Simultaneous determination of peroxydisulfate and conventional inorganic anions by ion chromatography with the column-switching technique.

The application of ion chromatography with the column-switching technique for the simultaneous analysis of peroxydisulfate and conventional inorganic anions in a single run is described. With this method, conventional inorganic anions were separated by consecutive elution through both the guard column and separation column, but peroxydisulfate that only passed through the guard column had a good peak shape and short retention time. A series of standard solutions consisting of target anions of various concentrations from 0.01 to 75 mg/L were analyzed, with a correlation coefficient (r) ≥ 0.9990. The limits of detection were in the range of 0.49-9.84 µg/L based on the S/N of 3 and a 25 µL injection volume. RSDs for retention time, peak area, and peak height were all <1.77%. A spiking study was performed with satisfactory recoveries between 97.6 and 103.4% for all anions. The quantitative determination of peroxydisulfate and conventional inorganic anions in surface waters was accomplished within 18 min by this column-switching technique.

Acylated anthocyanins from Dendrobium officinale Kimura & Migo: Structural characteristics, antioxidant and hypoglycemic activities.

Dendrobium officinale Kimura & Migo (D. officinale) has been widely used as Chinese medicine and functional food. In present study, the structural characteristics of anthocyanins in D. officinale were investigated by ultra-performance liquid chromatography with diode array detector (UPLC-DAD) and ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-Q-TOF-MS/MS). Totally, 14 anthocyanins were detected and identified, and 13 of them were first reported in D. officinale. Results showed that the vast majority of anthocyanins had multi-glycosylated cyanidin core, with variable acylation pattern mainly comprising phenolic acids. The composition and content of anthocyanins in D. officinale stems with different cultivation modes and years have been compared. The anthocyanins showed potent antioxidant activity in terms of radicals scavenging capacity and reducing power, as well as superior α-amylase and α-glucosidase inhibitory activity. The results provided a complete profile of anthocyanins in D. officinale and laid a foundation for further utilizing them as functional foods.

Determination of Biogenic Amines in Wine from Chinese Markets Using Ion Chromatography-Tandem Mass Spectrometry.

A method for the determination of nine biogenic amines (BAs) in wine was established using ion chromatography-tandem mass spectrometry (IC-MS/MS) without derivatization. BAs were separated by a cation exchange column (IonPac CG17, 50 mm × 4 mm, 7 µm) with a gradient aqueous formic acid elution. Good linearity was obtained for nine BAs with coefficients of determination (R2) > 0.9972 within the range of 0.01-50 mg/L. The limits of detection and quantification were within the ranges of 0.6-40 µg/L and 2.0-135 µg/L, respectively, with the exception of spermine (SPM). The recoveries were demonstrated within the range of 82.6-103.0%, with relative standard deviations (RSDs) of less than 4.2%. This simple method featuring excellent sensitivity and selectivity was suitable for the quantification of BAs in wines. The occurrence of BAs in 236 wine samples that are commercially available in China was determined. The BA levels in wines of different geographical origins varied significantly. The acute dietary exposure assessment of BAs was carried out by calculating the estimated short-term intake (ESTI) and comparing the acute reference dose (ARfD) specified by the European Food Safety Authority (EFSA). Results showed that the exposure to histamine (HIS) and tyramine (TYR) via the consumption of wines was much lower than the recommended ARfD level for healthy individuals. However, exposure could lead to symptoms in susceptible individuals. These results provided basic data regarding the occurrence and risk of BAs in wines for wine production, health guidance and consumer safety.

Structural characteristics, functional properties, antioxidant and hypoglycemic activities of pectins from feijoa (Acca sellowiana) peel.

