Flow Injection Analyses Research Articles

Determination of mefenamic acid in aqueous solutions using merging zone – continuous flow injection

AbstractThis research aims at using a novel algorithm to determine the concentration of mefenamic acid (MA) in solutions using merging zone-continuous flow injection. The MA concentration in aqueous solutions was determined using this technology, and the results obtained using this method were compared to those obtained using more conventional methods. All flow injection analyses were carried out utilizing a Rheodyne valve 7725, a Rabbit peristaltic pump, a BioLogic QuadTec UV-Vis Detector, and a Sartorius CPA2P Competence Analytical Balance, as well as a Sartorius CPA2P Competence Analytical Balance. The data is then received by a signal detector and a specialized software spectrometer. A spectroscopic scan is used to determine the maximum wavelength of the product, a calibration curve is created, and measurements are taken to estimate the drug's absolute concentrations in aqueous solutions. The detection and quantitative limits were set to 0.021 and 0.071 parts per million. This treatment is popular and could be a good alternative to conventional methods because it is simple, rapid, precise, inexpensive, and adaptable.

Towards a Comprehensive Characterization of the Low-Temperature Autoxidation of Di-n-Butyl Ether.

In the present study, we investigated the oxidation of 2500 ppm of di-n-butyl ether under fuel-rich conditions (φ = 2) at low temperatures (460–780 K), a residence time of 1 s, and 10 atm. The experiments were carried out in a fused silica jet-stirred reactor. Oxidation products were identified and quantified in gas samples by gas chromatography and Fourier transform infrared spectrometry. Samples were also trapped through bubbling in cool acetonitrile for high-pressure liquid chromatography (HPLC) analyses. 2,4-dinitro-phenylhydrazine was used to derivatize carbonyl products and distinguish them from other isomers. HPLC coupled to high resolution mass spectrometry (Orbitrap Q-Exactive®) allowed for the detection of oxygenated species never observed before, i.e., low-temperature oxidation products (C8H12O4,6, C8H16O3,5,7, and C8H18O2,5) and species that are more specific products of atmospheric oxidation, i.e., C16H34O4, C11H24O3, C11H22O3, and C10H22O3. Flow injection analyses indicated the presence of high molecular weight oxygenated products (m/z > 550). These results highlight the strong similitude in terms of classes of oxidation products of combustion and atmospheric oxidation, and through autoxidation processes. A kinetic modeling of the present experiments indicated some discrepancies with the present data.

Experimental and kinetic modeling study of n-hexane oxidation. Detection of complex low-temperature products using high-resolution mass spectrometry

This study concerns the oxidation of n-hexane. It was conducted in continuous flow fused-silica jet-stirred reactor (JSR) at 10 atm and an equivalence ratio of 0.5. n-Hexane initial concentrations were (i) 2500 ppm with a mean residence time of 1.5 s and (ii) 1000 ppm with a mean residence time of 0.7 s; we operated in the cool-flame regime for temperatures ranging from 540 to 720 K and 530 to 800 K, respectively. Products were analyzed and quantified in the gas phase using gas chromatography (with flame ionization, thermal conductivity, and quadrupole mass spectrometry) and Fourier transform infrared spectrometry. Products of low-temperature oxidation were sampled in the JSR and trapped in acetonitrile for characterization using an Orbitrap Q-Exactive®. Flow injection analyses (FIA) and ultra-high pressure liquid chromatography (UHPLC) coupled with atmospheric pressure chemical ionization (APCI +/- modes)- high resolution mass spectrometry (HRMS) analyses were used to characterize hydroperoxides (C6H14O2), keto-hydroperoxides (C6H12O3, C3H6O3, C4H8O3, and C5H10O3), cyclic ethers (C6H12O), carboxylic acids (C2 to C6), ketones (C3 to C6), diones (C6H10O2), unsaturated ketones (C6H10O and C6H8O), unsaturated diones (C6H8O2), and highly oxygenated molecules (C6H12O4-8) produced by addition of three and four oxygen molecules on fuel's radicals. To confirm the presence of hydroxyl or hydroperoxyl groups in the oxidation products we used H/D exchange with D2O. 2,4-Dinitrophenylhydrazine (2,4-DNPH) derivatization was used to characterize and confirm the presence of different carbonyls which can be formed during the low temperature oxidation of n-hexane. An available kinetic reaction mechanism including 3rd O2 addition on fuel's radicals was used to simulate the formation of the presently detected keto-hydroperoxides (KHP) and highly oxygenated molecules (HOMs).

