Analytica Chimica Acta (v.877, #C)

Quantitative determination of fucoidan using polyion-sensitive membrane electrodes by Ji Min Kim; Loc Nguyen; Mary Frances Barr; Michael Morabito; Damien Stringer; J. Helen Fitton; Kelly A. Mowery (1-8).
Display OmittedThe use of polyanion and polycation-sensitive membrane electrodes to detect five different preparations of fucoidan is described. Unlike linear polyanionic molecules previously measured with polymer membrane-based electrochemical sensors, fucoidans from marine brown algae are all highly branched, sulfated polysaccharides with varying charge densities and structures, depending on the species of seaweed, method of extraction used and extent of purification. When tridodecylmethylammonium (TDMA) was used as the ion-exchanger, a large, non-equilibrium EMF response was observed over a concentration range of 0.5–50 μg mL−1 fucoidan. Fucoidan was also measured by titration with polycationic protamine, using a dinonylnaphthalene sulfonate (DNNS)-doped membrane electrode as the potentiometric endpoint detector. Potentiometric titration was used to determine the binding ratio between protamine and fucoidan at the neutralization endpoint for each fucoidan preparation. This binding ratio was then used to successfully determine the fucoidan content of commercially available nutritional supplements. Fucoidan was also measured in undiluted blood serum, demonstrating that this method may be applicable for measuring fucoidan for clinical applications.
Keywords: Fucoidan; Polyion-sensitive electrode; Potentiometric titration; Potentiometry;

Display OmittedIn contrast to the existence of standardized methods to assess metal bioaccessibility via the gastrointestinal route, there are no widely-accepted, established in vitro testing protocols to measure elemental solubility in the human lung. This may be attributed, in part, to the difficulty associated with simulating the lung’s complex in vivo conditions. The purpose of this review is two-fold: (1) to determine how the bioaccessibility of metals associated with ambient particulate matter (PM) in the human lung has been assessed in the literature, and (2) examine the suitability and biological relevance of applied methods for the measurement of metal bioaccessibility employed to date.The review revealed that limited attention has been paid to the development and application of biologically-relevant in vitro methods to measure elemental solubility in ambient PM as a proxy for bioaccessibility in the human lung. Few studies (n  = 14) used synthetic lung fluids to simulate in vivo conditions, with only half extracting samples at a biologically-relevant temperature of 37 °C. There was limited evidence suggesting that the use of water is less effective as a leaching agent compared to simulated lung fluids. In sum, this scoping review highlights a critical need to develop standardized methods for the systematic assessment of elemental bioaccessibility via the respiratory route. Priority should be placed on the validation of biologically-relevant methods, including the use of leaching agents and extraction parameters used, which allow for testing to be conducted in a reliable, yet cost efficient, manner.
Keywords: Airborne particulate matter; Bioaccessibility; Metals; Simulated lung fluids; In vitro methods;

Display OmittedDemand is increasing for ultrasensitive bioassays for disease diagnosis, environmental monitoring and other research areas. This requires novel signal amplification strategies to maximize the signal output. In this review, we focus on a series of significant signal amplification strategies based on polymeric nanocomposites and polymerization. Some common polymers are used as carriers to increase the local concentration of signal probes and/or biomolecules on their surfaces or in their interiors. Some polymers with special fluorescence and optical properties can efficiently transfer the excitation energy from a single site to the whole polymer backbone. This results in superior fluorescence signal amplification due to the resulting collective effort (integration of signal). Recent polymerization-based signal amplification strategies that employ atom transfer radical polymerization (ATRP) and photo-initiated polymerization are also summarized. Several distinctive applications of polymers in ultrasensitive bioanalysis are highlighted.
Keywords: Signal amplification; Biosensor; Polymerization; Polymeric DNA dendrimers; Conjugated polymers; Atom transfer radical polymerization;

