Liquid chromatography-electron ionization tandem mass spectrometry with the Direct-EI interface in the fast determination of diazepam and flunitrazepam in alcoholic beverages

Sample Injection for Real-Time Analysis (SIRTA) Using GC-MS with Cold EI

There is a continual demand for advanced methods and instruments for real-time analysis (RTA). Most of the current RTA techniques based on MS involve ambient desorption ionization technology. However, flow injection of liquid extracted samples is another option without added modifications or cost to existing LC-MS instruments. In this work, we introduce a new RTA approach named sample injection for real-time analysis (SIRTA) using GC-MS with Cold EI. In SIRTA, the standard GC column is replaced with a 1 m long 0.1 mm I.D. fused silica capillary that connects the GC injector to the MS transfer-line of Cold EI. Thus, SIRTA with Cold EI imposes no need for any additional instrumentation; hence, it is characterized by zero added cost. Like in flow injection in MS of LC-MS, the sample is dissolved in ∼1 mL methanol or another solvent. Subsequently, the vial is placed in the GC-MS autosampler while using a standard syringe for injection without any GC separation. The analysis takes merely 0.2-0.7 min, ensuring rapid and consecutive analyses. Unlike standard EI, Cold EI enables SIRTA by taking advantage of its fly through open ion source to avoid overwhelming the ion source during the elution of solvents while still providing enhanced molecular ions for nearly all analytes. In this study, we demonstrated SIRTA Cold EI analysis of 12 compounds and 7 mixtures, including various prescription and illicit drugs, cannabis and petroleum samples, and other synthetic organic compounds including those with molecular weight up to 800 g/mol.

The overshadowed role of electron ionization-mass spectrometry in analytical biotechnology

Target and untargeted analysis of several compounds are crucial methods in important areas such as omics sciences. Gas chromatography coupled to mass spectrometry (GC-MS) is widely used for volatile and thermally stable compounds. In this case, the electron ionization technique (EI) is preferable as it produces highly fragmented and reproducible spectra comparable to spectral libraries. However, only a fraction of target compounds is analyzable by GC without chemical derivatization. Therefore, liquid chromatography (LC) coupled with MS is the most used technique. Contrary to EI, electrospray ionization does not produce reproducible spectra. That is why researchers have been working on interfaces between LC and EI-MS to bridge the gap between those techniques. This short review will discuss advancements, applications, and perspectives on biotechnological analysis.

NanoLC-EI-MS: Perspectives in Biochemical Analysis

Although LC-MS with atmospheric pressure ionization (API) sources is the primary technique used in modern bioanalytical studies, electron ionization mass spectrometry (EI-MS) can provide some substantial advantages over it. EI-MS is a matrix effect-free technique that provides reproducible and comparable mass spectra, serving as a compound fingerprint for easy identification through automated comparison with spectral libraries. Leveraging EI-MS in biochemical studies can yield critical analytical benefits for targeted and untargeted analyses. However, to fully utilize EI-MS for heavy and non-volatile molecules, a new technology that enables the coupling of liquid chromatography with EI-MS is needed. Recent advancements in nanoLC have addressed the compatibility issues between LC and EI-MS, and innovative interfacing strategies such as Direct-EI, liquid electron ionization (LEI), and Cold-EI have extended the application of EI-MS beyond the determination of volatile organic molecules. This review provides an overview of the latest developments in nanoLC-EI-MS interfacing technologies, discussing their scope and limitations. Additionally, selected examples of nanoLC-EI-MS applications in the field of biochemical analysis are presented, highlighting the potential prospects and benefits that the establishment of this technique can bring to this field.

The history of electron ionization in LC-MS, from the early days to modern technologies: A review

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.