The structure characteristics, functional properties, antioxidant and hypoglycemic activities of pectins extracted from feijoa peel with water (FP-W), acid (FP-A) and alkali (FP-B) were investigated. Results showed that the feijoa peel pectins (FPs) were mainly composed of galacturonic acid, arabinose, galactose and rhamnose. FP-W and FP-A had higher proportion of homogalacturonan domain, degree of esterification and molecular weight (for main component) than FP-B; FP-B owned the highest yield, protein and polyphenol contents. FP-W had a compact and smooth surface morphology unlike FP-A and FP-B. FP-W and FP-A had better thermal stability than FP-B. The rheological analysis suggested that the FPs exhibited pseudoplastic fluid behavior, and the elastic characteristics were dominant. Results showed that FP-W and FP-B had superior antioxidant and hypoglycemic activities than FP-A. According to correlation analysis, monosaccharide composition, sugar ratios and degree of acetylation were chief factors affecting the functional properties, antioxidant and hypoglycemic activities of the FPs.

Chemical structure and antioxidant activity of a neutral polysaccharide from Asteris Radix et Rhizoma.

Asteris Radix et Rhizoma (AR) has been widely used as a herbal medicine for treating various symptoms and possesses a number of bioactivities. A neutral polysaccharide ARP-1 was isolated from AR with weight-average molecular weight of 214 kDa. The heteropolysaccharide ARP-1 was composed of fucose, arabinose, galactose, glucose and mannose with a molar ratio of 0.40:14.25:10.22:1.06:0.41. Linkage and NMR analysis showed that ARP-1 had a backbone containing →3,6)-ß-d-Galp-(1→ and →6)-ß-d-Galp-(1 â†’ residues, and oligosaccharide side chains containing Araf and Galp units were attached to the backbone at C-3 of →3,6)-ß-d-Galp-(1 â†’ residues. Antioxidant activity assays showed that ARP-1 exhibited potent antioxidant activities, including ABTS, hydroxy and DPPH radicals scavenging and reducing power. Besides, ARP-1 decreased the production of ROS and MDA, and improved the activities of SOD, which resulted in the protection of PC12 cells against H2O2-induced oxidative stress. The findings indicated that ARP-1 might be used as a potential natural antioxidant.

Changes in Physicochemical Properties, Volatile Profiles, and Antioxidant Activities of Black Apple During High-Temperature Fermentation Processing.

Black apple is a new elaborated product obtained from whole fresh apple through fermentation at controlled high temperature (60~90°C) and humidity (relative humidity of 50~90%). The appearance, color, texture, and taste of black apple changed dramatically compared with those of fresh apple. In this study, changes in the physicochemical and phytochemical properties, volatile profiles, and antioxidant capacity of apple during the fermentation process were investigated. Results showed that the browning intensity and color difference increased continuously during the whole 65-day fermentation process (p < 0.05). Sugars decreased in the whole fermentation process (p < 0.05), whereas the contents of organic acids increased first and then decreased with prolonged 35 days of fermentation (p < 0.05). Total polyphenol content of black apple showed an increase of 1.5-fold as that of fresh apple, whereas 12 common polyphenolic compounds present in fresh apple decreased dramatically in the whole fermentation process (p < 0.05). The analysis of flavor volatiles showed that high-temperature fermentation decreased the levels of alcohols and esters and resulted in the formation of furanic and pyranic compounds, which are the main products of Maillard reaction (MR). Antioxidant activities of black apple were enhanced compared with those of fresh apple, and results indicated that the enhancement of antioxidant activities was related to the polyphenols and products of MR.

Hollow fiber-solid phase microextraction of phthalate esters from bottled water followed by flash evaporation gas chromatography-flame ionization detection.