Oxidation of diethyl ether: Extensive characterization of products formed at low temperature using high resolution mass spectrometry

The oxidation of a stoichiometric diethyl ether-oxygen-nitrogen mixture containing 5000 ppm of fuel was studied in a jet-stirred reactor at 10 atm and a residence times of 1 s. Experimental temperatures varied stepwise for 440 to 740 K and products were quantified by gas chromatography with TCD and FID, gas chromatography-mass spectrometry, and FTIR. Other experiments in the temperature range 480 to 570 K were performed for characterizing elusive cool flame products. To this end, gas samples were trapped in acetonitrile for flow injection analyses and liquid chromatography-mass spectrometry (Orbitrap Q-ExactiveⓇ). For ionization, we used positive and negative atmospheric pressure chemical ionization (APCI). Among fuel-specific products, hydroperoxides and diols (C4H10O3), carbonyl hydroperoxides (C4H8O4), acetic acid, di-keto ethers (C4H6O3), cyclic ethers (C4H8O2) and highly oxygenated molecules, i.e., keto-dihydroperoxides (C4H8O6), keto-trihydroperoxides (C4H8O8), di-keto-hydroperoxides (C4H6O5), and diketo-dihydroperoxides (C4H6O7), were detected. To confirm the presence of –OH or –OOH groups in oxidation products, H/D exchange with D2O was used. DNPH derivatization was used to identify carbonyls present in samples, especially those with a molecular weight below 50 amu which cannot be detected directly by the mass spectrometer. Chemical kinetic modeling using a mechanism taken from the literature was performed. Although reasonable agreement between the data and the simulations was observed for several species, some discrepancies between experimental and computed mole fractions were observed.

Low-temperature oxidation of a gasoline surrogate: Experimental investigation in JSR and RCM using high-resolution mass spectrometry

The oxidation of a gasoline model-fuel (2500 ppm of n-heptane and 2500 ppm of isooctane), called RON 50, was studied in a jet-stirred reactor (JSR) over the temperature range 560 ‒ 700 K, at a total pressure of 10 atm, at a residence time of 1.5 s, and an equivalence ratio of 0.5. Gas samples were collected as a function temperature. Ignition of RON 50/air mixtures was also studied in a rapid compression machine (RCM) under the same fuel-lean conditions, 20 bar, 640 K. Gas samples were collected at variable reaction time. Products of low-T oxidation formed in a jet-stirred reactor and a rapid compression machine were dissolved in acetonitrile and analyzed by high-resolution mass spectrometry. Flow injection analyses and ultrahigh-pressure liquid chromatography coupled to an OrbitrapⓇ were used to characterize a wide range of species such as hydroperoxides, diols, ketohydroperoxides, carboxylic acids, diketones, cyclic ethers (CnH2nO) formed by decomposition of alkyl hydroperoxy radicals, and highly oxidized species formed via up to six O2 additions on alkyl radicals (CnH2nO11). Mass spectrometry analyses were conducted using atmospheric pressure chemical ionization running in negative and positive ionization modes. For confirming the presence of –OH or –OOH groups in the products, we performed H/D exchange by addition of D2O to samples. Under JSR conditions, we observed a wide range of n-heptane oxidation products: C7H14Ox (x = 1‒11), C7H12Ox (x = 1‒11), C7H10Ox (x = 1‒9), C7H8Ox (x = 1‒9), C7H6Ox (x = 1‒8), and C7H4Ox (x = 1‒6). Similarly, the following products of isooctane oxidation were observed: C8H16Ox (x = 1‒12), C8H14Ox (x = 1‒11), C8H12Ox (x = 1‒12), C8H10Ox (x = 2‒10), C8H8Ox (x = 2‒8), C8H6Ox (x = 1‒7). Finally, CnH2n (n = 4‒8), CnH2n-2 (n = 4‒8), CnH2nO (n = 3‒8), CnH2n-2O (n = 3‒8), CnH2n-4O (n = 3‒8), CnH2n+2O2 (n = 3‒8), CnH2nO2 (n = 2‒8), CnH2n-2O2 (n = 3‒8), CnH2n-4O2 (n = 3‒8), and CnH2nO3 (n = 2‒8) were also observed. Most of these products were also detected in RCM samples. Products measurements indicated that RON 50 oxidation routes are similar under RCM and JSR experimental conditions. A kinetic reaction mechanism was used to compare the formation of products versus temperature in a JSR. New pathways need to be introduced in existing reaction schemes for predicting newly detected cool-flame products.

