Analytica Chimica Acta (v.713, #C)

Display Omitted► A long-wavelength fluorimetric method for the determination of polyphenols is reported. ► The method involves the use of laccase, indocyanine green and gold nanoparticles. ► The delay caused by polyphenols on the enzymatic oxidation of the fluorophor is used for analytical purposes. ► The interaction of gold nanoparticles and laccase allows the improvement of the detection limits obtained. ► The method has been satisfactorily applied to the analysis of beverages.An enzymatic fluorimetric method for the determination of polyphenol compounds in beverages is described, which is based on the temporal inhibition caused by these compounds on the oxidation of the long wavelength fluorophor indocyanine green (λ ex 764 nm, λ em 806 nm), in the presence of the enzyme laccase and positively charged gold nanoparticles (AuNPs). The oxidation of the dye gives rise to a fast decrease in its fluorescence, but it is delayed by the polyphenol, obtaining a time period directly proportional to its concentration, which has been used as the analytical parameter. The behaviour of several benzenediols and benzenetriols in the system and the modification of the activity of the enzyme by its interaction with AuNPs have been studied.The system has been optimized using gallic acid as a polyphenol model, but the dynamic ranges of the calibration graphs and the detection limits for several of the polyphenols assayed were obtained (μmol L−1): gallic acid (0.13–5, 0.04), catechol (0.08–5, 0.01), hydroquinone (0.05–2, 0.01), hydroxyhydroquinone (0.09–5, 0.03), pyrogallol (0.17–5, 0.04). Most of the values of the regression coefficients were 0.999 and the precision of the method, expressed as RSD% and checked at two concentration levels of each analyte, ranged between 1.8 and 5.6%. The method has been applied to the determination of polyphenol content in several foodstuff samples and the results compared with those obtained with the standard Folin–Ciocalteu method.
Keywords: Polyphenols; Laccase; Gold nanoparticles; Stopped-flow mixing technique; Long wavelength fluorimetric detection; Beverage samples;

High resolution separation methods for the determination of intact human erythropoiesis stimulating agents. A review by Michel Girard; Angel Puerta; Jose Carlos Diez-Masa; Mercedes de Frutos (7-22).
.Display Omitted► Methods to analyze EPO and other erythropoiesis stimulating agents (ESAs) are needed. ► Characterization of biopharmaceuticals and doping control are required. ► HPLC and CE enable to perform analysis of EPO and other ESAs. ► These techniques allow separating glycoprotein isoforms, aggregates or excipients. ► Sample preparation and detection methods could help to overcome present limitations.Human erythropoietin (hEPO), a hormone involved in the formation of red blood cells, is a 30 kDa glycoprotein with a high carbohydrate content. The production of recombinant hEPO has made possible its widespread therapeutic use and its banned use in competition sports. Methods to analyze EPO and other erythropoiesis stimulating agents (ESAs) are necessary for the characterization and quality control of these biopharmaceuticals and also for doping control. In this paper, high resolution separation methods, namely high performance liquid chromatography (HPLC) and capillary electrophoresis (CE), with special attention to CE-coupled mass spectrometry, are reviewed. The usefulness of these techniques when applied in different modes to separate the glycoprotein isoforms, aggregates or excipients are detailed. In addition, sample preparation methods that have been applied to ESA samples for subsequent determination by HPLC or CE, as well as the potential compatibility of other preparation methods, are discussed. Applications of the HPLC and CE methods regarding regulatory considerations for biopharmaceuticals analysis, with emphasis on biosimilars, and doping control are also included. Finally, limitations of the present methods and their possible solutions are considered.
Keywords: Erythropoietin (EPO); Capillary electrophoresis; High performance liquid chromatography; Mass spectrometry; Doping control; EPO biosimilars;