A solid phase microextraction coupled with flash evaporation gas chromatography method was applied to the determination of phthalate esters (PAEs). Polysulfone (PSF) hollow fiber at 1 cm length was employed as extraction element to adsorb PAEs directly. Predominant parameters including stirring velocity, salt concentration, extraction time and extraction temperature were optimized. PSF fiber with absorbed PAEs was put into a small sample cup. The extracted analytes were thermally desorbed at 300 °C in a pyrolyzer, and then entered into a column for separation. The linearity of the method was satisfactory over a concentration range of 2-1000 µg/L with the correlation coefficients r>0.99 for all analytes except dimethoxyethyl phthalate. The relative standard deviations for peak areas were below 9.5% (n = 6). The developed technique achieved high enrichment factors (280-9930 times) and low limits of detection (0.001-0.130 µg/L). The recoveries over the range of 87.0-117.7% were obtained by analyzing real spiked samples. The results demonstrated that this was a simple, environmentally friendly and accurate method for the determination of PAEs in bottled water samples.

Sugaring-out assisted liquid-liquid extraction coupled with high performance liquid chromatography-electrochemical detection for the determination of 17 phenolic compounds in honey.

In this work, a simple sugaring-out assisted liquid-liquid extraction (SULLE) method coupled with high performance liquid chromatography-electrochemical detection (HPLC-ECD) has been developed for rapid and sensitive determination of 17 phenolic compounds in honey. To achieve the maximum extraction efficiency of target analytes, several parameters, such as pH, ionic strength, extraction times and the volume of extracting solvent were optimized. Chromatographic separation was performed on a C18 column with a gradient methanol/aqueous formic acid elution, and the ECD was set at 1.0 V in oxidative mode. Under the optimal conditions, good linearity was obtained for 17 phenolic compounds with the coefficients of determination (R2) higher than 0.9986 in the range of 0.05-20 µg mL-1. The limits of detection (LODs, S/N = 3) for the 17 phenolic compounds were in the range of 0.20-1.26 µg kg-1 by ECD, 9-83 times lower than those obtained with UV detection. Satisfactory recoveries between 79.8% and 105.7% were obtained for spiked honey samples with relative standard deviations (RSD) less than 5.1%. Compared with conventional LLE method, the proposed SULLE method provided higher extraction efficiency and had advantages of rapidity, ease of operation, much less consumption of organic solvents and samples. The proposed HPLC-ECD method featuring excellent sensitivity and selectivity has been applied to the quantification of phenolic compounds in honey samples of different floral origin.

[Determination of anserine, homocarnosine and carnosine in meat products by ion chromatography with integrated pulsed amperometric detection].

A method was developed for the simultaneous determination of anserine, homocarnosine and carnosine in meat samples using ion chromatography (IC) with integrated pulsed amperometric detection (IPAD). The samples were separated on a high performance anion exchange AminoPac PA10 column (250 mm×2 mm) using 100 mmol/L NaOH as the eluent. The flow rate was kept at 0.2 mL/min and the column temperature was set at 30℃. The three target compounds were separated within 15 min, and there were no interferences from 17 tested amino acids in their determination. Under the optimal chromatographic conditions, anserine, homocarnosine and carnosine showed good linearity in the range of 0.05-5 mg/L with correlation coefficients (r) greater than 0.99. The limits of detection (LODs) and limits of quantification (LOQs) were in the range of 8.9-22.1 µg/L and 29.6-73.6 µg/L, respectively. The proposed method was applied to the analysis of duck breast and goose breast meat samples. The average spiked recoveries ranged from 92.4% to 104.5%. This simple and sensitive method can be applied to the determination of related nutrients in meat products.

Determination of γ-hydroxybutyrate in human urine samples by ion exclusion and ion exchange two-dimensional chromatography system.

A two-dimensional ion chromatography system was developed for the determination of γ-hydroxybutyrate (GHB) in human urine samples. Ion exclusion chromatography was used in the first dimensional separation for elimination of urine matrices and detection of GHB above 10mgL-1, ion exchange chromatography was used in the second dimensional separation via column-switching technique for detection of GHB above 0.08mgL-1. Under the optimized chromatographic conditions, the ion exclusion and ion exchange chromatography separation system exhibited satisfactory repeatability (RSD<3.1%, n=6) and good linearity in the range of 50-1000mgL-1 and 0.5-100mgL-1, respectively. By this method, concentrations of GHB in the selected human urine samples were detected in the range of 0-1.57mgL-1. The urine sample containing 0.89mgL-1 GHB was selected to evaluate the accuracy; the spiked recoveries of GHB were 95.9-102.8%. The results showed that the two-dimensional ion chromatography system was convenient and practical for the determination of GHB in human urine samples.

