Analytica Chimica Acta (v.824, #C)

Solid-state gas sensors for breath analysis: A review by Corrado Di Natale; Roberto Paolesse; Eugenio Martinelli; Rosamaria Capuano (1-17).
Display OmittedThe analysis of volatile compounds is an efficient method to appraise information about the chemical composition of liquids and solids. This principle is applied to several practical applications, such as food analysis where many important features (e.g. freshness) can be directly inferred from the analysis of volatile compounds.The same approach can also be applied to a human body where the volatile compounds, collected from the skin, the breath or in the headspace of fluids, might contain information that could be used to diagnose several kinds of diseases. In particular, breath is widely studied and many diseases can be potentially detected from breath analysis.The most fascinating property of breath analysis is the non-invasiveness of the sample collection. Solid-state sensors are considered the natural complement to breath analysis, matching the non-invasiveness with typical sensor features such as low-cost, easiness of use, portability, and the integration with the information networks. Sensors based breath analysis is then expected to dramatically extend the diagnostic capabilities enabling the screening of large populations for the early diagnosis of pathologies.In the last years there has been an increased attention to the development of sensors specifically aimed to this purpose. These investigations involve both specific sensors designed to detect individual compounds and non-specific sensors, operated in array configurations, aimed at clustering subjects according to their health conditions. In this paper, the recent significant applications of these sensors to breath analysis are reviewed and discussed.
Keywords: Gas sensors; Sensor arrays; Breath analysis; Medical diagnosis;

Modern analytical supercritical fluid chromatography using columns packed with sub-2 μm particles: A tutorial by Lucie Nováková; Alexandre Grand-Guillaume Perrenoud; Isabelle Francois; Caroline West; Eric Lesellier; Davy Guillarme (18-35).
Display OmittedThis tutorial provides an overview of the possibilities, limitations and analytical conditions of modern analytical supercritical fluid chromatography (SFC) using columns packed with sub-2 μm particles. In particular, it gives a detailed overview of commercially available modern SFC instrumentation and the detectors that can be employed (UV, MS, ELSD, FID, etc.). Some advice on the choice of the stationary phase dimensions and chemistries, the nature of the mobile phase (choice of organic modifier and additives) and its flow rate as well as the backpressure and temperature are also provided. Finally, several groups of potentially problematic compounds, including lipophilic compounds, hydrophilic substances and basic drugs, are discussed in detail. All these families of analytes can be resolved with SFC but require specific analytical conditions.
Keywords: Supercritical fluid chromatography; Ultra-high performance supercritical fluid chromatography; Sub-2 μm particles; Mobile phase selection; Column selection; Tutorial;

Display OmittedQuadruple isotope dilution mass spectrometry (ID4MS) has been applied for simultaneous determination of nitrite and nitrate in seawater. ID4MS allows high-precision measurements and entails the use of isotopic internal standards (18O-nitrite and 15N-nitrate). We include a tutorial on ID4MS outlining optimal experimental design which generates results with low uncertainties and obviates the need for direct (separate) evaluation of the procedural blank. Nitrite and nitrate detection was achieved using a headspace GCMS procedure based on single-step aqueous derivatization with triethyloxonium tetrafluoroborate at room temperature. In this paper the sample preparation was revised and fundamental aspects of this chemistry are presented. The proposed method has detection limits in the low parts-per-billion for both analytes, is reliable, precise, and has been validated using a seawater certified reference material (MOOS-2). Simplicity of the experimental design, low detection limits, and the use of quadruple isotope dilution makes the present method superior to the state-of-the-art for determination of nitrite and nitrate, and an ideal candidate for reference measurements of these analytes in seawater.
Keywords: Quadruple isotope dilution; High-precision; Nitrite and nitrate; Seawater; Triethyloxonium tetrafluoroborate derivatization; GCMS;

Multi-response optimization of the extraction and derivatization protocol of selected polar metabolites from apple fruit tissue for GC–MS analysis by Elias A. Bekele; Carlo E.P. Annaratone; Maarten L.A.T.M. Hertog; Bart M. Nicolai; Annemie H. Geeraerd (42-56).
Display OmittedGiven the complexity of the plant metabolome exhibiting a wide spectrum of physico-chemical properties, finding the best compromise for GC–MS analysis is a challenging exercise. In this study, the GC–MS protocol for extracting and analyzing polar metabolites from apple tissue is optimized. We found pure methanol extraction to be slightly better as compared to the two phase methanol/chloroform/water extraction in terms of introducing less degradation of the extracted metabolites while being comparable in extraction efficiency and repeatability. The methanol extraction was superior to the single phase methanol/chloroform/water extraction in all performance measures. A multi-response optimization based on a desirability function was applied to optimize the derivatization. This procedure allows searching for optimal parameters while simultaneously considering overall detection enhancement of metabolites from various metabolic classes. A short oximation at a high temperature in combination with a low silylation temperature gave results similar to a longer oximation at low temperature in combination with a high silylation temperature. Increasing silylation time from 0.5 h to 2 h resulted in an improvement of the silylation reaction.
Keywords: Apple; Derivatization; Design of experiment; Gas chromatography–mass spectrometry; Metabolomics; Multi-response optimization;