Development of an electrochemical sensor based on carbon black for the detection of cannabidiol in vegetable extracts.

A glassy carbon electrode chemically modified with a carbon black coating is proposed here for the rapid and portable determination of cannabidiol (CBD) in a commercial Cannabis seed oil and in fibre-type Cannabis sativa L. leaves. The mechanism of CBD oxidation was studied in relation to simpler phenyl derivatives bearing the same electroactive group, namely resorcinol and 2-methylresorcinol. These molecules also allowed us to determine the best conditions for the electrochemical detection of CBD, as to the pH value and to the best solvent mixture to use. Carbon black was chosen among nanostructured carbon-based materials owing to its outstanding features as an electrode modifier for analyte detection. The performance of the modified electrode was determined by flow injection analyses of standard solutions of CBD, obtaining a linear correlation between the oxidation current and the analyte concentration; the sensor response is characterised by suitable repeatability and reproducibility. The analysis of commercial products by the standard addition method allowed us to ascertain the accuracy of the sensor for the detection of CBD in real samples.

Experimental Characterization of Tetrahydrofuran Low-Temperature Oxidation Products Including Ketohydroperoxides and Highly Oxygenated Molecules

The oxidation of tetrahydrofuran (THF) was carried out in a continuously jet-stirred tank reactor (JSR) at a total pressure of 10 atm, in fuel-lean conditions (equivalence ratio = 0.5), an initial fuel mole fraction of 5000 ppm, at a mean residence time of 2 s, and for temperatures ranging from 550 to 620 K. High-resolution mass spectrometry analyses was used to characterize low-temperature oxidation products of THF. MS analyses were performed using atmospheric pressure chemical ionizations in positive and negative modes. Both flow injection analyses and ultra-high-pressure liquid chromatography-MS/MS allowed characterizing a large set of chemicals including hydroperoxides and diols (C 4 H 8 O 3), ketohydroperoxides (C 4 H 6 O 4), and more oxygenated molecules (up to C 4 H 8 O 7) resulting from up to three oxygen molecules addition of on α and β THF radicals. The existence of-OH or-OOH groups in the products was confirmed by hydrogen-deuterium exchange using D 2 O. We detected 24 products with molecular weight of 40-168, not reported in previous studies. Simulations using the latest THF oxidation chemical kinetic reaction mechanism available from the literature were compared to the present measurements of ketohydroperoxides and other products of THF cool flame. The kinetic scheme represented well the present qualitative data.

High-defined quantitative snapshots of the ganglioside lipidome using high resolution ion mobility SLIM assisted shotgun lipidomics

Defects in sphingolipid metabolism have emerged as a common link across neurodegenerative disorders, and a deeper understanding of the lipid content in preclinical models and patient specimens offers opportunities for development of new therapeutic targets and biomarkers. Sphingolipid metabolic pathways include the formation of glycosphingolipid species that branch into staggeringly complex structural heterogeneity within the globoside and ganglioside sub-lipidomes. Characterization of these sub-lipidomes has typically relied on liquid chromatography-mass spectrometry-based (LC-MS) approaches, but such assays are challenging and resource intensive due to the close structural heterogeneity, the presence of isobaric and isomeric species, and broad dynamic range of endogenous glycosphingolipids. Here, we apply Structures for Lossless Ion Manipulations (SLIM)-based High Resolution Ion Mobility (HRIM)-MS to enable rapid, repeatable, quantitative assays with deep structural information sufficient to resolve endogenous brain gangliosides at the level of individual molecular species. Analyses were performed using a prototype SLIM-MS instrument equipped with a 13-m serpentine path which enabled resolution of closely related isomeric analytes such as GD1a d36:1 and GD1b d36:1 based on recorded mass-to-charge (m/z) and arrival times. To demonstrate the power of our methodology, brain extracts derived from wild-type mice hemi-brains were analyzed by HRIM-MS using flow injection analyses (FIA) without the need for additional separation by liquid chromatography. Endogenous ganglioside species were readily resolved, identified, and quantified by FIA-SLIM-MS analyses within 2 min per sample. Thus, the FIA-SLIM-MS platform enables robust quantification across a broad range of lipid species in biological specimens in a standardized assay format that is readily scalable to support studies with large sample numbers.