Molecular mechanisms of novel peptides from silkworm pupae that inhibit α-glucosidase.

The objectives of this study were to identify peptides that inhibit α-glucosidase using a quantitative structure-activity relationship (QSAR) screening method and a database of silkworm peptides. This study compared the docking characteristics of several peptides with high inhibitory activity against α-glucosidase and summarized the molecular mechanisms by which the silkworm peptides affected α-glucosidase. Four peptides that strongly inhibited α-glucosidase were obtained: Gln-Pro-Gly-Arg with IC50 at 65.8 µmol/L, Ser-Gln-Ser-Pro-Ala at 20 µmol/L, Gln-Pro-Pro-Thr at 560 µmol/L and Asn-Ser-Pro-Arg at 205 µmol/L. Studies docking the peptides to the active site of α-glucosidase (PDB ID: 2QMJ) showed that a common characteristic was Lys776 in 2QMJ, which could be a critical target for α-glucosidase trapping of inhibitory peptides. The results revealed that the four peptides, especially Ser-Gln-Ser-Pro-Ala, could be potential drugs for treating diabetes.

Determination of methacrylic acid in food simulants by pyrolytic butylation-gas chromatography.

An on-line pyrolytic butylation approach was proposed to determine methacrylic acid (MA) in food simulants by gas chromatography (GC) without an expensive pyrolyzer. MA in food simulants was converted into butyl methacrylate in the presence of tetrabutylammonium hydroxide (TBAH) without any pretreatment at 330°C in the injection-port, contributing to high GC signal response. The derivatizing conditions for the proposed method were optimized, namely the injection-port temperature, type and amount of the organic alkaline used for derivatization. A series of standard solutions of MA in the range of 1.0-50mg/kg were analyzed with correlation coefficient r≥0.9975. The limits of detection (LODs) were less than 0.15mg/kg for MA in four matrix simulants (distilled water, 3%w/v acetic acid, 10%v/v ethanol, and isooctane). Relative standard deviations (RSDs) for retention time, peak height and peak area were all less than 3.88%. The technique was successfully applied to the analysis of MA migrating from plastic cup samples, with recoveries of added MA in the range of 96.5-123.0%. Direct injection of the simulants into the GC system after migration tests, without any pretreatment step, makes the developed method of great value for rapid screening analysis of samples in bulks.

Molecular Mechanisms of Several Novel Dipeptides with Angiotensin-I-converting Enzyme Inhibitory Activity from In-silico Screening of Silkworm Pupae Protein.

An in silico screening method for novel dipeptides from a dipeptide training set was performed. A 3D pharmacophore model with three H-bond acceptor projections (Acc2), and one H-bond donor projection (Don2) was obtained. To validate the pharmacophore model, a test set containing 10 reported dipeptides was screened and all were found to be bioactive. Eleven novel dipeptides (IF, GD, DA, TE, TA, ES, SS, ST, SD, QD, QE) from the silkworm pupae protein peptide database were predicted to have ACE inhibitory bioactivity. The interaction mechanisms of the dipeptides with the ACE active pocket were elucidated by molecule docking, and besides involving interaction bonds, the interaction force equipoise of the peptides was also an important factor in their bioactivity.

Ion-exchange chromatography combined with direct current amperometric detection at CuNPs/reduced graphene oxide-chitosan composite film modified electrode for determination of monosaccharide composition of polysaccharides from Phellinus igniarius.

