Determination of Oxolinic Acid Residues in Gilthead Seabream (Sparus aurata) Muscle Tissue and Plasma by High-Performance Liquid Chromatography

A high-performance liquid chromatographic method for the determination of oxolinic acid (OA) residues in muscle tissue and plasma of the cultured fish gilthead seabream (Sparus aurata L.), is described. OA was extracted with ethyl acetate and after centrifugation the combined extracts were evaporated. To the remaining residue 1 mL of the mobile phase was added and the extract was partitioned with n-pentane which then was rejected by aspiration. OA was chromatographed on a Zorbax^®SB-C₁₈ column at 50^oC and detected by fluorescence detection at λ_ex 327 nm and λ_em 369 nm. The mobile phase was a mixture of 0.1% trifluoroacetic acid (v/v) pH 2.0 and acetonitrile-methanol 3:2 (v/v) in a combination of 50:50 (v/v) and a flow rate of 1.0 mL min^?1, delivered isocratically. Method mean recovery (R%) achieved was 73.7 ± 4.4% (mean ± SD) for blank fortified samples (n=4) range at 50, 100 and 200 μg kg^?1 with a RSD=3.3%. The limit of detection (LOD) was 2.0 μg kg^?1 oxolinic acid in muscle tissue and plasma and the limit of quantification (LOQ) was 5.0 μg kg^?1. The method is fast and suitable to be used with safety and accuracy for the control of OA residues in cultured seabreams and a trained analyst could carry out ready for chromatography more than 50 samples per working day.     

Determination of Levamisole in Sheep Muscle Tissue by High-Performance Liquid Chromatography and Photo Diode Array Detection

A high-performance liquid chromatographic method for the determination of levamisole (LVM) residues in sheep muscle tissue is described. LVM was extracted with ethyl acetate under alkaline conditions and cleanup was performed by liquid-liquid partition between organic-basic and organic-acid medium. Finally, levamisole was back extracted with chloroform carefully transferred into a clean glass vial and evaporated to dryness at 50 °C under a gentle stream of nitrogen. The remaining dry residue was dissolved in the mobile phase used, filtered and an aliquot was injected automatically into the chromatograph for analysis. Chromatography was performed on a Zorbax^?SB-C₁₈ column at 50 °C and detection by a PDA detector monitored at λ_max 220 nm. The mobile phase was a mixture of 0.1 % trifluoroacetic acid (v/v) pH 2.0 and acetonitrile-methanol 3 : 2 (v/v) in a combination of 30 : 70 (v/v) and a flow rate of 1.0 mL min⁻¹, delivered isocratically. This analytical method was validated by assessing recovery efficiency using spiked muscle tissue samples with standard solutions in methanol at four fortification levels of 1/2 MRL, 1 MRL, 2 MRL and 4 MRL and five times for each concentration (n = 5). Mean recovery (R%) achieved for muscle tissue was 75.65 ± 2.74% with an acceptable Relative Standard Deviation RSD% = 10.4. The same method was used also for the analysis of kidney, liver and fat (perirenal) and the recoveries found were 70.25 ± 1.07% (RSD% = 1.52), 72.37 ± 3.6% (RSD% = 4.97) and 69.44 ± 2.22% (RSD% = 3.19), respectively. The limit of detection (LOD) for muscle tissue was found to be 2.0 μg kg⁻¹ and the limit of quantification (LOQ) 5.0 μg kg⁻¹. Revised: 4 and 24 January 2006     

A catechol electrode based on spinach leaves

Minced spinach leaf (Spinacea oleracea) has a high activity of catechol oxidase (dimerizing) (EC 1.1.3.14), which is utilized for the determination of catechol by coupling the spinach tissue with a Clark oxygen electrode. The calibration graph for catechol is linear over the range 2×10^?5–8×10^?4 M (RSD 3%). The sensor retains its enzyme activity for at least 18 days. 4-Methylcatechol and glycolate interfere; glucose and ascorbate do not.     