Analytical potential of a laser ablation–glow discharge–optical emission spectrometry system for the analysis of conducting and insulating materials by Claudia González de Vega; Cesar Álvarez Llamas; Nerea Bordel; Rosario Pereiro; Alfredo Sanz-Medel (33-40).
Display OmittedThe analytical capabilities of a glow discharge (GD) as a secondary source for excitation/ionization of the material provided by laser ablation (LA) have been compared to conventional laser induced breakdown spectroscopy (LIBS). In LA–GD both sources can be independently adjusted to optimize the sampling process and then its subsequent excitation. This could involve a number of analytical performance advantages, such as reduced matrix dependence, greater precision and sensitivity than those encountered in LIBS. For such purpose, an ablation chamber design including two electrodes to generate the GD discharge has been built and assayed. A comparison between LIBS and LA–GD–OES has been carried out, both, under reduced argon and helium atmospheres. Different sets of samples (conducting reference materials, glass and fluorine pellets) have been used to evaluate the novel coupled technique. The LA–GD coupled system has shown to provide lower detection limits. In addition, best linear correlations between intensities and concentrations and lower matrix effects have also been found using the coupled system. Moreover, special advantages of the LA–GD–OES have also been demonstrated for the analysis of fluorine.
Keywords: Glow discharge; Laser induced breakdown spectroscopy; Optical emission spectrometry; Fluorine analysis;

Discrimination and classification techniques applied on Mallotus and Phyllanthus high performance liquid chromatography fingerprints by J. Viaene; M. Goodarzi; B. Dejaegher; C. Tistaert; A. Hoang Le Tuan; N. Nguyen Hoai; M. Chau Van; J. Quetin-Leclercq; Y. Vander Heyden (41-50).
Mallotus and Phyllanthus genera, both containing several species commonly used as traditional medicines around the world, are the subjects of this discrimination and classification study. The objective of this study was to compare different discrimination and classification techniques to distinguish the two genera (Mallotus and Phyllanthus) on the one hand, and the six species (Mallotus apelta, Mallotus paniculatus, Phyllanthus emblica, Phyllanthus reticulatus, Phyllanthus urinaria L. and Phyllanthus amarus), on the other. Fingerprints of 36 samples from the 6 species were developed using reversed-phase high-performance liquid chromatography with ultraviolet detection (RP-HPLC-UV). After fingerprint data pretreatment, first an exploratory data analysis was performed using Principal Component Analysis (PCA), revealing two outlying samples, which were excluded from the calibration set used to develop the discrimination and classification models. Models were built by means of Linear Discriminant Analysis (LDA), Quadratic Discriminant Analysis (QDA), Classification and Regression Trees (CART) and Soft Independent Modeling of Class Analogy (SIMCA). Application of the models on the total data set (outliers included) confirmed a possible labeling issue for the outliers. LDA, QDA and CART, independently of the pretreatment, or SIMCA after “normalization and column centering (N_CC)” or after “Standard Normal Variate transformation and column centering (SNV_CC)” were found best to discriminate the two genera, while LDA after column centering (CC), N_CC or SNV_CC; QDA after SNV_CC; and SIMCA after N_CC or after SNV_CC best distinguished between the 6 species. As classification technique, SIMCA after N_CC or after SNV_CC results in the best overall sensitivity and specificity.
Keywords: Chromatographic fingerprinting; Supervised and unsupervised data analysis; Discrimination and classification techniques; Herbal extracts;

Procrustes rotation as a diagnostic tool for projection pursuit analysis by Peter D. Wentzell; Siyuan Hou; Carolina Santos Silva; Chelsi C. Wicks; Maria Fernanda Pimentel (51-63).
Display OmittedProjection pursuit (PP) is an effective exploratory data analysis tool because it optimizes the projection of high dimensional data using distributional characteristics rather than variance or distance metrics. The recent development of fast and simple PP algorithms based on minimization of kurtosis for clustering data has made this powerful tool more accessible, but under conditions where the sample-to-variable ratio is small, PP fails due to opportunistic overfitting of random correlations to limiting distributional targets. Therefore, some kind of variable compression or data regularization is required in these cases. However, this introduces an additional parameter whose optimization is manually time consuming and subject to bias. The present work describes the use of Procrustes analysis as diagnostic tool that can be used to evaluate the results of PP analysis in an efficient manner. Through Procrustes rotation, the similarity of different PP projections can be examined in an automated fashion with “Procrustes maps” to establish regions of stable projections as a function of the parameter to be optimized. The application of this diagnostic is demonstrated using principal components analysis to compress FTIR spectra from ink samples of ten different brands of pen, and also in conjunction with regularized PP for soybean disease classification.
Keywords: Exploratory data analysis; Projection pursuit; Procrustes analysis; Classification; Data visualization; Cluster analysis; Variable compression;