A novel Cu nanoparticles/reduced graphene oxide-chitosan (CuNPs/r-GO-chitosan) composite film modified glassy carbon electrode (GCE) was fabricated by dispersing CuNPs uniformly on a stable r-GO-chitosan thin film through electrodeposition process. The modified electrode was characterized by cyclic voltammetry, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS), and exhibited efficiently electrocatalytic oxidation toward monosaccharides with high stability. The good electrocatalytic activity of this modified electrode might be attributed to the synergistic effect of r-GO and CuNPs, and the stability might be attributed to the r-GO and chitosan thin matrix film. When the CuNPs/r-GO-chitosan/GCE was used as an electrochemical sensor in high performance anion exchange chromatography-direct current amperometric detection (HPAEC-DC) flowing system for the determination of monosaccharides under constant working potential of +0.55 V, the detection limits (S/N=3) ranged from 0.006 to 0.02 mg L(-1) for the analyzed sugars, and the dynamic linear ranges spanned from 0.02 to 500 mg L(-1). The proposed method has been applied for the determination of monosaccharide composition of crude polysaccharides from phellinus igniarius real samples, and the results were satisfactory.

A single pump cycling-column-switching technique coupled with homemade high exchange capacity columns for the determination of iodate in iodized edible salt by ion chromatography with UV detection.

A single pump cycling-column-switching technique has been developed for the iodate analysis in edible salt. Homemade high exchange capacity columns were adopted for the separation of iodate and chloride. Iodate could be retained and concentrated in a homemade concentrator column after eluents passing through the suppressor. With UV detection, iodate exhibited satisfactory linearity in the range of 0.1-10.0 mg/L with a correlation coefficient of 0.9996. The detection limit (LOD) was 45.53 µg/L, based on the signal-to-noise ratio of 3 (S/N=3) and a 100 µL injection volume. Relative standard deviations (RSDs) for retention time, peak area and peak height were all less than 2.1%. Recoveries of added iodate were in the range of 98.4-101.6% for the spiked samples. The quantitative determination of iodate in edible salt was accomplished by this column-switching technique, without any pretreatment and interference. The results on six samples were statistically compared with results determined by conventional titrimetric method.

Simultaneous determination of glucose, D-gluconic, 2-keto-D-gluconic and 5-keto-D-gluconic acids by ion chromatography-pulsed amperometric detection with column-switching technique.

A simple ion chromatographic (IC) method for simultaneous determination of glucose, D-gluconic acid (DGA), 2-keto-D-gluconic acid (2-KDG) and 5-keto D-gluconic acid (5-KDG) was proposed, with pulsed amperometric detection (PAD) and column-switching technique. Using this technique, the four compounds were detected simultaneously in a short time with strongly retained compounds (2-KDG and 5-KDG) eluted out prior to weakly retained compounds (glucose and DGA). Under the optimized conditions, the method showed good linearity in the range of 0.01-20 mg L(-1) with determination coefficients (R(2))≥ 99.84%. Low detection limits (LODs) in the range of 0.87-2.59 µg L(-1) and good repeatability (RSD<3%, n=6) were obtained. The proposed method has been successfully applied to the analysis of the four compounds in the fermentation broth, in which Gluconobacter oxydans was used to produce gluconic acids from glucose.

Simultaneous determination of imidacloprid and carbendazim in water samples by ion chromatography with fluorescence detector and post-column photochemical reactor.

A new analytical method has been developed and validated for the simultaneous determination of pesticides from different classes using ion chromatography-online photochemical derivatisation-fluorescence detector (IC-hv-FD). Fluorimetric detection was performed at λex/λem=332 nm/367 nm for imidacloprid and then detector was set at λex/λem=247 nm/470 nm for carbendazim. The two pesticides imidacloprid and carbendazim were successfully separated isocratically on an IonPac(®) AS11 (250 mm × 4 mm i.d; 13 µm particle size, Dionex) anion-exchange column using 40 mM KOH with 10% (v/v) acetonitrile and pumped at a flow rate of 1.0 mL min(-1). Under the optimized conditions, the limit of detection (LOD, S/N=3) of imidacloprid and carbendazim were 7.8 µg L(-1) and 67 µg L(-1), respectively. The experimental results showed that there was good linearity with a correlation coefficient (r)≥0.9966 over the range of 0.05-10 mg L(-1) for imidacloprid and 0.2-15 mg L(-1) for carbendazim. Good reproducibility with a relative standard deviation (RSD, n=7) less than 4.5%. Finally, the proposed method was applied with satisfactory results to the analysis of these pesticides in ground water, lake water and river water without any pre-treatment of samples. The average spiked recoveries were in the range of 90-104%.