Experimental characterization of n-heptane low-temperature oxidation products including keto-hydroperoxides and highly oxygenated organic molecules (HOMs)

The oxidation of n-heptane was performed in a jet-stirred reactor (JSR) at 10 atm, an equivalence ratio of 0.5, and an initial fuel concentration of 1000 ppm at a residence time of 1 s in the temperature range 580–790 K (from cool-flame, negative temperature coefficient NTC, to intermediate temperature oxidation regime), and with 5000 ppm of fuel at 647 K and a residence time of 1.5 s. Low-temperature products formed in JSR were characterized using high-resolution mass spectrometry analyses (HRMS). Atmospheric pressure chemical ionizations (APCI) was used in positive and negative modes for MS analyses. Both flow injection analyses (FIA) or ultra-high-pressure liquid chromatography-OrbitrapⓇ coupling were used to characterize hydroperoxides (C7H16O2), keto-hydroperoxides (C7H14O3), cyclic ethers (C7H14O), carboxylic acids (C2H4O2, C3H6O2, C4H8O2), ketones (C3–5H6–10O), diones (C7H12O2), and highly oxygenated molecules (C7H14O5, C7H14O7, C7H14O9, C7H14O11) resulting from the addition of up to six O2 molecules on fuel radicals. H/D exchange with D2O was used to confirm the presence of –OH or –OOH groups in the products. Several available kinetic reaction mechanisms were tested against the present measurements of keto-hydroperoxides showing significant discrepancies.

Oxidation of di-n-butyl ether: Experimental characterization of low-temperature products in JSR and RCM

The oxidation of di-n-butyl-ether (DBE) was performed in a jet-stirred reactor (JSR) at 1 atm, 520 and 530 K, and from 480 to 670 K at 10 atm, at a residence time of 1 s, an equivalence ratio of 0.5, and an initial fuel concentration of 5000 ppm. Ignition experiments on DBE/air mixtures were also performed in a rapid compression machine (RCM) under stoichiometric conditions, 5 bar, and from 550 to 630 K. Low-temperature products formed in JSR and RCM experiments were characterized. To this end, high-resolution mass spectrometry analyses (HRMS) with flow injection analyses or ultra-high pressure liquid chromatography coupling were used to characterize hydroperoxides and diols (C8H18O3), ketohydroperoxides (C8H16O4), carboxylic acids (C2H4O2, C3H6O2, C4H8O2), di-keto ethers (C8H14O3), and highly oxygenated molecules (C8H14O5, C8H16O6, C8H14O6, C8H14O7, C8H16O8, and C8H14O9) resulting from up to five O2 additions on fuel's radicals. Whereas HOMs are of minor importance in combustion, they are considered key species for the formation of secondary organic aerosols. In addition, cyclic ethers and esters (C8H16O2) were observed. Heated electrospray and atmospheric pressure chemical ionizations (HESI and APCI) were used in positive and negative modes for MS analyses. H/D exchange with D2O was used to confirm the presence of –OH or –OOH groups in the products. The present results show that DBE oxidation proceeds similarly under JSR and RCM conditions. Whereas the CH2 groups neighboring the ether group are the most favorable sites for H-atom abstraction reactions, speciation indicated that other sites can react by metathesis forming a large pool of intermediates and products. Our kinetic reaction mechanism needs to be extended for simulating the formation of newly detected species.

Phosphomolybdenum Blue Detection – A Review of Characteristics, Achievements, Challenges and Future Prospects

Phosphate detection in the environment (especially, water bodies) is very essential in view of its consequent pollution effects on eutrophication. Continuous monitoring of phosphate concentration (and phosphorus compounds in general) in water samples has been based on phosphomolybdenum blue formation coupled with spectrophotometric detection. Continu­ous flow injection analyses (FIA) are well known to present numerous advantages over batch methods. Furthermore, the development of on-chip micro-channel analytical (μFIA) systems begun and have gained much attention within the last two decades in view of the striking advantages over conventional FIA techniques. This paper reviews published information on detection of phosphomolybdenum blue in conventional systems as well as on micro-chip. It reports on the challenges encountered (interference from other complex anions), the achieve­ments made so far (intereference removal by electrokinetic separation) and what the future holds (simultaneous determination).

