Detection of trace levels of lead in aqueous liquids using extractive electrospray ionization tandem mass spectrometry

Extractive electrospray ionization mass spectrometry for analytical evaluation and synthetic preparation of pharmaceutical chemicals

Extraction electrospray ionization mass spectrometry (EESI-MS), due to the unique configuration of its ionization module, enables the effective ionization of trace molecules of interest in samples containing complex matrices with high sensitivity, high selectivity and high responding speed without requiring sample pretreatment, and allows high-energy molecular species to undergo specially designed reactions for advanced functionalization. The typical effects of operating conditions on the analytical performance of extraction electrospray ionization mass spectrometry for various pharmaceutical compounds, pharmaceutical preparations and herbal materials were systematically reviewed. The application prospect of extraction electrospray ionization in molecular functionalization for advanced drug discovery is also briefly introduced.

Real-Time Detection of Aerosol Metals Using Online Extractive Electrospray Ionization Mass Spectrometry

Metal emissions are of major environmental and practical concern because of their highly toxic effects on human health and ecosystems. Current technologies available in the market for their detection are typically limited by a time resolution of 1 h or longer (e.g., via semicontinuous X-ray fluorescence measurements) or are nonquantitative (e.g., laser ablation mass spectrometry). In this work, we report the development of a novel technique for the real-time detection and monitoring of metal particles in situ using an extractive electrospray ionization (EESI) source coupled to a high-resolution time-of-flight mass spectrometer (TOF-MS). The experiments were conducted in negative ionization mode using disodium ethylenediamine tetraacetic acid (EDTA) dihydrate to chelate with metals and form stable metal complexes. Results for water-soluble metal compounds were obtained. The following representative metal ions were examined: Pb, Cd, Zn, Ce (III), Ba, Ni, Fe(II), Fe(III), Cu(II), Cr, Mo, Co(II), Mg, Nd, Li, Ti, Ca, Cs, Ag, Tm, Er(III), La(III), Yb(III), Eu(III), Pr(III), Gd(III), Lu(III), Dy(III), Tb(III), Ho, and Ru(III). The results showed a very good linear mass response (R² = 0.9983), low ng/m³ limits of detection (LoD), and a fast response time (1 s). The stability and repeatability of the developed EESI-TOF-MS were tested under complex dynamic and periodic experimental conditions, and negligible matrix effects were measured for internally and externally mixed metal particles. Benchmark testing against inductively coupled plasma-mass spectrometry (ICP-MS) was also performed, highlighting the online measurement capabilities of aerosol metals with a LoD lower than those of ICP-MS. Proof-of-concept ambient measurements were performed in New Delhi, India, and very promising results were obtained, allowing further exploitation elsewhere.

Identification of complexes involving thallium(I) and thallium(III) with EDTA and DTPA ligands by electrospray ionization mass spectrometry

RATIONALE

Thallium is considered to be an environmental threat; however, its hazardous properties depend on its oxidation state. Tl(III) is approx. 1000-times more toxic compared with Tl(I), therefore identification of each species is essential in order to properly evaluate the associated health hazard. Electrospray ionization mass spectrometry (ESI-MS) allows determination of speciation in solution due to its soft mode of ionization while selective complexation with ligands can distinguish the Tl species. Selective complexation of Tl(I) and Tl(III) ions requires the use of two selective complexing agents and selection of appropriate conditions for this process.

METHODS

Tl(I) and Tl(III) ions as well as two ligands (EDTA and DTPA) were used to form binary (single ion + single ligand), ternary (one ion + both ligands) and quaternary systems (both ions and both ligands) under different pH conditions (7 and 8). These mixtures were subjected to the determination of Tl species using ESI-MS operating in positive and negative ion mode.

RESULTS

Tl(I) complexes with DTPA were identified at pH 7 and 8, whereas, in the case of EDTA, the complexes were detected only at pH 8. In contrast, Tl(III) formed distinct complexes with EDTA at pH 7 and 8, while with DTPA the complexes were detected only at pH 8. Analysis of the quaternary system (which contained both ions and both ligands) revealed that Tl(I) formed complexes with EDTA, while Tl(III) formed complexes with DTPA at pH 7 and 8.

CONCLUSIONS

The obtained results confirmed that the increase in the solution complexity allowed simultaneous identification of different complexes in solutions containing both Tl species. The initial analyses carried out for binary and ternary solutions facilitated the simultaneous determination of specific complexes (Tl(I) with EDTA and Tl(III) with DTPA) in the quaternary system.

