About the Electrospray Ionization Source in Mass Spectrometry: Electrochemistry and On-chip Reactions

The present work shows that the electrochemical properties of electrospray ionization (ESI) can be used to add functions to the process. As example, we show how the choice of the electrode material can be used to study interactions between metal ions and biomolecules in mass spectrometry (MS). In positive ionization MS, an electrospray device acts as anode, which implies oxidation reactions. Sacrificial electrodes (made of copper or zinc) are used to supply the electrospray current and to produce cations that are able to react on-line with compounds of interest. Thus, the interactions between copper ions and ligands or peptides were investigated by using a copper electrode. Another example is the in situ electrogeneration of a dinuclear zinc(II) complex for the mass tagging of phosphopeptides when working with a zinc electrode. In order to perform these reactions on the same microchip, a dual-channel microsprayer was used, where one channel was dedicated to the tag electrogeneration and the other to the infusion of a phosphopeptides solution. Finally, this dual-channel microsprayer was used to study complexation at liquid-liquid interfaces in biphasic ESI-MS, such as thioether crowns and lead ions or peptides and phospholipids complexes. These examples illustrate the use of electrochemistry and on-chip reactions in ESI-MS analysis

Electrochemical Sensor Research at the Laboratoire d'Electrochimie of the EPFL

This review presents some recent developments in the field of electroanalytical sensors. We first explain the working principle of electrochemistry at the interface between two immiscible electrolyte solutions (ITIES), illustrated by the example of copper transferring through a water/1,2-dichloroethane interface when the ionophore 1,4,7,10-tetrathiacyclododecane is present in the organic phase. The obtained results show that assisted ion-transfer reactions take place with both CuI and CuII, but that the interfacial process is complicated by the fact that CuI disproportionates in water and that CuII can be reduced in the organic phase.Based on the same experimental methodology, a new type of amperometric detector for non-redox ions has been developed using a composite polymer membrane supporting a gelified organic phase that can incorporate an ionophore such as valinomycin. We report here the use of a (o-nitrophenyloctylether)-(poy(vinyl chloride) (NPOE-PVC) gel micro-interface as a detector for cations and anions in ion-exchange chromatography. The main advantage of this approach is that selectivity and sensitivity can be tailored by the choice of the ionophore and by the polarisation potential.This ion detector has also been incorporated in a miniaturised total-analysis system (µ-TAS) fabricated in a polymer sheet by UV-laser photoablation. This microfabrication technique is used for the prototyping of a disposable capillary-electrophoresis microsystem comprising on-chip injector, separation column and electrochemical detector. This system is further used with built-in carbon-ink electrodes for the detection of electroactive species. These microsystems are now under development for immuno-sensor applications

Locally Grown, Natural Ingredients? The Isotope Ratio Can Reveal a Lot!

This communication gives an overview of selected isotope analyses applied to food authenticity assessment. Different isotope ratio detection technologies such as isotope ratio mass spectrometry (IRMS) and cavity ring down spectroscopy (CRDS) are briefly described. It will be explained how ?18O of water contained in fruits and vegetables can be used to assess their country of production. It will be explained why asparagus grown in Valais, in the centre of the Alps carries much less heavy water than asparagus grown closer to the sea coast. On the other hand, the use of ?13C can reveal whether a product is natural or adulterated. Applications including honey or sparkling wine adulteration detection will be briefly presented

Use of Isotope Ratio Determination (13C/12C) to Assess the Production Method of Sparkling Wine

The production of a sparkling wine can be performed with different methods taking from a few weeks to several years, which often justifies a difference in added value for the consumer. This paper presents the use of isotope ratio ?13C measurements combined with physico-chemical analyses for the determination of mislabelling of sparkling wines produced by 'ancestral', 'traditional', 'closed tank' or 'gasification' methods. This work shows that the isotope composition of CO2 compared with that of the corresponding dried residue of wine (DRW) can assess whether carbonate CO2 in a sparkling wine originates from alcohol fermentation or from artificial gas addition. Isotopic ratios expressed as ?13CCO2 and ?13CDRW measurements have been obtained for each wine by gasbench isotopic ratio mass spectroscopy and cavity ring down infrared spectroscopy, respectively. When the difference between ?13CCO2 and ?13CDRW is negative, the presence of artificial CO2 can be undoubtedly inferred, which would exclude the production methods 'ancestral' or 'traditional' for instance. Other parameters such as alcohol content, sugar and acid distributions are also important to complete the analytical panel to aid fraud tracking

Use of Isotope Ratio Mass Spectrometry (IRMS) Determination (18O/16O) to Assess the Local Origin of Fish and Asparagus in Western Switzerland

Here we present the use of isotope ratio mass spectrometry (IRMS) for the detection of mislabelling of food produced in Switzerland. The system is based on the analysis of the oxygen isotope distribution in water (?18O). Depending on the location on the earth, lake or groundwater has a specific isotopic distribution, which can serve as a fingerprint in order to verify whether a product has grown by means of the corresponding water. This report presents specifically the IRMS technique and the results obtained in the origin detection of fish grown in selected Swiss lakes as well as asparagus grown in Valais ground. Strengths and limitations of the method are presented for both cited products; on one hand, the technique is relatively universal for any product which contains significant water but on the other hand, it necessitates a rather heavy workload to build up a database of water ?18O values of products of different origins. This analytical tool is part of the concept of combating fraud currently in use in Switzerland

Multi-track single- and dual-channel plastic microchips for electrospray mass spectrometry

Disposable plastic electrospray chips are particularly attractive for the automated analysis of organic compounds and organometallic compounds. Automated multi-track chip-based infusion electrospray mass spectrometry of low molecular weight compounds using an eight-channel plastic chip is presented. For that purpose, the commercial interface of a triple quadrupole linear ion trap was modified. A dual-channel plastic microchip, where two physically separated channels arrive very close to each other at the chip tip, was used to perform lock-mass accurate mass measurements on a quadrupole-time-of-flight instrument. The same chip was used to demonstrate the formation of an organometallic complex in solution on the chip tip. Furthermore, the potential to control the flow rate of each channel individually, which opens new possibilities in the study of supramolecular complexes, is discussed