Physicochemical properties and mixed electronic and ionic conduction of composite ceramics in the system ZrO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

Composites ZrO₂-(Bi₂CuO₄+ 20 wt % Bi₂O₃) (50–80 vol % ZrO₂) are synthesized and their physicochemical properties are studied. It is demonstrated that the composites comprise triple-phase mixtures of ZrO₂ of a monoclinic modification, Bi₂CuO₄, and solid solution Bi_2?x Zr _x O_{3 + x/2} and retain their mechanical strength up to 800°C. Impedance spectroscopy is used to examine their electroconductivity at 700–800°C in the interval of partial oxygen pressures extending from 37 to 2.1 × 10⁴ Pa. Contributions made by electronic and ionic constituents to their overall conductivity are evaluated. The best specimens’ conductivity is ～0.01 S cm^?1, with the electronic and ionic transport numbers nearly equal. The composite consisting of 50 vol % ZrO₂ and 50 vol % (Bi₂CuO₄ + 20 wt % Bi₂CuO₄) is tested in the role of an oxygen-separating membrane. The selective flux of oxygen in the temperature interval 750–800°C amounts to (2.2–6.3) × 10^?8 mol cm^?2 s^?1, testifying that these materials may be used as gas-separating membranes.     

Grape tissue-based electrochemical sensor for the determination of hydrogen peroxide

The use of grape tissue as a source of catalase for the determination of hydrogen peroxide is reported. A slice of grape tissue attached to the membrane of a Clark-type oxgen sensor was used to monitor the oxidation of hydrogen peroxide by catalase. At the steady state, the sensor responds linearly to hydrogen peroxide in the concentration range 1 × 10^?5–5 × 10^?4 M. The response time (T₉₀) was of the order of 1 min for this sensor. No interference was observed from ethanol, amino acids, glucose and lactic acid. The long-term stability of the grape tissue sensor was much better than previously reported immobilized enzyme and liver tissue-based hydrogen peroxide sensors.     

Stability-Indicating RP-HPLC Method for Simultaneous Determination of Metformin Hydrochloride and Sitagliptin Phosphate in Dosage Forms

A new stability-indicating high-performance liquid chromatographic method has been developed for simultaneous analysis of metformin hydrochloride (MET) and sitagliptin phosphate (SIT) in pharmaceutical dosage forms. Chromatographic separation was achieved on a C₈ column. The mobile phase was methanol–water 45:55 % (v/v) containing 0.2 % (w/v) n-heptanesulfonic acid and 0.2 % (v/v) triethylamine; the pH was adjusted to 3.0 with orthophosphoric acid. The flow rate was 1 mL min^?1 and the photodiode-array detection wavelength was 267 nm. The linear regression coefficients for metformin and sitagliptin were 0.9998 and 0.9996 in the concentration ranges 50–450, and 10–150 μg mL^?1, respectively. The relative standard deviations for intra and inter-day precision were below 1.5 %. The drugs were subjected to a variety of stress conditions—acidic and basic hydrolysis, and oxidative, photolytic, neutral, and thermal degradation. The products obtained from photolytic degradation were similar to those from neutral hydrolytic degradation and different from produced by acidic and basic hydrolysis. The method resulted in detection of 15 degradation products (D1–D15); among these, the structures of D1, D3, D9, and D13 were identified. The respective mass balance for MET and SIT was found to be close to 97.60 and 99.12 %. The specificity of the method is suitable for a stability-indicating assay.     

Determination of fluorine in geological materials by fast neutron activation based on the 19F(n,2n)18F reaction

The determination of fluorine in geological materials by fast neutron activation analysis based on the ¹⁹F(n, 2n)¹⁸F reaction is described. Fast neutrons are produced by irradiation of a thick beryllium target with 14.5 MeV deuerons. A rotating smple holder allows simultaneous irradiation of samples and standards. Fluorine-18 is separated by steam distillation of hexafluorosilicic acid or by extraction with triphenylatimony(V) dichloride and the annihilation radiation is measured with γ—γ coincidence equipment. The nuclear interference of recoil protons that induce the ¹⁸O(p,n)¹⁸F reaction is evaluated by means of synthetic samples: for a rock containing 43.4% of oxygen and 0.5% of hydrogen, the interference corresponds to 4.4 μg g^?1 fluorine. The method was applied to USGS and NIMROC reference rocks: for concentrations between 6000 and 50 μg g^?1, the relative standard deviation ranged from 2 to 10%.     