Development of salt-tolerance interface for an high performance liquid chromatography/inductively coupled plasma mass spectrometry system and its application to accurate quantification of DNA samples by Yuka Takasaki; Shinnosuke Sakagawa; Kazumi Inagaki; Shin-Ichiro Fujii; Akhmad Sabarudin; Tomonari Umemura; Hiroki Haraguchi (23-29).
Display Omitted► The capillary-attached micronebulizer allowed total consumption of DNA samples. ► The micronebulizer was applied as an interface for hyphenation of HPLC with ICP-MS. ► 20 bp DNA ladder fragments and oligonucleotides were quantitatively determined.Accurate quantification of DNA is highly important in various fields. Determination of phosphorus by ICP-MS is one of the most effective methods for accurate quantification of DNA due to the fixed stoichiometry of phosphate to this molecule. In this paper, a smart and reliable method for accurate quantification of DNA fragments and oligodeoxythymidilic acids by hyphenated HPLC/ICP-MS equipped with a highly efficient interface device is presented. The interface was constructed of a home-made capillary-attached micronebulizer and temperature-controllable cyclonic spray chamber (IsoMist). As a separation column for DNA samples, home-made methacrylate-based weak anion-exchange monolith was employed. Some parameters, which include composition of mobile phase, gradient program, inner and outer diameters of capillary, temperature of spray chamber etc., were optimized to find the best performance for separation and accurate quantification of DNA samples. The proposed system could achieve many advantages, such as total consumption for small amount sample analysis, salt-tolerance for hyphenated analysis, high accuracy and precision for quantitative analysis. Using this proposed system, the samples of 20 bp DNA ladder (20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 300, 400, 500 base pairs) and oligodeoxythymidilic acids (dT12–18) were rapidly separated and accurately quantified.
Keywords: Quantification of DNA; Micronebulizer; Monolithic column; Phosphorus; Hyphenated technique;

Display Omitted► Extract much more information contents hidden in the chromatograms. ► Use a best-first search strategy to determine the optimal features combination. ► The present QPER model performs better than the traditional ones. ► The present QPER model is very helpful for re-developing the herbal drugs.Herbal medicine has been successfully applied in clinical therapeutics throughout the world. In this paper, various information contents in addition to a best-first search strategy are proposed for improving prediction quality of quantitative profile–efficacy relationship (QPER). As a demonstration, a QPER model was constructed to predict the blood-clotting time increasing effect of Naodesheng prescription, a widely used herbal medicine in China. Evaluated by both the self-consistency test and the rigorous jackknife test, the predictive accuracy was increased by feeding the model with the merged information contents compared to only with the common chromatographic peak areas. The confirmation experiment exhibited that the predicted blood-clotting time were well consistent with the observed values. Furthermore, it has not escaped from our notice that the important potential application of the current QPER model is to be extended to help search active fractions, which has attracted more and more attention in the re-developments of herbal medicines based on the active compounds.
Keywords: Information theory; Best-first search; Quantitative profile–efficacy effect; Herbal medicine; Active fraction;

Display Omitted► The computational approach was used for investigation of MIP for cyanazine. ► Precipitation polymerization was used for synthesis of cyanazine-MIP mediator. ► The MIPs were used as selective mediator in construction of modified CP electrode. ► This sensor has been applied for the determination of cyanazine in food samples.A computational approach was used for screening functional monomers and polymerization solvent in the rational design of molecularly imprinted polymers (MIPs). It was based on the comparison of the binding energy of the complexes between the template and functional monomers. On the basis of computational results, acrylamide (AAM) and toluene were selected as functional monomer and polymerization solvent, respectively. The MIP, embedded in the carbon paste electrode, functioned as a selective recognition element and pre-concentrator agent for cyanazine determination by using cathodic stripping voltammetric method. The MIP-CP electrode showed very high recognition ability in comparison with NIP-CPE. Some parameters affecting the sensor response were optimized, and then the calibration curve was plotted. A dynamic linear range of 5.0–1000 nM was obtained. The detection limit of the sensor was calculated as 3.2 nM. This sensor was successfully used for cyanazine determination in food samples.
Keywords: Cyanazine; Molecularly imprinted polymer; Cathodic stripping voltammetry; Carbon paste; Computational approach;