Detection of ergosterol using liquid chromatography/electrospray ionization mass spectrometry: Investigation of unusual in-source reactions.

In the field of natural products, de-replication of complex mixtures has become a usual practice to annotate known compounds and avoid their re-isolation. For this purpose, many groups rely on liquid chromatography coupled to high-resolution mass spectrometry (HPLC/MS) to deduce molecular formulae of compounds allowing comparison with public or in-house databases. Electrospray ionization (ESI) is usually considered as the method of choice for investigating a large panel of compounds but, in some cases, it may lead to unusual results as described in this article for ergosterol. Ergosterol and other fungal sterols in methanolic solution were analysed using various chromatographic gradients with HPLC/MS using both ion trap time-of-flight MS and Orbitrap MS instruments fitted with an ESI source. Further flow injection analyses were performed to investigate the influence of the solvent composition. MS/MS fragmentation data were acquired to annotate the various ions observed. Contrary to other fungal sterols, ergosterol was found to be highly sensitive to oxidation during ESI. Putative structures were proposed based on MS/MS studies and known oxidation mechanisms of ergosterol by reactive oxygen species that could be formed in the ESI process. The proportion of acetonitrile in the eluent was found to influence this in-source oxidation, with an increased proportion of oxidized sodium adducts with higher proportions of acetonitrile. While ergosterol is a major sterol found in fungi, this study investigates its ionization by electrospray for the first time. The results reported here will help further detection and annotation of this compound in fungal extracts after HPLC/ESI-MS analyses.

Modified Screen Printed Electrode Suitable for Electrochemical Measurements in Gas Phase.

We describe a convenient assembly for screen printed carbon electrodes (SPCE) suitable for analyses in gaseous samples which are of course lacking in supporting electrolytes. It consists of a circular crown of filter paper, soaked in a RTIL or a DES, placed upon a disposable screen printed carbon cell, so as to contact the outer edge of the carbon disk working electrode, as well as peripheral counter and reference electrodes. The electrical contact between the paper crown soaked in RTIL or DES and SPCE electrodes is assured by a gasket, and all components are installed in a polylactic acid holder. As a result of this configuration, a sensitive, fast-responding, membrane-free gas sensor is achieved where the real working electrode surface is the boundary zone of the carbon working disk contacted by the paper crown soaked in the polyelectrolyte. This assembly provides a portable and disposable electrochemical platform, assembled by the easy immobilization onto a porous and inexpensive supporting material such as paper of RTILs or DESs which are characterized by profitable electrical conductivity and negligible vapor pressure. The electroanalytical performance of this device was evaluated by voltammetric and flow injection analyses of oxygen which was chosen as prototype of electroactive gaseous analytes. The results obtained pointed out that this assembly is very profitable for the analysis of gaseous atmospheres, especially when used as detector for FIA in gaseous streams.

Milk β-hydroxybutyrate concentration measured by Fourier-transform infrared and flow-injection analyses from samples taken at different times relative to milking.

Analysis of milk BHB concentration by Fourier-transform infrared (FTIR) spectrometry more frequently than regular milk testing could help dairy producers in decision making, particularly if it would be possible to use small hand-stripped samples (hereinafter simply called samples) taken between dairy herd improvement (DHI) test-samples analysed using DHI algorithms. The aim of this Research Communication was to evaluate milk BHB concentration and the prevalence of elevated milk BHB concentration analysed by FTIR spectrometry compared with flow-injection analysis (SKALAR) from samples taken at different times relative to the milking. A total of 293 early-lactation cows in 44 commercial dairy herds were involved in the study. Herds were visited once during the morning milking when a routine DHI test-sample was obtained using in-line milk samplers. Additional milk samples were taken by hand stripping as follows: (1) Just before connecting the milking machine; (2) immediately after removing the milking machine; (3) 3 h after milking and (4) 6 h after milking. Milk samples were analysed for BHB concentration by FTIR and SKALAR, the latter being the reference method. Milk BHB concentration from samples taken before milking was different between FTIR and SKALAR whereas no difference was noted for other sampling times, although milk BHB concentration rose as time after milking increased. Except for DHI test-samples for which prevalence was not different between analysis methods, prevalence of elevated milk BHB concentration (≥0.15 mmol/l) was greater for FTIR analysis. However, no difference in prevalence was observed between SKALAR and FTIR when using a threshold of ≥0.20 mmol/l. In summary, hand-stripped milk samples taken any time after removing the milking machine until 6 h after the milking can be recommended for FTIR analysis of elevated milk BHB concentration prevalence provided a threshold of 0.20 mmol/l is used.