Development of an effective extraction process for coenzyme Q10 from Artemia

A method for extracting coenzyme Q₁₀ (CoQ₁₀) from Artemia was developed. 1 g of fresh Artemia was incubated with 75 % acetic acid at (30 ± 2)°C for 24 h, followed by three consecutive extractions with a mixture of 5 mL of hexane and 5 mL of ethanol, then analysis by a validated high-performance liquid chromatography with a diode-array detector. The calibration curve for CoQ₁₀ was linear in a range of 1–50 μg mL^?1. The limits of detection and quantification were 0.3 μg mL^?1 and 1.1 μg mL^?1, respectively. Mean recoveries were 94–100 % with a high precision of below 10 %. The method developed was found to be simple, efficient and the time required for releasing CoQ₁₀ from Artemia was short. The method provides not only low energy consumption but is also practical for industrial applications.     

Determination of phthalate esters in edible oils by use of QuEChERS coupled with ionic-liquid-based dispersive liquid–liquid microextraction before high-performance liquid chromatography

A selective and low organic-solvent-consuming method of sample preparation combined with high-performance liquid chromatography with diode-array detection is introduced for analysis of phthalic acid esters in edible oils. Sample treatment involves initial liquid–liquid partitioning with acetonitrile, then QuEChERS cleanup by dispersive solid-phase extraction with primary secondary amine as sorbent. Preconcentration of the analytes is performed by ionic-liquid-based dispersive liquid–liquid microextraction, with the cleaned-up extract as disperser solvent and 1-hexyl-3-methylimidazolium hexafluorophosphate as extraction solvent. Under the optimized conditions, correlation coefficients (r) were 0.998–0.999 and standard errors (S _y/x ) were 2.67–3.37?×?10³ for calibration curves in the range 50–1000 ng g^?1. Detection limits, at a signal-to-noise ratio of 3, ranged from 6 to 9 ng g^?1. Intra-day and inter-day repeatability, expressed as relative standard deviation, were in the ranges 1.0–6.9 % and 2.4–9.4 %, respectively. Recovery varied between 84 % and 106 %. The developed method was successfully used for analysis of the analytes in 28 edible oils. The dibutyl phthalate content of four of the 28 samples (14 %) exceeded the specific migration limit established by domestic and international regulations.

Spectrofluorimetric method for the determination of uric acid in human serum

A new spectrofluorimetric method is described for the determination of uric acid (UA), that can remarkably reduce the fluorescence intensity of the enoxacin (ENX)-terbium ion (Tb³⁺) complex at 545 nm. The reduced fluorescence intensity of Tb³⁺ ion at pH 5.7 is proportional to the concentration of UA. Optimum conditions for the determination of UA have been investigated. The linear range and detection limit for the determination of UA are 6.0 × 10^?7–3.0 × 10^?5 M and 1 × 10^?7 M, respectively. The relative standard deviation (RSD) was 0.4% for 6 × 10^?6 M UA (n = 11). The method is simple, practical and relatively free of interferences. It has been successfully applied to assess UA in serum at the level of 3 × 10^?4 M with an RSD of 5–7% (n = 3). The results were evaluated by comparison with a common clinical spectrophotometric method using phosphotungstic acid as developer.     

Optical-fiber sensor based on the second-harmonic emission of a near-infrared semiconductor laser as light source

Second-harmonic emission from a near-infrared semiconductor laser is used as the light source for fluorimetry. The efficiency of the second-harmonic generation is 2.5×10^?6; at 390 nm, the power achieved is 50 nW when a 20-mW semiconductor laser (780 nm) is used. For fluorimetric determination of 7-diethylamino-4-methylcoumarin, the calibration plot is linear in the range 0–8×10^?7 M, the detection limit being 5×10^-∞ M (S/N=3 ). The generated ultraviolet emission is used with benzo (ghi)perylene in an optical-fiber sensor for oxygen (0–15%).     