Display Omitted► Bst DNA polymerase shows specific function on the T–Hg2+–T biomimetic structure. ► T–Hg2+–T can be formed in the presence of Hg2+, thus induces the RCA reaction. ► Sub-nanomolar sensitivity and excellent selectivity were achieved for Hg2+ detection.In this study, we firstly demonstrated that Bst DNA polymerase shows specific recognition and function on the T–Hg2+–T biomimetic structure. Based on this, a novel available electrochemiluminescence (ECL) sensor for Hg2+ has been developed. In this strategy, magnet beads tagged primer was designed to complementary to the region of the circular padlock probe but with two T–T mismatches at the 3′ end. The mismatched primers cannot be extended by Bst DNA polymerase in the absence of Hg2+. Stable T–Hg2+–T can be formed in the presence of Hg2+, thus induces the elongation and amplification reaction by DNA polymerase with a rolling circular amplification (RCA) mechanism. Subsequently, the resulted RCA products are hybridized with the tris (bipyridine) ruthenium (TBR)-tagged probes and detected by ECL platform. Current method shows a sub-nanomolar sensitivity and excellent selectivity over a spectrum of interference metal ions.
Keywords: Eectrochemiluminescence; Rolling circular amplification; Biomimetic structure; Hg2+ detection;

Electrochemical immunoassay of cotinine in serum based on nanoparticle probe and immunochromatographic strip by Hungchi Nian; Jun Wang; Hong Wu; Jiunn-Guang Lo; Kong-Hwa Chiu; Joel G. Pounds; Yuehe Lin (50-55).
Display Omitted► Using nanoparticle probe in immunochromatographic strip. ► Enhanced sensitivity by using nanoparticle label. ► Rapid and sensitive detection of cotinine in serum.A disposable sensor for the determination of cotinine in human serum was developed based on immunochromatographic test strip and quantum dot label. In this assay, cotinine linked with quantum dot competes with cotinine in sample to bind to anti-cotinine antibody in the test strip and the quantum dots serve as signal vehicles for electrochemical readout. Some parameters governing the performance of the sensor were optimized. The sensor shows a wide linear range from 1 ng mL−1 to 100 ng mL−1 cotinine with a detection limit of 1.0 ng mL−1. The sensor was validated with spiked human serum samples and it was found that this method was reliable in measuring cotinine in human serum. The results demonstrate that this sensor is rapid, accurate, and less expensive and has the potential for point of care (POC) detection of cotinine and fast screening of tobacco smoke exposure.
Keywords: Immunochromatographic strip; Quantum dots; Biomarker; Cotinine; Nanotechnology;

Display Omitted► Synergy of ultrasound energy and TILDLME technique for improved metal extraction. ► Highly selective determination of inorganic Co species at trace levels. ► Speciation analysis of Co in several nutritional supplements with highly complex matrices. ► Development of an environmentally friendly microextraction technique with minimal waste production and sample consumption.In the present work, a simple and rapid analytical method based on application of ionic liquids (ILs) for inorganic Co(II) species (iCo) microextraction in a variety of nutrient supplements was developed. Inorganic Co was initially chelated with 1-nitroso-2-naphtol (1N2N) reagent followed by a modern technique named ultrasound-assisted temperature-controlled ionic liquid dispersive liquid phase microextraction (USA-TILDLME). The extraction was performed with 1-hexyl-3-methylimidazolium hexafluorophosphate [C6mim][PF6] with the aid of ultrasound to improve iCo recovery. Finally, the iCo-enriched IL phase was solubilized in methanol and directly injected into an electrothermal atomic absorption spectrometer (ETAAS). Several parameters that could influence iCo microextraction and detection were carefully studied. Since the main difficulty in these samples is caused by high concentrations of potential interfering ions, different approaches were evaluated to eliminate interferences. The limit of detection (LOD) was 5.4 ng L−1, while the relative standard deviation (RSD) was 4.7% (at 0.5 μg L−1 Co level and n  = 10), calculated from the peak height of absorbance signals. Selective microextraction of iCo species was achieved only by controlling the pH value during the procedure. The method was thus successfully applied for determination of iCo species in nutritional supplements.
Keywords: 1-Hexyl-3-methylimidazolium hexafluorophosphate; Ionic liquid; Microextraction; Cobalt; Nutritional supplements;