Chemiluminescence quenching microarrays for high throughput screening of antioxidants and its application in evaluating herbal extracts and pure compounds

In this paper, a novel high throughput screening method for antioxidants was described. The screening process was completed on a 5 cm × 5 cm silica gel 60 plate. Luminol was used as the fluorogenic substrate while hydrogen peroxide employed to excite the chemiluminescence. A dark spot was observed due to quenching effect of antioxidant. A linear model of the integral area of the spot as a function of analyte amount was fit by using vitamin C as positive control. Excellent linearity (R2 = 0.9978) was obtained in the range of 2.31–23.1 μg. The variation coefficients of intra- and inter-chip precisions were below 5% (n = 10) and 10% (n = 6) respectively. The new method was validated by comparing the analysis result of six flavonoids with that from a sequential injection method. The Pearson correlation coefficient was up to 0.98. A set of traditionally used herbal medicines was screened, and Rhei Radix et Rhizoma showed the strongest signal. The major bioactive ingredients were further assigned by flow injection and MS analyses. These results reveal the prospects of the proposed method to supply a promising tool in vitro for high throughput screening and activity evaluation of antioxidants in a fast, low-cost and reliable manner.

In-situ preparation of Au(111) oriented nanoparticles trapped carbon nanofiber-chitosan modified electrode for enhanced bifunctional electrocatalysis and sensing of formaldehyde and hydrogen peroxide in neutral pH solution

A unique gold(111) oriented nanoparticles trapped carbon nanofiber-chitosan modified electrocatalyst coated glassy carbon electrode(GCE/CNF-CHIT@Aunano) was prepared by an in-situ electrochemical procedure for efficient bifunctional electrocatalytic oxidation and reduction of formaldehyde and hydrogen peroxide in neutral pH solution. In the typical preparation, a microliter quantity of Au3+ solution was drop-casted on GCE/CNF-CHIT surface and potential cycled in pH 7 PBS. The GCE/CNF-CHIT@Aunano showed well-defined electrochemical response of gold nanoparticles of calculated electrochemically active surface area, 0.1347cm2, which is about 3–3000 times higher than that of the surface area of the respective unmodified electrodes such as polycrystalline Au (0.0407cm2), GCE/CNF@Aunano (0.0034cm2) and GCE@Aunano (0.0005cm2). Physicochemical characterizations such as FESEM, EDAX, TEM, XRD, Raman, FTIR and XPS spectroscopic techniques revealed stabilization of 10±5nm sized Au(111) phase oriented nanoparticles by the amino functional group of chitosan in the composite matrix. The detailed electrochemical characterization by cyclic voltammetry(CV), rotating disk electrode (RDE) and in-situ CV-electrochemical quartz crystal microbalance (EQCM; Mw=44±1gmol−1 species was identified) techniques showed direct oxidation of formaldehyde to formate as an intermediate (45gmol−1) without any CO poisoning, unlike the conventional Pt and Au based electrodes. Using a bipotentiostat, selective and simultaneous flow injection analyses of formaldehyde and hydrogen peroxide in a mixture at discreet applied potentials (Eapp=0.5V/0.15V and −0.15V vs Ag/AgCl) were demonstrated. The applicability of the GCE/CNF-CHIT@Aunano was tested by detecting formaldehyde and hydrogen peroxide in a commercial hair dye formulation with about 100% recovery values.