Animal Bone Char Solubilization with Itaconic Acid Produced by Free and Immobilized Aspergillus terreus Grown on Glycerol-Based Medium

Cells of Aspergillus terreus, free and immobilized in polyurethane foam, were employed in itaconic acid fermentation processes on glycerol-based media. The purpose was to assess their suitability for animal bone char solubilization and the development of a biotechnological alternative to P fertilizers chemically produced from rock phosphate. Animal bones constitute a renewable source of P that can replace the traditionally used finite, nonrenewable rock phosphate as a P source. Glycerol was an excellent substrate for growth (10.2 g biomass L^?1) and itaconic acid production (26.9 g?L^?1) by free fungal cells after 120-h fermentation. Simultaneously, A. terreus solubilized the insoluble phosphate to a yield of 23 to 50 %, depending on the particle size and concentration. Polyurethane foam cut into cubes of 0.5–0.6 cm per side, with 0.3 mm pore size and applied at 2.0 g?L^?1 proved to be an excellent cell carrier. In repeated batch fermentation, the immobilized mycelium showed a high capacity to solubilize animal bone char, which resulted on average in 168.8 mg?L^–1 soluble phosphate per 48-h cycle and 59.4 % yield (percent of total phosphate) registered in the fourth batch.     

496—Cyclic voltammetric studies on the application of carbon elctrodes in the determination of oxalic acid

The application of carbon paste and glassy carbon electrodes in the analysis of oxalic acid was investigated by comparing the characteristics of cyclic voltammograms of oxalic acid obtained in various supporting electrolytes (acetate, borate, citrate, phosphate, etc.). When a semi-micro carbon paste electrode (area 0.49 cm²) was used, the oxalic acid was oxidized at +1.0 to +1.2 V vs Ag|AgCl yielding current in the μA range (scan rate 50 mV/s) for oxalic acid concentration of approximately 10^?4M. Oxalic acid oxidation was observed under both acidic and alkaline conditions. The presence of chloride ions or oxygen did not have any deleterious effect on the electrode response. The peak current was reproducible for repeated scans obtained with the same electrode after brief stirring. The glassy carbon electrode was found to be less suitable for oxalic acid oxidation studies because the peaks in the voltammograms were poorly defined and the current response was markedly reduced. These investigations suggest that carbon paste electrodes are sensitive and stable for oxalic acid oxidation studies. A plot of the peak currents obtained with carbon paste electrode for different concentrations of oxalic acid between 1×10^?4M to 1×10^?3M was linear and reproducible. It is suggested that a flow through carbon paste electrode coupled to a chromatographic column can be used in the development of a sensitive method for oxalic acid analysis in biological samples.     

Determination of Tangeretin in Rat Plasma by LC-Electrospray-Ion Trap MS

A selective, sensitive, and accurate method has been developed and validated for the quantification of tangeretin in rat plasma. The application of LC-electrospray-ion trap mass spectrometry in full scan and multiple reactions monitoring modes were investigated. Following solid phase extraction using a hydrophilic–lipophilic balance cartridge, the analytes were separated on a C₁₈ column using an isocratic mobile phase composed of acetonitrile/water (50:50, v/v) containing 0.3% formic acid. In full scan mode, the LOQ was 2 ng mL^?1. The standard calibration curve was linear (R ² = 0.9999) over the concentration range 2–200 ng mL^?1. The precision over the concentration range was within 15% (RSD) and the accuracy was ranged from 86 to 115%. In multiple reaction monitoring mode, the LOQ was 1 ng mL^?1 and the standard calibration curve was linear (R ² = 0.9976) over the concentration range 1–100 ng mL^?1 with a precision of 12% and accuracy rangeing from 91 to 113%.     