Display Omitted► Polyaniline–polyamide nanofiber mat was fabricated by electrospinning technology. ► Electrospun nanofiber was used for extraction of chlorobenzenes from aquatic media. ► A method based on headspace adsorptive microextraction and GC–MS was developed.A headspace adsorptive microextraction technique was developed using a novel polyaniline-nylon-6 (PANI-N6) nanofiber sheet, fabricated by electrospinning. The homogeneity and the porosity of the prepared PANI-N6 sheet were studied using the scanning electron microscopy (SEM) and nanofibers diameters were found to be around 200 nm. The novel nanofiber sheet was examined as an extracting medium to isolate some selected chlorobenzenes (CBs), as model compounds, from aquatic media. The extracted analytes were desorbed using μL-amounts of solvent and eventually an aliquot of extractant was injected into gas chromatography–mass spectrometry (GC–MS). Various parameters affecting the extraction and desorption processes were optimized. The developed method proved to be convenient and offers sufficient sensitivity and a good reproducibility. Limits of detection achieved for CBs with the developed analytical procedure ranged from 19 to 33 ng L−1, while limits of quantification were from 50 to 60 ng L−1. The relative standard deviations (RSD) at a concentration level of 0.1 ng mL−1 and 1 ng mL−1 were in the range of 8–14% and 5–11% (n  = 3), respectively. The calibration curves of analytes were investigated in the range of 50–1000 ng L−1 and R 2 between 0.9739 and 0.9932 were obtained. The developed method was successfully applied to the extraction of selected CBs from tap and river water samples. The relative recovery (RR) percentage obtained for the spiked real water samples at 0.1 ng mL−1 and 1 ng mL−1 level were 93–103% and 95–104%, respectively. The whole procedure showed to be conveniently applicable and quite easy to handle.
Keywords: Polyaniline-nylon-6 nanofibers; Electrospinning; Headspace adsorptive microextraction; Gas chromatography–mass spectrometry; Chlorobenzenes;

Display Omitted► A simple dispersive liquid–liquid microextraction (DLLME) method has been developed for the first time. ► Enrichment factors of the proposed method were higher than those of conventional DLLME. ► The new method avoided using high density and toxic extraction solvents. ► Short extraction time of the present method relative to the other methods was another advantage of this method.In the present work a new, simple, rapid and environmentally friendly dispersive liquid–liquid microextraction (DLLME) method has been developed for extraction/preconcentration of some triazole pesticides in aqueous samples and in grape juice. The extract was analyzed with gas chromatography–flame ionization detection (GC–FID) or gas chromatography–mass spectrometry (GC–MS). The DLLME method was performed in a narrow-bore tube containing aqueous sample. Acetonitrile and a mixture of n-hexanol and n-hexane (75:25, v/v) were used as disperser and extraction solvents, respectively. The effect of several factors that influence performance of the method, including the chemical nature and volume of the disperser and extraction solvents, number of extraction, pH and salt addition, were investigated and optimized. Figures of merit such as linearity (r 2  > 0.995), enrichment factors (EFs) (263–380), limits of detection (0.3–5 μg L−1) and quantification (0.9–16.7 μg L−1), and relative standard deviations (3.2–5%) of the proposed method were satisfactory for determination of the model analytes. The method was successfully applied for determination of target pesticides in grape juice and good recoveries (74–99%) were achieved for spiked samples. As compared with the conventional DLLME, the proposed DLLME method showed higher EFs and less environmental hazards with no need for centrifuging.
Keywords: Dispersive liquid–liquid microextraction; Gas chromatography; Grape juice; Narrow-bore tube; Triazole pesticides;

Display Omitted► A method based on hollow fiber liquid phase microextraction (HF-LPME) was developed. ► HF-LPME was applied for the first time to aerosols for pinic and pinonic acid analysis. ► Very low limits of detections under 50 pg m−3 were obtained. ► An enrichment factor up-to 28,050 times was obtained that is higher than already published results.A method based on hollow fiber liquid phase microextraction (HF-LPME) for analysis of pinic acid and pinonic acid was developed and for the first time successfully applied to ambient aerosol samples. In this method, the aerosol samples were dissolved in 0.05 M H2SO4 and the solution was extracted using three-phase HF-LPME where donor phase was 0.1 M (NH4)2CO3. Different parameters like type of organic solvent for membrane phase, extraction time and stirring speed etc. were optimized. Optimum extraction time was 4.5 h and optimum-stirring speed was found to be 900 rpm. We used 6-undecanone as organic phase along with tri-n-octylphosphine oxide (optimum TOPO contents was 15% w/v), which gave an enormous enrichment for both pinic and pinonic acid. Enrichment factors of 28,050 and 27,400 times were obtained for pinonic acid and pinic acid, respectively, that are the highest ever published. The extraction efficiency for pinic acid and pinonic acid were 68.5% and 70.1%, respectively. Very low limits of detection were obtained. Values of 1.0 ng L−1 and 0.5 ng L−1 in aqueous solutions, corresponding to 24 pg m−3 and 12 pg m−3 in aerosol samples were the limits of detections for pinonic acid and pinic acid, respectively. Both pinonic acid and pinic acid were found in all aerosol samples analyzed.
Keywords: Aerosols; Hollow fiber liquid phase microextraction; Pinene photo-oxidation; Pinic acid; Pinonic acid;

