Cobalt‐catalyzed Aerobic Oxidation of Eugenol to Vanillin and Vanillic Acid

A novel, simple, one‐step method of synthesizing vanillin and vanillic acid from eugenol has been developed. The method uses ligand‐ and additive‐free Co(OAc)₂ ? 4H₂O as catalyst and molecular oxygen as oxidant to achieve catalytic process without isomerizing eugenol. Extensive screening efforts were used to optimize eugenol to obtain vanillin and vanillic acid. Under optimal conditions, the reaction provided vanillin and vanillic acid with 68.5 % and 15.2 % yields, respectively. Apart from the desired products, coniferyl alcohol 9‐methyl ether and 4‐hydroxy‐3‐methoxycinnamaldehyde as two intermediates were also detected in the reaction process. Level changes of all compounds over time were presented in the reaction. The reaction pathway from eugenol to vanillic acid was validated by conducting several control experiments. Furthermore, a possible reaction mechanism dominated by a circular redox reaction from Co(III) and Co(II) species was proposed. This method offers a potentially practical alternative for manufacturing vanillin and vanillic acid efficiently.     

Determination of flavonoids,phenolic acid and polyalcohol in Butea monosperma and Hedychium coronarium by semi-preparative HPLC Photo Diode Array (PDA) Detector

The semi preparative HPLC method with PDA Detector was proposed for the determination of one phenolic acid, three flavonoids and one polyalcohol from Butea monosperma and Hedychium coronarium in gradient elution system. The influence of composition of the mobile phase concentration of the mix modifier and temperature on the separation of gallic acid, quercetin, iso-butrin, butrin and eugenol for 90 min was studied. Two different gradient programmes were used to separate these components. The lower limit of quantification of phenolic acid, flavonoids and eugenol is 0.050–0.150 μg/mL and was determined by the least square method and a good correlation was obtained for all separated components.     

New Mechanism for the Catalytic Oxidation of Lignin to Vanillin

The previously proposed mechanism for lignin oxidation to vanillin was supported experimentally. This process begins with the formation of a phenoxyl radical and ends with the step of retroaldol cleavage of substituted coniferaldehyde to vanillin. The oxidation of model compounds was studied, and experimental evidence for the proposed mechanism was obtained. The postulated intermediate coniferyl alcohol was detected in the oxidation of eugenol. The proposed mechanism was supported by kinetic data and the composition of the oxidation products of vanillideneacetone, lignosulfonates, eugenol, isoeugenol, guaiacylethanol, and guaiacylpropanol.     

Structural Studies on Inclusion Compounds of β-Cyclodextrin with Some Substituted Phenols

A detailed structural study of the inclusion compounds of some substituted phenols such as catechol, guaiacol, protocatechuic aldehyde, vanillin, caffeic acid, ferulic acid and eugenol with -cyclodextrin (CD) was carried out by using UV-visible, fluorescence, 1H and solid-state 13C NMR spectroscopic and potentiometric investigations. Based on these studies guaiacol, catechol and eugenol were found to exhibit identical orientations - with the phenyl ring within the cavity and the hydroxyl and methoxyl groups projecting outside; protocatechuic aldehyde, caffeic acid, ferulic acid and vanillin display a different orientation - with the phenol part within the cavity and the aldehyde or carboxyl part projecting outside.     

Efficient and simple method for the quantification of alkyl polyglycosides by hydrolysis and photometric determination of reducing sugars

Alkyl polyglycosides (APG) are important biodegradable surfactants for many applications. The lack of a chromophoric group and the mixture of stereoisomers and oligomers make the quantification by merely chromatic separation difficult. A simple and efficient quantification assay was developed based on the acid hydrolysis of alkyl polyglycoside and subsequent quantification of the hydrolytically cleaved glucose using the neocuproine assay. Complete hydrolysis of alkyl polyglycoside is achieved with 16 wt% sulfuric acid at 100 °C after 30  min and the separation of fatty alcohol and clouding of the reaction mixture is prevented by adding 1,2-propylene-glycol. Hydrolytically cleaved sugars reduce the Cu^(II)-neocuproine complex, leading to a color shift which permits the spectrophotometric quantification at 452 nm. A linear correlation between the absorbance of reduced Cu^(II)-neocuproine complex and glucose or alkyl polyglycoside concentration is observed up to an analyte concentration of 25 mg/L. Statistical analysis according to one-tailled T-test (S’ 95%), has shown that the lower detection limit for alkyl polyglycosides is 2.97 mg/L and the limit of quantification 8.24 mg/L, respectively. Apart from the simple execution, the assay is reliable and can be utilized both as scientific technique to quantify APG as well as for process and quality control in the industry.     