Development and Validation of an Improved LC Method for the Simultaneous Determination of Pirfenidone and Its Carboxylic Acid Metabolite in Human Plasma

A sensitive and specific assay based on liquid chromatography with ultraviolet detection was developed for the simultaneous determination of pirfenidone (PFD), a novel antifibrotic agent, and its carboxylic acid metabolite in human plasma. The carboxylic acid metabolite was further identified by mass spectrometric analysis. PFD, its carboxylic acid metabolite and the internal standard methyl-p-aminobenzoate were extracted from plasma by a simple one-step liquid-liquid extraction with ethyl acetate and subsequently separated on a Zorbax SB-C18 column with a mobile phase of trifluoroacetic acid–triethylamine–acetonitrile–water (0.1:0.15:28:71.75, v/v/v/v) and monitored at 314 nm. Extraction recovery was over 70% in plasma. The calibration curves were linear over the concentration range of 0.05–25 μg mL^?1. The limit of detection (LOD) and lower limit of quantitation (LLOQ) in human plasma were 10 and 50 ng mL^?1, respectively. Intra- and inter-assay precision of the method were within 8.6%. The accuracy as expressed by the bias ranged between ?4.5 and 4.0%. The method was successfully applied to determine pharmacokinetic parameters of PFD and its carboxylic acid metabolite after a single oral dose of 200 mg of PFD in healthy volunteers.     

Isolation of Chlorogenic Acid from <Emphasis Type="Italic">Flaveria bidentis</Emphasis> (L.) Kuntze by CCC and Synthesis of Chlorogenic Acid-Intercalated Layered Double Hydroxide

Preparative counter-current chromatography (CCC) was successfully used for isolation and purification of chlorogenic acid from Flaveria bidentis (L.) Kuntze with a solvent system composed of ethyl acetate–methanol–water at a volume ratio of 50:1:50, v/v. Using a preparative unit of the CCC centrifuge, about 800 mg of the crude extract was separated, yielding 3.2 mg of chlorogenic acid at a purity of 92.0%. The blood pressure lowering and antivirus chlorogenic acid (C₁₆H₁₈O₉) was intercalated into magnesium–aluminum–layered double hydroxides, which was used as host materials for drug-LDH host-guest supermolecular structures by anion exchange under a nitrogen atmosphere. Chlorogenic acid–LDH is a functional and effective drug. The product chlorogenic acid–LDH has been characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA) and scanning electron micrographs (SEM). The X-ray diffraction patterns of NO₃ ^? form of LDH and chlorogenic acid–LDH were compared, and the basal d spacing value of NO₃ ^?-LDH layer was 8.75 Å (2θ = 10.100°); however, the basal reflection (003) of chlorogenic acid–LDH shifts to lower 2θ (for 003 reflection: 2θ = 5.119°) that is expanded to 17.25 Å, indicating the intercalation of chlorogenic acid into the interlayer of Mg–Al-LDH. Thermogravimetric analysis showed that chlorogenic acid stability had improved, and scanning electron micrographs showed that the morphology of the chlorogenic acid–LDH was irregular masses of distinctly thicker flakes, which was similar to the morphology of NO₃ ^? form of LDH.     

LC Method for Quantification of ent-11α-Hydroxy-15-oxo-kaur-16-en-19-oic Acid in Rabbit Plasma: Validation and Application to a Pharmacokinetic Study

ent-11α-Hydroxy-15-oxo-kaur-16-en-19-oic acid (5F), a diterpenoid isolated from the Chinese herb Pteris semipinnata L, has been suggested to show antitumor properties. A simple and sensitive LC method was developed for the determination of 5F in rabbit plasma. The method involved liquid–liquid extraction using ethyl acetate under acidic conditions using naproxen as an internal standard. Separations were performed on a reversed-phase column with a mixture of 1% (v/v) glacial acetic acid and methanol (45:55, v/v) as mobile phase and UV detection was utilized at 242 nm. The calibration plot was linear in the range 0.20–10.0 μg mL^?1 (correlation coefficients r ²  > 0.998). The detection limit was 0.20 μg mL^?1, mean extraction recovery was above 82%, intra-day precision of the method was less than 6.4%, and inter-day precision was better than 8.7%, respectively. The validated assay was found to be suitable for the pharmacokinetic study of 5F in rabbits.     