Display OmittedThis paper reports an electrochemically grown film consisting of layered MnO2 intercalated with hexadecylpyridinium cations (HDPy+), which can selectively sorb and detect iodide anions in aqueous solution amperometrically. Sorption of iodide by the HDPy/MnO2 film did not occur via ion exchange, but through hydrophobic interactions between the interlayer organic phase of the film and iodide ions in solution. The sorption rate increased with the deposited amount of MnO2. During the sorption process, the interlayer spaces expanded, and new diffraction peaks appeared that were attributed to the incorporated species. Anodic polarization of the iodide-sorbed HDPy/MnO2 film led to electron transfer from the incorporated iodide to the underlying substrate through the MnO2 sheets. The oxidized iodide was expelled from the film as molecular I2, while the expanded interlayer spaces were restored to their original state. Thus, the MnO2 layers and the incorporated HDPy can synergistically sorb/desorb iodide anions, resulting in a unique “self-cleaning” function that can operate electrochemically. This property allowed amperometric detection of iodide at a concentration as low as 0.0186 μM, which was below the detection limits reported for previous iodide sensors.
Keywords: Manganese dioxide; Hexadecylpyridinium; Iodide; Sorption/desorption; Thin film; Sensing;

Textile-based sampling for potentiometric determination of ions by Grzegorz Lisak; Thomas Arnebrant; Tautgirdas Ruzgas; Johan Bobacka (71-79).
Display OmittedPotentiometric sensing utilizing textile-based micro-volume sampling was applied and evaluated for the determination of clinically (Na+, K+, Cl) and environmentally (Cd2+, Pb2+ and pH) relevant analytes. In this technological design, calibration solutions and samples were absorbed into textiles while the potentiometric cells (ion-selective electrodes and reference electrode) were pressed against the textile. Once the liquid, by wicking action, reached the place where the potentiometric cell was pressed onto the textile, hence closing the electric circuit, the potentiometric response was obtained. Cotton, polyamide, polyester and their blends with elastane were applied for micro-volume sampling. The textiles were found to influence the determination of pH in environmental samples with pH close to neutral and Pb2+ at low analyte concentrations. On the other hand, textile-based micro-volume sampling was successfully applied in measurements of Na+ using solid-contact sodium-selective electrodes utilizing all the investigated textiles for sampling. It was found that in order to extend the application of textile-based sampling toward environmental analysis of ions it will be necessary to tailor the physio-chemical properties of the textile materials. In general, textile-based sampling opens new possibilities for direct chemical analysis of small-volume samples and provide a simple and low-cost method to screen various textiles for their effects on samples to identify which textiles are the most suitable for on-body sensing.
Keywords: Textile-based sampling; Potentiometric determination of ions in clinical and environmental samples; Non-invasive wearable potentiometric sensors;

Display OmittedMolecularly imprinted polymer (MIP) was synthesized and applied for the extraction of chicoric acid from Chicory herb (Chicorium intybus L.). A computational study was developed to find a suitable template to functional monomer molar ratio for MIP preparations. The molar ratio was chosen based on the comparison of the binding energy of the complexes between the template and functional monomers. Based on the computational results, eight different polymers were prepared using chicoric acid as the template. The MIPs were synthesized in a non-covalent approach via thermal free-radical polymerization, using two different polymerization methods, bulk and suspension. Batch rebinding experiments were performed to evaluate the binding properties of the imprinted polymers. The best results were obtained with a MIP prepared using bulk polymerization with 4-vinylpyridine (4-VP) as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the crosslinker with a molar ratio of 1:4:20. The best MIP showed selective binding ability toward chicoric acid in the presence of the template’s structural analogues, caffeic acid, caftaric acid and chlorogenic acid.
Keywords: Molecularly imprinted polymer; Computational study; Extraction; Phenolic acids; Chicoric acid;