Determination of methotrexate and folic acid by ion chromatography with electrochemical detection on a functionalized multi-wall carbon nanotube modified electrode.

A simple and sensitive method was developed for simultaneous determination of methotrexate (MTX) and folic acid (FA) by ion chromatography with electrochemical detection (IC-ECD). Quaternary amine functionalized multi-wall carbon nanotubes (q-MWNTs) modified glassy carbon electrode (GCE) was used as an amperometric sensor to determine MTX and FA. The electrochemical behaviors of MTX and FA at the q-MWNTs/GCE were studied by cyclic voltammetry (CV). Results indicated that this modified electrode exhibited electrocatalytic oxidation toward MTX and FA with high sensitivity, stability and long life. Good separation of MTX and FA was demonstrated by IC on an anion-exchange column with phosphate buffer solution (PBS) as eluent. Under the optimal conditions, the linear ranges were from 0.01 to 20mg/L for both MTX and FA with correlation coefficients r ≥ 0.9994. The obtained detection limits (LODs) for MTX and FA were 0.2 and 0.4 µg/L (S/N=3), respectively. The method has been successfully applied to the determination of MTX and FA in plasma and urine of patients of rheumatoid arthritis.

Analysis of hexavalent chromium in Colla corii asini with on-line sample pretreatment valve-switching ion chromatography.

An ion chromatography (IC) system with on-line sample pretreatment using valve-switching technique was developed for the determination of hexavalent chromium (Cr(VI)) in Colla corii asini. Colla corii asini is a complicated sample with organics as main matrix. In this work, a polymer-based reversed-phase column was used as a pretreatment column. Via valve-switching technique, sample solution with target ions were eluted from a collection loop to analytical columns, with matrix eliminated on-line. Under the optimized separation conditions, the method showed good linearity (r=0.9998) in the range of 0.004-1.0mg/L and satisfactory repeatability (RSD<3%, n=6). The limit of detection (LOD) was 1.4µg/L (S/N=3). The average spiked recoveries of Cr(VI) were 93.4-102.0%. The result showed that the on-line sample pretreatment IC system was convenient and practical for the determination of trace Cr(VI) in Colla corii asini samples.

Simultaneous determination of iodide and iodate in povidone iodine solution by ion chromatography with homemade and exchange capacity controllable columns and column-switching technique.

A simple ion chromatographic method for simultaneous detection of iodide and iodate in a single running was proposed, with columns packed with homemade functionalized polystyrene-divinylbenzene (PS-DVB) resins and column-switching technique. Homemade resins were functionalized with controllable amounts of quaternary ammonium groups. The low-capacity anion-exchange column and high-capacity anion-exchange column were prepared, due to the resins having different exchange capacities. With this method, iodide and iodate in povidone iodine solution were detected simultaneously in a short time with iodide being eluted off first. A series of standard solutions consisting of target anions of various concentrations from 0.01 mg/L to 100 mg/L were analyzed. Each anion exhibited satisfactory linearity, with correlation coefficient r ≥ 0.9990. The detection limits (LODs) for iodide and iodate obtained by injecting 100 µL of sample were 5.66 and 14.83 µg/L (S/N=3), respectively. A spiking study was performed with satisfactory recoveries between 101.2% and 100.6% for iodide and iodate.