Simultaneous Analysis of Zofenopril and Its Active Metabolite Zofenoprilat in Human Plasma by LC–ESI-MS Using Pre-Column Derivatization with p-Bromophenacyl Bromide

Zofenoprilat is an active metabolite of zofenopril, which is very unstable in plasma because of oxidative degradation of its thiol group. In this method, p-bromophenacyl bromide was used as derivatization reagent, immediately after plasma separation, to react with the free thiol group of zofenoprilat and form the derivative zofenoprilat-p-BPB. After acidification with 50% acetic acid, the derivatized plasma samples were extracted with methyl tert-butyl ether and separated on a C₁₈ column with 40:60 (v/v) 10 mM ammonium acetate buffer solution containing 0.1% formic acid–acetonitrile as mobile phase. Calibration plots were linear over the concentration range 1–500 ng mL^?1 for zofenopril and 2–1,800 ng mL^?1 for zofenoprilat. The method was successfully used to study the bioavailability of zofenopril calcium capsules relative to that of zofenopril calcium tablets in healthy Chinese volunteers.     

Determination of Five Polyphenols by HPLC/DAD and Discrimination of Apple Varieties

The objective of this study was to set up a method to detect five compounds in fresh smashed apples by HPLC/DAD simultaneously. Different methods have been tested to control browning and ascorbic acid with ultrasonication was adopted. Methanol–water–acetic acid (30:69:1, v/v) containing 2.0 g of ascorbic acid L^?1 was chosen as the extract solvent. The method effectively simplified the sample treatment compared with the traditional ways. And primarily, the results were used to identify between different varieties. The chromatographic separation was performed on an Atlantis C18 (250 mm × 4.5 mm, particle size 5 μm) with a gradient elution program using a mixture of acetonitrile and 2% aqueous acetic acid (v/v) as mobile phase within 20 min at 270 nm wavelength. The variation of the content of five compounds was gallic acid (ND ~1.81 μg g^?1), protocatechuic acid (ND ~1.79 μg g^?1), chlorogenic acid (13.81–189.4 μg g^?1), caffeic acid (6.82–45.02 μg g^?1) and rutin (0.96–18.55 μg g^?1). The results could successfully be used to discriminate between different apple varieties (Gala, Fuji, Delicious, 8th Apple US, Golden Apple, Green Apple and Red Rose); chlorogenic acid and rutin being the polyphenols that contribute most to the differentiation.     

Electrical, electrochemical, and thermomechanical properties of perovskite-type (La1?x Sr x )1?y Mn0.5Ti0.5O3?δ (x?=?0.15–0.75, y?=?0–0.05)

Strontium additions in (La_1?x Sr _x )_1?y Mn_0.5Ti_0.5O_3?δ (x?=?0.15–0.75, y?=?0–0.05) having a rhombohedrally distorted perovskite structure under oxidizing conditions lead to the unit cell volume contraction, whilst the total conductivity, thermal and chemical expansion, and steady-state oxygen permeation limited by surface exchange increase with increasing x. The oxygen partial pressure dependencies of the conductivity and Seebeck coefficient studied at 973–1223?K in the p(O₂) range from 10^?19 to 0.5?atm suggest a dominant role of electron hole hopping and relatively stable Mn³⁺ and Ti⁴⁺ states. Due to low oxygen nonstoichiometry essentially constant in oxidizing and moderately reducing environments and to strong coulombic interaction between Ti⁴⁺ cations and oxygen anions, the tracer diffusion coefficients measured by the ¹⁸O/¹⁶O isotopic exchange depth profile method with time-of-flight secondary-ion mass spectrometric analysis are lower compared to lanthanum–strontium manganites. The average thermal expansion coefficients determined by controlled-atmosphere dilatometry vary in the range 9.8–15.0?×?10^?6?K^?1 at 300–1370?K and oxygen pressures from 10^?21 to 0.21?atm. The anodic overpotentials of porous La_0.5Sr_0.5Mn_0.5Ti_0.5O_3?δ electrodes with Ce_0.8Gd_0.2O_2-δ interlayers, applied onto LaGaO₃-based solid electrolyte, are lower compared to (La_0.75Sr_0.25)_0.95Cr_0.5Mn_0.5O_3?δ when no metallic current-collecting layers are introduced. However, the polarization resistance is still high, ~2 Ω?×?cm² in humidified 10?% H₂–90?% N₂ atmosphere at 1073?K, in correlation with relatively low electronic conduction and isotopic exchange rates. The presence of H₂S traces in H₂-containing gas mixtures did not result in detectable decomposition of the perovskite phases.