Solvent‐free method for the determination of lignin‐derived phenols in sediments

A solvent‐free method that uses headspace solid‐phase microextraction and gas chromatography with flame ionization detection is proposed for the determination of lignin‐derived phenols in sediments. The extraction and derivatization conditions for the simultaneous analysis of acetosyringone, acetovanillone, syringaldehyde, vanillin, ferulic acid, syringic acid, vanillic acid, p‐hydroxybenzoic acid, and p‐coumaric acid were optimized using a central composite design. After optimization, the best results were obtained with the following conditions: exposure of the polyacrylate fiber to the headspace with 60 μL of N ,O‐bis(trimethylsilyl)trifluoroacetamide as a derivatizing agent for 15 min and then extraction in the headspace of 100 mg of sediment (previously spiked with lignin‐derived phenols) for 35 min. The accuracy of the method was estimated based on recovery tests at two concentration levels and by comparison with a high‐performance liquid chromatography method reported in the literature. Based on the t‐test with a confidence level of 95%, no statistical differences were observed. The detection and quantification limits for the target compounds varied according to their characteristics: values at the microgram per gram level for nonacid compounds and milligram per gram level for phenolic acids, due to the lower volatility of the derivatives.     

Application of chemometric approach for development and validation of high performance liquid chromatography method for estimation of ropinirole hydrochloride

A systematic Quality by Design approach was employed for developing an isocratic reversed‐phase liquid chromatographic technique for the estimation of ropinirole hydrochloride in bulk drug and pharmaceutical formulations. LiChrospher RP 18‐5 Endcapped column (25 cm × 4.6 mm id) at ambient temperature (25 ± 2°C) was used for the chromatographic separation of the drug. The screening of factors influencing chromatographic separation of the active pharmaceutical ingredient was performed employing fractional factorial design to identify the influential factors. Optimization of the selected factors was carried out using central composite design for selecting the optimum chomatographic conditions. The mobile phase employed was constituted of Solvent A/Solvent B (65:35 v/v) (Solvent A [methanol/0.05 M ammonium acetate buffer, pH 7, 80:20 v/v] and Solvent B [high performance liquid chromatography grade water]) and used at 0.6 mL/min flow rate, while UV detection was performed at 250 nm. Linearity was achieved in the drug concentration range 5–100 µg/mL (R² = 0.9998) with limits of detection and quantification of 1.02 and 3.09 µg/mL, respectively. Method validation was performed as per ICH guidelines followed by forced degradation studies, which indicated good specificity of the developed method for detecting ropinirole hydrochloride and its possible degradation products in the bulk drug and pharmaceutical formulations.     

Analysis of caffeic acid derivatives in echinacea extracts by liquid chromatography particle beam mass spectrometry (LC–PB/MS) employing electron impact and glow discharge ionization sources

A liquid chromatography–particle beam/mass spectrometry (LC–PB/MS) method with electron impact (EI) and glow discharge (GD) ionization sources is presented for the determination of caffeic acid derivatives in echinacea tinctures. In this work, two commercially available echinacea ethanolic extracts were used as the test samples for the separation, identification, and quantification of the caffeic acid derivatives (caffeic acid, chlorogenic acid, cichoric acid, and caftaric acid), which are suggested to have beneficial medicinal properties. Detailed evaluations of the two primary controlling parameters for EI (electron energy and source block temperature) and GD (discharge current and pressure) sources were performed to determine optimal instrument operation conditions. The mass spectra obtained from both ion sources provide clear and simple molecular fragmentation patterns for each of the target analytes. The absolute detection limits for the caffeic acid derivatives were determined to be at subnanogram levels for both the EI and GD sources. The separation of the caffeic acid derivatives in echinacea was accomplished by reversed-phase chromatography using a C₁₈ column and a gradient elution system of water containing 0.1% trifluoroacetic acid and methanol, with an analysis time of less than 40 min. A standard addition method was employed for the quantification of each of the caffeic acid derivatives in the tincture.     