Magnetic graphene oxide modified with choline chloride-based deep eutectic solvent for the solid-phase extraction of protein by Yanhua Huang; Yuzhi Wang; Qi Pan; Ying Wang; Xueqin Ding; Kaijia Xu; Na Li; Qian Wen (90-99).
Display OmittedFour kinds of green deep eutectic solvents (DESs) based on choline chloride (ChCl) have been synthesized and coated on the surface of magnetic graphene oxide (Fe3O4@GO) to form Fe3O4@GO-DES for the magnetic solid-phase extraction of protein. X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Fourier transform infrared spectrometry (FTIR), field emission scanning electron microscopy (FESEM) and thermal gravimetric analysis (TGA) were employed to characterize Fe3O4@GO-DES, and the results indicated the successful preparation of Fe3O4@GO-DES. The UV–vis spectrophotometer was used to measure the concentration of protein after extraction. Single factor experiments proved that the extraction amount was influenced by the types of DESs, solution temperature, solution ionic strength, extraction time, protein concentration and the amount of Fe3O4@GO-DES. Comparison of Fe3O4@GO and Fe3O4@GO-DES was carried out by extracting bovine serum albumin, ovalbumin, bovine hemoglobin and lysozyme. The experimental results showed that the proposed Fe3O4@GO-DES performs better than Fe3O4@GO in the extraction of acidic protein. Desorption of protein was carried out by eluting the solid extractant with 0.005 mol L−1 Na2HPO4 contained 1 mol L−1 NaCl. The obtained elution efficiency was about 90.9%. Attributed to the convenient magnetic separation, the solid extractant could be easily recycled.
Keywords: Choline chloride-based deep eutectic solvent; Magnetic graphene oxide; Protein; Magnetic solid-phase extraction;

Response surface methodology toward the optimization of high-energy carotenoid extraction from Aristeus antennatus shrimp by Thalia Tsiaka; Panagiotis Zoumpoulakis; Vassilia J. Sinanoglou; Constantinos Makris; Georgios A. Heropoulos; Antony C. Calokerinos (100-110).
Display OmittedHigh-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE.Response surface methodology (RSM) is used for the optimization of extraction methodologies, also being applied to optimize high energy techniques. Three independent variables, namely extraction time, ultrasound or microwave power and solvent/material ratio, were investigated for both methods by employing a 16-run three-level Box–Behnken design (BBD). Considering the extraction efficiency for carotenoids from Aristeus antennatus shrimp, the selected conditions for UAE were 5 min, 600 W and 10:1 mL g−1. Acetone was the solvent of choice for the extraction procedure. For MAE, the best experimental values were 7 min, 30 W and 20:1 mL g−1 using n-hexane:acetone:ethanol 2:1:1 (v/v/v) as extraction solvent. The determination of total carotenoid yield was carried out using the spectophotometric calibration curve (A  = 0.1646(±0.0061)C  − 0.005(±0.022), R 2  = 0.996, n  = 3) of a standard mix solution of canthaxanthin, zeaxanthin and lutein at 452.1 nm. Under the selected conditions, the yield of total carotenoids for UAE was 23.4(±2.3) and 6.73(±0.56) mg of carotenoids per 100 g dry sample for the head and the body of shrimp, while for MAE was 23.92(±0.63) and 13.3(±1.1) mg of carotenoids per 100 g dry sample, respectively. The recovery of both methods was calculated between 60 and 105%. The results indicate that high-energy extraction techniques are faster, less laborious, more repeatable and reproducible methods than the conventional approaches for the quantitative recovery of sensitive bioactive compounds. Moreover, the recovery of a high-added value group of bioactive molecules from natural sources, such as carotenoids, can constitute a profitable and valuable commercial alternative, as these compounds can be used as dietary supplements, food color enhancers and additives in animal feeds, functional foods, preservatives, pharmaceuticals and cosmetics.
Keywords: Ultrasound-assisted extraction; Microwave-assisted extraction; Carotenoids; Response surface methodology; Box–Behnken design;