All solid-state miniaturized potentiometric sensors for flunitrazepam determination in beverages

Flunitrazepam is one of the frequently used hypnotic drugs to incapacitate victims for sexual assault. Appropriate diagnostic tools should be available to victims regarding the growing concern about "date-rape drugs" and their adverse impact on society. Miniaturized screen-printed potentiometric sensors offer crucial point-of-care devices that alleviate this serious problem. In this study, all solid-state screen-printed potentiometric flunitrazepam sensors have been designed. The paper device was printed with silver and carbon ink. Formation of an aqueous layer in the interface between carbon-conducting material and ion-sensing membrane nevertheless poses low reproducibility in the solid-contact electrodes. Accordingly, poly(3,4-ethylenedioxythiophene) (PEDT) nano-dispersion was applied as a conducting hydrophobic polymer on the electrode surface to curb water accumulation. Conditioning of ion-sensing membrane in the vicinity of reference membrane has been considered carefully using special protocol. Electrochemical characteristics of the proposed PEDT-based sensor were calculated and compared favorably to PEDT-free one. The miniaturized device was successfully used for the determination of flunitrazepam in carbonated soft drinks, energy drink, and malt beverage. Statistical comparison between the proposed sensor and official method revealed no significant difference. Nevertheless, the proposed sensor provides simple and user-friendly diagnostic tool with less equipment for on-site determination of flunitrazepam.

Interpol review of controlled substances 2016-2019

This review paper covers the forensic-relevant literature in controlled substances from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

Current developments in LC-MS for pharmaceutical analysis

Liquid chromatography (LC) based techniques in combination with mass spectrometry (MS) detection have had a large impact on the development of new pharmaceuticals in the past decades.

Facile synthesis of copper(II) oxide nanospheres covered on functionalized multiwalled carbon nanotubes modified electrode as rapid electrochemical sensing platform for super-sensitive detection of antibiotic

Herein, we report a super-active electrocatalyst of copper(II) oxide nanoparticles (CuO NPs) decorated functionalized multiwalled carbon nanotubes (CuO NPs@f-MWCNTs) by the ultrasonic method. The as-synthesized CuO NPs@f-MWCNTs was characterized through the FESEM, XPS, XRD and electrochemical impedance spectroscopy (EIS). The combination of highly active CuO NPs and highly conductive f-MWCNTs film with rapid detection enables this nanohybrid to display excellent electrochemical performance towards anesthesia drug. Furthermore, the hybrid electrocatalyst modified SPCE was developed for the determination of flunitrazepam (FTM) for the first time. FTM is important anesthesia drug with high adverse effect in human body. Benefiting from the synergistic reaction of CuO NPs and f-MWCNTs, this nanohybrid exhibited high sensitivity and specificity towards FTM electro-reduction. The CuO NPs@f-MWCNTs film modified SPCE exhibits outstanding electrochemical activity including excellent reproducibility, wide linear range from 0.05 to 346.6 µM with nanomolar limit of detection for FTM detection. Further, the as-modified CuO NPs@f-MWCNTs/SPCE has been applied to determination of FTM in biological and drug samples with satisfactory recovery results, thereby showing a notable potential for extensive (bio) sensor applications.

Combining linear retention index and electron ionization mass spectrometry for a reliable identification in nano liquid chromatography

The present research is focused on the object to improve identification capability in liquid chromatography (LC), by creating a system as similar as possible to gas chromatography (GC), where the combination/complementarity of Linear Retention Index (LRI) and Electron Ionization Mass Spectrometry (EI-MS) data makes the identification process easy, automatic and reliable. Conversely, in LC the untargeted characterization of real-world samples is still a challenge, due to the not repeatable and poorly informative nature of typical atmospheric pressure ionization mass spectrometry, normally hyphenated to LC. In the last decades the miniaturization of LC instrumentation together with the considerable progresses in MS vacuum pump capability has made the LC-EI-MS hyphenation more feasible. In the present work, a prototypal nanoLC-EI-MS system was used for the determination of typically LC-amenable compunds, such as coumarins, furocoumarins and polymethoxyflavones in citrus essential oils. All the compounds provided high quality EI-MS spectra, evaluated by the comparison with thousands of spectra present in commercial EI-MS libraries. Spectral similarities major than 80% were achieved. Furthermore, an LRI system, based on the use of an alkyl aryl ketone homologue reference series, was proposed as additional filter to achieve a univocal identification. Then, a novel dual-filter LRI/EI-MS library was built and resulted very helpful in the case of isomeric compounds characterized by identical EI-MS spectrum, but different retention behaviour. The very low inter-day variability attained for each LRI value, together with the satisfactory chromatographic resolution of the developed method, led to a 100% reliability of the identification process based on LRI.