Display OmittedA sensitive electrochemiluminescence (ECL) sensor for melamine analysis was fabricated based on Ru(bpy)3 2+-doped silica (Ru(bpy)3 2+@SiO2) nanoparticles and graphene composite. Spherical Ru(bpy)3 2+@SiO2 nanoparticles with uniform size about 55 nm were prepared by the reverse microemulsion method. Since per Ru(bpy)3 2+@SiO2 nanoparticle encapsulated a great deal of Ru(bpy)3 2+, the ECL intensity has been greatly enhanced, which resulted in high sensitivity. Due to its extraordinary electric conductivity, graphene improved the conductivity and accelerated the electron transfer rate. In addition, graphene could work as electronic channel improving the efficient luminophor amount participating in the ECL reaction, which further enhanced the ECL signal. This proposed sensor was used to melamine analysis and the ECL intensity was proportional to logarithmic melamine concentration range from 1 × 10−13  M to 1 × 10−8  M with the detect limit as low as 1 × 10−13  M. In application to detect melamine in milk, satisfactory recoveries could be obtained, which indicated this sensor having potential application in melamine analysis in real samples.
Keywords: Electrochemiluminescence; Ru(bpy)3 2+-doped silica; Graphene; Melamine;

Mimicking Daphnia magna bioassay performance by an electronic tongue for urban water quality control by Dmitry Kirsanov; Evgeny Legin; Anatoly Zagrebin; Natalia Ignatieva; Vladimir Rybakin; Andrey Legin (64-70).
Display OmittedToxicity is one of the key parameters of water quality in environmental monitoring. However, being evaluated as a response of living beings (as their mobility, fertility, death rate, etc.) to water quality, toxicity can only be assessed with the help of these living beings. This imposes certain restrictions on toxicity bioassay as an analytical method: biotest organisms must be properly bred, fed and kept under strictly regulated conditions and duration of tests can be quite long (up to several days), thus making the whole procedure the prerogative of the limited number of highly specialized laboratories. This report describes an original application of potentiometric multisensor system (electronic tongue) when the set of electrochemical sensors was calibrated against Daphnia magna death rate in order to perform toxicity assessment of urban waters without immediate involvement of living creatures. PRM (partial robust M) and PLS (projections on latent structures) regression models based on the data from this multisensor system allowed for prediction of toxicity of unknown water samples in terms of biotests but in the fast and simple instrumental way. Typical errors of water toxicity predictions were below 20% in terms of Daphnia death rate which can be considered as a good result taking into account the complexity of the task.
Keywords: Bioassay; Water toxicity; Multisensor systems; Electronic tongue;

Ratiometric near-infrared chemosensor for trivalent chromium ion based on tricarboyanine in living cells by Chun-Yan Li; Xue-Fei Kong; Yong-Fei Li; Chao Weng; Jia-Liang Tang; Dan Liu; Wei-Guo Zhu (71-77).
Display OmittedA tricarboyanine derivative (IRPP) is applied as a ratiometric near-infrared chemosensor for detecting trivalent chromium ions (Cr3+) in living cells. Upon the addition of Cr3+ to a solution of IRPP, large-scale shifts in the emission spectrum (from 755 nm to 561 nm) are observed. In the newly developed sensing system, these well-resolved emission peaks yield a sensing system that covers a linear range from 1.0 × 10−7 to 1.0 × 10−5  M with a detection limit of 2.5 × 10−8  M. The experimental results show the response behavior of IRPP towards Cr3+ is pH independent under neutral conditions (6.0–7.5). Most importantly, the fast response time (less than 3 min) and selectivity for Cr3+ over other common metal ions provide a strong argument for the use of this sensor in real world applications. As a proof of concept, the proposed chemosensor has been used to detect and quantify Cr3+ in river water samples and to image Cr3+ in living cells with encouraging results.
Keywords: Chemosensor; Ratiometric; Near-infrared; Tricarboyanine; Chromium ion;