Display Omitted► Formation of radical sulfate during the fusion process. ► Acquiring better results than mix acid including hydrofluoric acid. ► Faster process than microwave and hot plate methods of digestion. ► Applicable to both inorganic and organic samples.Titanium dioxide (i.e. TiO2) in nano-form is a constituent of many nanomaterials that are used in sunscreens, cosmetics, industrial products and in biomedical applications. Quantification of TiO2 nanoparticles in various matrixes is a topic of great interest for researchers studying the potential health and environmental impacts of nanoparticles. However, analysis of TiO2 as Ti4+ is difficult because current digestion techniques require use of strong acids that may be a health and safety risk in the laboratory. To overcome this problem, we developed a new method to digest TiO2 nanoparticles using ammonium persulfate as a fusing reagent. The digestion technique requires short times to completion and optimally requires only 1 g of fusing reagent. The fusion method showed >95% recovery of Ti4+ from 6 μg mL−1 aqueous suspensions prepared from 10 μg mL−1 suspension of different forms of TiO2, including anatase, rutile and mixed nanosized crystals, and amorphous particles. These recoveries were greater than open hot-plate digestion with a tri-acid solution and comparable to microwave digestion with a tri-acid solution. Cations and anions commonly found in natural waters showed no significant interferences when added to samples in amounts of 10 ng to 110 mg, which is a much broader range of these ions than expected in environmental samples. Using ICP-MS for analysis, the method detection limit (MDL) was determined to be 0.06 ng mL−1, and the limit of quantification (LOQ) was 0.20 ng mL−1. Analysis of samples of untreated and treated wastewater and biosolids collected from wastewater treatment plants yielded concentrations of TiO2 of 1.8 and 1.6 ng mL−1 for the wastewater samples, respectively, and 317.4 ng mg−1 dry weights for the biosolids. The reactions between persulfate ions and TiO2 were evaluated using stoichiometric methods and FTIR and XRD analysis. A formula for the fusing reaction is proposed that involves the formation of sulfate radicals.
Keywords: Nanoparticles; Titanium dioxide; Digestion; Fusion; Ammonium persulfate; ICP-MS;

An approach to performing extraction and preconcentration employing functionalized magnetic particles for the determination of cobalt in the sequential injection lab-on-valve system using detection by electrothermal atomic absorption spectrometry.Display Omitted► New SPE method for cobalt separation/preconcentration was reported. ► Functionalized magnetic nanoparticles were used as adsorbent. ► Extraction, elution, and detection procedures were performed in the LOV system. ► This automatic extraction technique provided a good platform for metal analysis.A new approach to performing extraction and preconcentration employing functionalized magnetic nanoparticles for the determination of trace metals is presented. Alumina-coated iron oxide nanoparticles were synthesized and used as the solid support. The nanoparticles were functionalized with sodium dodecyl sulfate and used as adsorbents for solid phase extraction of the analyte. Extraction, elution, and detection procedures were performed sequentially in the sequential injection lab-on-valve (SI-LOV) system followed by electrothermal atomic absorption spectrometry (ETAAS). Mixtures of hydrophobic analytes were successfully extracted from solution using the synthesized magnetic adsorbents. The potential use of the established scheme was demonstrated by taking cobalt as a model analyte. Under the optimal conditions, the calibration curve showed an excellent linearity in the concentration range of 0.01–5 μg L−1, and the relative standard deviation was 2.8% at the 0.5 μg L−1 level (n  = 11). The limit of detection was 6 ng L−1 with a sampling frequency of 18 h−1. The present method has been successfully applied to cobalt determination in water samples and two certified reference materials.
Keywords: Sequential injection lab-on-valve; Electrothermal atomic absorption spectrometry; Magnetic nanoparticles; Cobalt;