Evaluation of a liquid electron ionization liquid chromatography-mass spectrometry interface

Liquid Electron Ionization (LEI), is an innovative liquid chromatography-mass spectrometry (LC-MS) interface that converts liquid HPLC eluent to the gas-phase in a mass spectrometer equipped with an electron ionization (EI) source. LEI extends the electronic spectra libraries access to liquid chromatography, providing a powerful tool in the untargeted approacssh. Negligible matrix effects allow accurate quantitative information. The purpose of this research was to evaluate the main aspects concerning the interfacing process. These fundamental studies were necessary to understand the mechanism of LEI in details, and improve the interfacing process, especially regarding robustness and sensitivity. Hardware components were installed to prevent analytes precipitation, reduce thermal decomposition of sensitive compounds, and to stabilize the nano-flow delivery with different mobile-phase compositions. Particular attention was devoted to insulating the heated vaporization area from the LC part of the system. Experiments were performed to optimize the interface inner capillary dimensions, and other operative parameters, including temperature, gas and liquid flow rates. Test compounds of environmental interest were selected based on molecular weight, thermal stability, volatility, and polarity. Robustness was evaluated with a set of replicated injections and calibration experiments using a soil matrix as a test sample. MRM detection limits in the low-picogram range were obtained for five pesticides belonging to different classes in a soil sample. High-quality electron ionization mass spectra of a mixture of pesticides were also obtained.

Development of a Flow Injection System for Differential Pulse Amperometry and Its Application for Diazepam Determination

This work presents the development of a flow injection system for differential pulse amperometry (DPA) for diazepam determination in the presence of oxygen. The thin flow cell consisted of the bare glassy carbon electrode, reference silver/silver chloride, and stainless steel as the auxiliary electrode. Electrochemical reduction of diazepam (DZP) was characterised by cyclic voltammetry. Azomethine reduction peak was used for DZP quantification. The detector response was linear in the range 20-250 µmol/dm³ of diazepam, with a calculated detection limit of 3.83 µg/cm³. Intraday and interday precision were 1.53 and 10.8%, respectively. The method was applied on three beverage samples, energetic drink, and two different beer samples, and obtained recoveries were from 93.65 up to 104.96%. The throughoutput of the method was up to 90 analyses per hour.

Atmospheric Pressure Vaporization Mechanism for Coupling a Liquid Phase with Electron Ionization Mass Spectrometry

A novel liquid chromatography-mass spectrometry (LC-MS) interfacing concept is presented and discussed. The new interface, called liquid-EI (LEI), is based on electron ionization (EI) but, differently from any previous attempt, the vaporization of solutes and mobile phase takes place at atmospheric pressure into a specifically designed region, called "vaporization microchannel", before entering the high-vacuum ion source. The interface is completely independent from the rest of the instrumentation and can be adapted to any gas chromatography/mass spectrometry (GC/MS) system, as an add-on for a rapid LC-MS conversion. Pressure drop and temperature gradient between LC and MS were considered to enhance the analyte response and reduce band broadening and/or solute carryovers. A fused silica liner, placed inside the vaporization microchannel, acts as an inert vaporization surface speeding up the gas-phase conversion of large molecules while lessening possible memory effects. The liner is easily replaceable for a quick and extremely simple interface maintenance. Proof of concept and detailed description of the interface are here presented.