD (%) spanning from five to nine and an interday RSD (%) spanning from 9 to 11.
This work presents a sustainable and rapid method for halogenated pesticide analysis without chromatographic separation. The system is composed of a microfluidic open interface (MOI) for solid-phase ...microextraction (SPME) liquid phase desorption, connected to a liquid electron ionization mass spectrometry interface (LEI-MS). Either a triple quadrupole mass spectrometer (QQQ-MS/MS, (low-resolution) or a quadrupole-time-of-flight tandem MS (QTOF-MS/MS, high-resolution) were employed, each operating in negative chemical ionization (NCI) conditions. The flow rate used (100 µL/min) to rapidly empty the MOI chamber (approximately 2.5 µL) is reduced to the working flow rate of the LEI interface (500 nL/min) by a passive flow splitter (PFS). NCI is an appropriate ionization technique for electrophilic compounds, increasing specificity and reducing background noise. Two halogenated pesticides, dicamba and tefluthrin, were extracted simultaneously from a commercial formulation matrix (CF) using a C18 fiber by direct immersion (3 min under vortex agitation). Analyte desorption occurred in static conditions inside MOI filled with acidified acetonitrile (ACN) (0.2% phosphoric acid, PA). Extraction and desorption steps were optimized to increase efficiency and accelerate the process. No chromatographic separation was involved; therefore, the system fully exploited MS/MS selectivity and HRMS accuracy demonstrating good linearity, repeatability and limits of detection (LODs) and limits of quantification (LOQs) in the pg/mL range (50 and 500 pg/mL, respectively). Low-resolution experiments showed that matrix effects (ME) did not affect the results. The fast workflow (5 min) makes the system suitable for high-throughput analysis observing the principles of green analytical chemistry (GAC).
Mass spectrometry is the most powerful technique for the detection and identification of organic compounds. It can provide molecular weight information and a wealth of structural details that give a ...unique fingerprint for each analyte. Due to these characteristics, mass spectrometry-based analytical methods are showing an increasing interest in the scientific community, especially in food safety, environmental, and forensic investigation areas where the simultaneous detection of targeted and nontargeted compounds represents a key factor. In addition, safety risks can be identified at the early stage through online and real-time analytical methodologies. In this context, several efforts have been made to achieve analytical instrumentation able to perform real-time analysis in the native environment of samples and to generate highly informative spectra. This review article provides a survey of some instrumental innovations and their applications with particular attention to spray-based MS methods and food analysis issues. The survey will attempt to cover the state of the art from 2012 up to 2017.
This review article traces the history of the use of liquid chromatography coupled with mass spectrometry (LC-MS) using electron ionization (EI) from the first attempts up to the present day. At the ...time of the first efforts to couple LC to MS, 70 eV EI was the most common ionization technique, typically used in gas chromatography-mass spectrometry (GC-MS) and providing highly reproducible mass spectra that could be collated in libraries. Therefore, it was obvious to transport this dominant approach to the early LC-MS coupling attempts. The use of LC coupled to EI-MS is challenging mainly due to restrictions related to high-vacuum and high-temperature conditions required for the operation of EI and the need to remove the eluent carrying the analyte before entering the ion source. The authors will take readers through a journey of about 50 years, showing how through the succession of different attempts it has been possible to successfully couple LC with EI-MS, which in principle appear to be incompatible.
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•EI in LC-MS represents a powerful alternative to API sources.•LC-EI-MS does not suffer from matrix effects.•EI in LC-MS enhances identification capabilities in complex matrices.•An EI source allows GC-MS and LC-MS to coexist in a single instrument.•Non-ESI amenable, low-polar compounds can be analyzed with LC-EI-MS.
Proposed structure of the C18-silica/binary solvent interphase and location of Tempol probe: (a) ACN/water 50/50; (b) ACN
<
50%; (c) ACN
>
50%.
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► At ACN/water 50/50, C18 chains form ...an ordered layer and the probe is easily extracted from the hydrophobic layer. ► At 20%
<
ACN
<
50%, the C18 chains collapse on the silica surface and trap the probe into the interphase. ► At ACN
>
50% the chains are disordered but do not collapse on the silica and the probe may be extracted. ► In MeOH/water, the probe is adsorbed into a poorly ordered interphase. ► The endcapping procedure does not allow chain ordering and Tempol is less adsorbed at the interphase with respect to non-endcapped C18-silica.
The structure of the octadecyl (C18) chain layer attached to a silica surface in the presence of binary solvents (acetonitrile/water; methanol/water) was investigated by electron paramagnetic resonance (EPR) and reverse-phase high-performance liquid chromatography (RP-HPLC), using 4-hydroxy-2,2,6,6 tetramethylpiperidine-
N-oxyl (Tempol) to mimic the behavior of pollutants with medium–low polarity. The computer-aided analysis of the EPR spectra provided structural and dynamical information of the probe and its environments which clarified the modifications of the chain conformations that occur at different solvent compositions. Capacity factors,
k′, were calculated as a function of the percentage of water/organic solvent (mobile phase), and the retention behavior of the C18-functionalized silica surface (stationary phase) was compared with the results obtained with EPR analysis under static conditions. In particular, EPR analysis showed that, at percentages of ACN equal or higher than 50%, the chain layer assume a quite ordered structure, whereas at percentages lower than 50% the chains tend to collapse and fold on the silica surface. In this latter situation, the hydrophobic net of the C18 chains strongly limits Tempol mobility. In methanol/water mixtures, both EPR and RP-HPLC analysis showed that the probe was adsorbed into a poorly ordered interphase. If the residual silanols at the silica surface were bonded to a sililating agent (endcapping), both EPR and RP-HPLC analysis showed a decreased adsorption of the probe with respect to the non-endcapped silica at the same mobile phase composition.
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