Display Omitted► We used ICP-MS with microwave digestion for determination of REE in different rocks. ► Syenites, granodiorites and albitized granites are not digested in the MW at 210 °C. ► We explain this fact by the presence of stable saturated silicate–albite NaAlSi3O8. ► These rocks can be digested completely only by fusion with lithium metaborate.Different methods of rock sample digestion for final analysis by ICP-MS technique are investigated. It is shown that only basic rocks can be quantitatively digested in a microwave (MW) field with the mixture of HF and HNO3 acids at 210 °C for 60 min. The addition of HCl and H3BO3 provides complete digestion of andesites and some types of granites. Even at maximal temperature in the used MW oven of 210 °C syenites, granodiorites and albitized granites are not digested. These types of rocks are not digested in a closed Teflon autoclave for 16 h and can be digested only by fusion with lithium metaborate. The reason for such behavior is discussed. To avoid problems with the introduction of heavily acidic solutions after fusion in ICP the solutions were diluted. To compensate the loss of sensitivity due to the dilution step the REEs (Rare Earth Elements) pre-concentration using aminocarboxylic Pol-DETATA (diethyltriaminetetraacetate) sorbent was tested. The developed scheme is validated by the analysis of a wide range of reference rock materials.
Keywords: Rock samples; Microwave digestion; Fusion; Inductively coupled plasma mass spectrometry;

Direct affinity screening chromatography–mass spectrometry assay for identification of antibacterial agents from natural product sources by Kevin A. Schug; Evelyn Wang; Sijia Shen; Sunaina Rao; Stephanie M. Smith; Laura Hunt; Laura D. Mydlarz (103-110).
Display Omitted► Novel affinity mass spectrometry assay for natural product drug discovery. ► Assay based on monitoring complex formation with a target ligand mimic. ► Lysine–d-alanine–d-alanine used as Gram positive target ligand. ► Potential antibacterial compound tracked through fractionation of coral extract.A direct affinity screening – mass spectrometry assay, coupled to liquid chromatography, is presented as a tool for natural product drug discovery. Using the assay, fractionated extracts from a Caribbean gorgonian coral were shown to contain a new chemical entity (NCE) which binds to a mimic of the Gram positive bacterial cell wall (lysine–d-alanine–d-alanine). Conditions for observation of a specific noncovalent complex between the NCE and the target mimic using electrospray ionization-mass spectrometry were validated in a series of positive and negative control experiments, which featured flow injection analysis-based titrations. While the structural identity of the NCE could not be determined due to limited sample quantities, this work provides proof-of-principle for such an approach to potentially accelerate drug discovery from natural product sources.
Keywords: Natural products; Noncovalent interactions; Electrospray ionization; Dynamic titration; Pseudoplexaura porosa;

NaYF4:Yb3+/Er3+ upconversion nanocrystals with a mean size of about 50 nm were synthesized by hydrothermal method. Based on NaYF4:Yb3+/Er3+ as donor and 4-((4-(2-aminoethylamino)naphthalen-1-yl)diazenyl) benzenesulfonic acid dihydrochloride (production of Griess Reaction, which was in proportion to the trace amounts of nitrite) as acceptor, an efficient fluorescence energy transfer system was developed for selective and sensitive determination of trace nitrite.Display Omitted► Stable NaYF4:Yb3+, Er3+ upconversion luminescence nanocrystals were prepared. ► NaYF4:Yb3+, Er3+ upconversion nanocrystals were used as donor. ► An efficient upconversion luminescence energy transfer (LET) system was developed. ► The system was developed for selective and sensitive determination of trace nitrite.Based on NaYF4:Yb3+, Er3+ upconversion nanocrystals as donor and 4-((4-(2-aminoethylamino)naphthalen-1-yl)diazenyl) benzenesulfonic acid dihydrochloride (ANDBS) as acceptor, an efficient luminescence energy transfer (LET) system was developed for selective and sensitive determination of trace amounts of nitrite. Based on Griess Reaction, ANDBS was generated by the quantitative reaction of nitrite, sulfanilamide and N-(1-naphtyl)-ethylenediamine dihydrochloride (N1NED). The degree of the overlaps between the emission spectrum of NaYF4:Yb3+, Er3+ and the absorption spectrum of ANDBS were effective for luminescence energy transfer. Under the optimal condition, the upconversion luminescence quenching of NaYF4:Yb3+, Er3+ was in proportion to the trace amounts of nitrite. The detection limit for nitrite achieved is 0.0046 μg mL−1 and the system shows high sensitivity towards nitrite at 0.008000–0.2500 μg mL−1 range.
Keywords: Upconversion luminescence nanocrystal; Luminescence energy transfer; Griess Reaction; Nitrite; Determination;