Nanostructured Alpha-NiCe Mixed Hydroxide for Highly Sensitive Amperometric Prednisone Sensors

Nickel hydroxide nanoparticles with enhanced electrocatalytic activity and stability in the alpha phase were prepared by incorporation of 20 atom% of Ce(III) ions, that were shown to be oxidized to the catalytic active Ce(IV) species in the mixed hydroxide/oxide nanomaterial. Alpha-NiCe is constituted by smaller nanoparticles as compared with pure nickel hydroxide and can interact with prednisone, a widely prescribed medicine that is controlled by the International Anti-Doping Agency because of its use as anabolic agent. This compound is more or less easily hydroxilated by oxygen and then oxidized to the respective keto species, that was shown to be oxidized further by the modified electrodes upon loss of the alkyl side chain. Thus, a sensitive prednisone sensor was demonstrated exploring the electrocatalytic oxidation reaction instead of the reduction of prednisone to prednisolone, as previously reported in the literature. Sensitivity as high as 3.9×10−2Amol−1L/cm2 and limit of detection as low as 8.4×10−9molL−1 were achieved using flow injection analyses.

Electrochemical determination of cephalosporins using a bare boron-doped diamond electrode

The electrochemical oxidation of seven cephalosporins (ceftriaxone, cefotaxime, ceftazidime, cefadroxil, cefuroxime, cefaclor, cefalexin) was evaluated at high potential, using a bare boron-doped diamond electrode and the influence on the analytical response of the side chains was investigated. Based on the anodic oxidation of the cephalosporin nucleus, a simple and sensitive method was developed for the electrochemical detection of cefalexin by differential pulse voltammetry. After the optimization of the experimental conditions, a linear correlation was obtained between the peak height and the molar concentration of cefalexin in the range of 0.5 μM–700 μM, with a limit of detection of 34.74 ng mL−1. The anodic peak for cefalexin was evaluated in the presence of other cephalosporin molecules and of other common interferents. The developed method was applied to detection of cefalexin from real environmental, biomedical and pharmaceutical samples, with good results. The electrochemical oxidation of cephalosporins was successfully adapted for flow injection analyses, with sensitive and reproducible successive analyses of cefalexin, in different concentrations. The flow analyses allowed also the determination of the total amount of cephalosporins found in the sample.

Open Access UHPSFC/MS - an additional analytical resource for an academic mass spectrometry facility.

Many compounds submitted for analysis in Chemistry at the University of Southampton do not retain, elute or ionize using open access reversed-phase ultra-high-performance liquid chromatography/mass spectrometry (RP-UHPLC/MS) and require analysis via infusion. An ultra-high-performance supercritical fluid chromatography mass spectrometry approach was implemented to afford high-throughput analysis of these compounds with chromatographic separation. A UPC(2) -TQD MS system has been incorporated into the open access MS provision within Chemistry at the University of Southampton, using an ESCi source (electrospray and atmospheric pressure chemical ionization) and an atmospheric pressure photoionization (APPI) source. Access to instrumentation is enabled via a web-based interface (RemoteAnalyzer™). Compounds such as fluorosugars, fullerenes, phosphoramidites, porphyrins, and rotaxanes exhibiting properties incompatible with RP-UHPLC/MS have been analyzed using automated chromatography and mass spectrometry methods. The speedy return of data enables research in these areas to progress unhindered by sample type. The provision of an electronic web format enables easy incorporation of chromatograms and mass spectra into electronic files and reports. The implementation of UHPSFC/MS increases access to a wide range of chemistries incompatible with reversed-phase chromatography and polar solvents, enabling more than 90% of submitted samples to be analyzed using an open access approach. Further, chromatographic separation is provided where previously flow injection or infusion analyses were the only options. Copyright © 2016 John Wiley & Sons, Ltd.

Plasma-Assisted Reaction Chemical Ionization for Elemental Mass Spectrometry of Organohalogens

We present plasma-assisted reaction chemical ionization (PARCI) for elemental analysis of halogens in organic compounds. Organohalogens are broken down to simple halogen-containing molecules (e.g., HBr) in a helium microwave-induced plasma followed by negative mode chemical ionization (CI) in the afterglow region. The reagent ions for CI originate from penning ionization of gases (e.g., N2) introduced into the afterglow region. The performance of PARCI-mass spectrometry (MS) is evaluated using flow injection analyses of organobromines, demonstrating 5-8 times better sensitivities compared with inductively coupled plasma MS. We show that compound-dependent sensitivities in PARCI-MS mainly arise from sample introduction biases.