Determination of elemental composition of metals using ambient organic mass spectrometry

Conventional inorganic mass spectrometric (MS) analysis of metals can require time-consuming and tedious sample preparation. We thus report the novel and direct characterization of metals in solid samples using an organic MS technique known as electrospray laser desorption ionization mass spectrometry (ELDI/MS). No sample pretreatment was needed, and results were rapidly obtained due to the ambient and laser-based nature of ELDI/MS. Metals from samples were desorbed and ionized by laser irradiation, after which they reacted with EDTA and then post-ionized and detected as metal-EDTA complexes. Aluminum, copper, iron, lead, nickel, and zinc from plates, foils, and coins were characterized in seconds. This study demonstrates that an ESI/MS system can be easily modified to analyze metal elements in solids by involving a chelating agent, indicating a potentially promising development in MS towards the analysis of metals using organic MS.

Applications of DART-MS for food quality and safety assurance in food supply chain

Direct analysis in real time (DART) represents a new generation of ion source which is used for rapid ionization of small molecules under ambient conditions. The combination of DART and various mass spectrometers allows analyzing multiple food samples with simple or no sample treatment, or in conjunction with prevailing protocolized sample preparation methods. Abundant applications by DART-MS have been reviewed in this paper. The DART-MS strategy applied to food supply chain (FSC), including production, processing, and storage and transportation, provides a comprehensive solution to various food components, contaminants, authenticity, and traceability. Additionally, typical applications available in food analysis by other ambient ionization mass spectrometers were summarized, and fundamentals mainly including mechanisms, devices, and parameters were discussed as well. © 2015 Wiley Periodicals, Inc. Mass Spec Rev. 36:161-187, 2017.

A microwave plasma torch quadrupole mass spectrometer for monitoring trace levels of lead and cadmium in water

RATIONALE

The microwave plasma torch (MPT) is a low power-consumption and easily operated plasma generator. As an ambient ion source, the MPT can be coupled with various mass spectrometers and applied in real-time analysis of metal elements in water for the demands of environmental control and water quality inspection.

METHODS

We constructed a quadrupole mass spectrometer with an MPT as the ion source to detect directly trace levels of lead and cadmium in water. Without any pretreatments,water samples were first pneumatically nebulized with a desolvation unit, then flowed through the central tube of the MPT and finally entered the plasma. After that, the metal ions produced were introduced into the mass spectrometer to be analyzed via an atmospheric inlet of a stainless steel capillary tube.

RESULTS

The MPT mass spectra of lead and cadmium ions were characterized with clear unit isotopic resolution. The sensitivity reached levels of 20 ng/L for lead and 72.7 ng/L for cadmium in water, respectively. The linear response range covered at least 2 orders of magnitude. Moreover, a single aqueous sample could be completely analyzed within 3 minutes, providing reasonably relative standard deviation values.

CONCLUSIONS

Our results demonstrated that this MPT mass spectrometer is a useful tool for the monitoring of lead and cadmium ions in water, which makes it a potential alternative to ICP-MS, to be used in the fields of environmental control and water quality and foodstuff safety inspection. Copyright © 2016 John Wiley & Sons, Ltd.

The cation−anion interaction in ionic liquids studied by extractive electrospray ionization mass spectrometry

Ionic liquids, known as green solvents, are of sustainable interest in modern chemistry, industry, and many other fields. Here, extractive electrospray ionization has been applied to transfer various room temperature ionic liquids into the gas phase for mass spectrometry analysis. Generated mass spectra display free cations (C+), anions (A–), and small salt clusters, such as C2A+ and CA2–, from strongly diluted ionic liquid samples (<10−8 mol/L) with high sensitivity and tolerance to chemical contamination. The eight ionic liquids based on the 1-butyl-3-methylimidazolium cation with different anions (OH–, HSO4–, Cl–, BF4–, AlCl4–, NO3–, Ac–, and PF6–) are investigated in the present work. Interestingly, the 1-butyl-3-methylimidazolium cation signal intensity is inversely correlated with the hydrogen bonding strength between the anion and cation. Our study indicates that the direct extractive electrospray ionization mass spectrometry analysis is a convenient method to screen ionic liquid libraries with regard to chemical composition, physicochemical properties, and supramolecular organization of ionic liquids.