Simultaneous impedimetric and amperometric interrogation of renal cells exposed to a calculus-forming salt by Szilveszter Gáspár; Sorin David; Cristina Polonschii; Irene Marcu; Mihaela Gheorghiu; Eugen Gheorghiu (115-120).
Display Omitted► A system allowing the simultaneous and real-time monitoring of both cell adherence and superoxide release into the extracellular space was developed. ► The system was used to observe how these two cellular parameters are changing in real-time for renal cells exposed to calcium oxalate. ► Calcium oxalate crystals decrease cell adherence and in the same time induce oxidative stress by an overproduction of superoxide.The complexity of the cellular response, induced even by the simplest experimental stimulus, requires an increased number of cellular parameters to be simultaneously monitored. An all electrochemical system allowing the simultaneous and real-time monitoring of both cell adherence and superoxide release into the extracellular space was developed to address this challenge. Cell adherence (to neighboring cells and to substrate) was monitored using non-faradaic impedance spectroscopy while the superoxide release was monitored using a cytochrome c-based amperometric biosensor. The system was used to observe for the first time how these two cellular parameters are changing in real-time for renal cells exposed to calcium oxalate, a calculus-forming salt. It was discovered that calcium oxalate crystals decrease cell adherence and in the same time induce oxidative stress by an overproduction of superoxide. Subconfluent cells, without fully developed tight junctions, appear to be more vulnerable than confluent cells with tight junctions indicating the important protective role of these junctions.
Keywords: Superoxide biosensor; Impedance spectroscopy; Amperometric detection; Renal cells; Oxidative stress; Cellular adherence;

Display Omitted► Many lignans in Schisandra chinensis were separated by the 2D-HPLC–DAD–MS. ► The ILC column can mimic the biological membranes. ► More than 40 components were resolved and 14 compounds were identified. ► The 3D chromatographic fingerprints were preliminarily established. ► PCA and HCA were preliminarily used to processes the 3D fingerprints.A comprehensive two-dimensional (2D) separation is one that employs two separation dimensions (columns) and draws on all of the available resolving power from each of the dimensions of separate the components in a sample. In this study, a comprehensive 2D chromatography approach was developed for the separation and identification of membrane permeable compounds in a famous traditional Chinese medicine of Schisandra chinensis. The first dimensional column was the immobilized liposome chromatography (ILC) column, which mimics the biological membranes and can be used to study drug-membrane interactions in liquid chromatography. Using an automatic ten-port switching valve equipped with two sample loops, the section of the first-dimension was introduced in the second-dimension consist of a silica monolithic column. More than 40 components in Schisandra chinensis were resolved by using the developed separation system and among them 14 compounds were identified interacting with the ILC column based on their retention action, UV and mass data. With this comprehensive 2D-HPLC system, the three-dimensional chromatographic fingerprints of Schisandra chinensis were preliminarily established and processed by using principal component analysis and hierarchical clustering analysis. The obtained information can distinguish the unacceptable samples of the quality control. The result demonstrated that the 2D biochromatography system has been demonstrated to have more advantages of finding strong binding bioactive components, providing an enhanced peak capacity, good sensitivity and powerful resolution biological fingerprinting analysis of complex TCMs, which was a useful means to control the quality of and to clarify the membrane permeability of the compounds in Schisandra chinensis.
Keywords: Two-dimensional chromatography; Immobilized liposome chromatography; Mass spectrometry, Traditional Chinese medicine; Principal component analysis; Hierarchical coustering analysis;

Display Omitted► A novel log  k w evaluation protocol was proposed for the first time. ► The approach greatly simplified K ow measuring procedure for lipophilic compounds. ► Log  K ow data of 21 PCBs, PBBs and PBDEs were determined for the first time.The retention factor corresponding to pure water in reversed-phase high performance liquid chromatography (RP-HPLC), k w , was commonly obtained by extrapolation of retention factor (k) in a mixture of organic modifier and water as mobile phase in tedious experiments. In this paper, a relationship between log  k w and log  k for directly determining k w has been proposed for the first time. With a satisfactory validation, the approach was confirmed to enable easy and accurate evaluation of k w for compounds in question with similar structure to model compounds. Eight PCB congeners with different degree of chlorination were selected as a training set for modeling the log  k w  − log  k correlation on both silica-based C8 and C18 stationary phases to evaluate log  k w of sample compounds including seven PCB, six PBB and eight PBDE congeners. These eight model PCBs were subsequently combined with seven structure-similar benzene derivatives possessing reliable experimental K ow values as a whole training set for log  K ow  − log  k w regressions on the two stationary phases. Consequently, the evaluated log  k w values of sample compounds were used to determine their log  K ow by the derived log  K ow  − log  k w models. The log  K ow values obtained by these evaluated log  k w were well comparable with those obtained by experimental-extrapolated log  k w , demonstrating that the proposed method for log  k w evaluation in this present study could be an effective means in lipophilicity study of environmental contaminants with numerous congeners. As a result, log  K ow data of many PCBs, PBBs and PBDEs could be offered. These contaminants are considered to widely exist in the environment, but there have been no reliable experimental K ow data available yet.
Keywords: n-Octanol/water partition coefficient (K ow ); RP-HPLC; Brominated flame retardants (BFRs); Polychlorinated biphenyls (PCBs); Polybrominated biphenyls (PBBs); Polybrominated diphenyl ethers (PBDEs);

Highly selective solid-phase extraction of trace Pd(II) by murexide functionalized halloysite nanotubes by Ruijun Li; Qun He; Zheng Hu; Shengrui Zhang; Lijun Zhang; Xijun Chang (136-144).
Murexide functionalized halloysite nanotubes have been developed to separate and concentrate trace Pd(II) from aqueous samples. Parameters that affected the sorption and elution efficiency were studied in column mode, and the new adsorbent presented high selectivity and adsorption capacity for the solid phase extraction of trace Pd(II).Display Omitted► Murexide modified halloysite nanotubes as adsorbent has been reported originally. ► This adsorbent has a unique selectivity for Pd(II) at pH 1.0. ► This adsorbent had high adsorption capacity for Pd(II). ► The precision and accuracy of the method are satisfactory.The originality on the high efficiency of murexide modified halloysite nanotubes as a new adsorbent of solid phase extraction has been reported to preconcentrate and separate Pd(II) in solution samples. The new adsorbent was confirmed by Fourier transformed infrared spectra, X-ray diffraction, scanning electron microscope, transmission electron microscope and N2 adsorption–desorption isotherms. Effective preconcentration conditions of analyte were examined using column procedures prior to detection by inductively coupled plasma-optical emission spectrometry (ICP-OES). The effects of pH, the amount of adsorbent, the sample flow rate and volume, the elution condition and the interfering ions were optimized in detail. Under the optimized conditions, Pd(II) could be retained on the column at pH 1.0 and quantitatively eluted by 2.5 mL of 0.01 mol L−1 HCl–3% thiourea solution at a flow rate of 2.0 mL min−1. The analysis time was 5 min. An enrichment factor of 120 was accomplished. Common interfering ions did not interfere in both separation and determination. The maximum adsorption capacity of the adsorbent at optimum conditions was found to be 42.86 mg g−1 for Pd(II).The detection limit (3σ) of the method was 0.29 ng mL−1, and the relative standard deviation (RSD) was 3.1% (n  = 11). The method was validated using certified reference material, and has been applied for the determination of trace Pd(II) in actual samples with satisfactory results.
Keywords: Solid-phase extraction; Palladium(II); Halloysite nanotube; Inductively coupled plasma-optical emission spectrometry;