Cyclohexane‐1,3‐dione as a derivatizing agent for the analysis of aldehydes by micelar electrokinetic chromatography with diode array detection

Aldehydes are important compounds in a large number of samples, especially food and beverages. In this work, for the first time, cyclohexane‐1,3‐dione (CHD) was used as a derivatizing reagent aiming aldehyde (formaldehyde, acetaldehyde, propionaldehyde, and valeraldehyde) analysis by MEKC‐DAD. The optimized separation of the derivates was performed using a voltage program (+20 kV, 0–15 min.; +23 kV, 15–17 min.) at a temperature of 26°C, and using as the running buffer a mixture containing 100 mmol/L of sodium dodecyl sulfate and 29 mmol/L of sodium tetraborate at pH 9.2, with maximum absorbance at 260 nm. CHD was compared with two other derivatizing agents: 3‐methyl‐2‐benzothiazolinone hydrazone and phenylhydrazine‐4‐sulfonic acid. The CHD‐aldehyde derivatives were also characterized by LC‐MS. The calibration curves for all aldehydes had r² above 0.999 and LODs ranged from 0.01 to 0.7 mg/L. The optimized methodology was applied in sugar cane brandy (cachaça) samples successfully. CHD showed to be an alternative derivatization reagent due to its stability, aqueous solubility, high selectivity and sensitivity, reduced impurities, and simple preparation steps.     

Multi-walled carbon nanotube-based dispersive solid phase extraction with following back-extraction for HPLC/UV determination of Rosmarinic acid in lemon balm and Rosemary plant samples

In this paper, dispersive solid phase extraction with following back-extraction and HPLC/UV determination of Rosmarinic acid have been investigated. Multi-walled carbon nanotubes were used as sorbent in the suggested method. The effectiveness of some parameters such as extraction time, sorbent dosage, pH and ionic strength of the aqueous solution on Rosmarinic acid adsorption were studied. The extraction time of 5.0 min, adsorbent weight of 5.0 mg, and pH of 2.5 were obtained as the optimum experimental parameters. Adsorption of Rosmarinic acid molecules was almost independent from ionic strength. For back-extraction purpose a basic solution containing methanol was brought into contact with sorbent to desorb Rosmarinic acid molecules from sorbent containing adsorbed Rosmarinic acid molecules. Linear range of HPLC method for Rosmarinic acid quantification was 1.80–21.62 mg/L (R² = 0.998). The relative standard deviation, limit of detection, and limit of quantification for the suggested method were 0.81%, 0.68 mg/L, and 2.86 mg/L, respectively. The proposed method was applied for extraction and HPLC/UV determination of Rosmarinic acid in Lemon balm and Rosemary plant samples. Comparison between obtained chromatograms before adsorption and after desorption processes showed that suggested extraction/back-extraction process has good selectivity and efficiency for separation of Rosmarinic acid molecules from interfering molecules existing in the plant extracts. The proposed method is efficient, low cost, fast, and simple for separation, extraction, and determination of Rosmarinic acid.     

Simultaneous determination of seven phenolic acids in three Salvia species by capillary zone electrophoresis with β‐cyclodextrin as modifier

A capillary zone electrophoresis method was developed for the simultaneous determination of seven phenolic acids, including protocatechuic aldehyde ( 1 ), salvianolic acid C ( 2 ), rosmarinic acid ( 3 ), salvianolic acid A ( 4 ), danshensu ( 5 ), salvianolic acid B ( 6 ), and protocatechuic acid ( 7 ), in Danshen and related medicinal plants. A running buffer composed of 20 mM sodium tetraborate adjusted to pH 9.0, and containing 12 mM β‐cyclodextrin as modifier. Baseline separation was achieved within 17 min running at the voltage of 20 kV, temperature of 25°C and detection wavelength of 280 nm. The relative standard deviations of migration time ranged from 0.2 to 0.7% and the peak area ranged from 1.5 to 3.7% for the seven analytes, indicating the good repeatability of the proposed method. The method was extensively validated by evaluating the linearity (R² ≥ 0.9992), limits of detection (0.14–0.36 μg/mL), limits of quantification (0.47–1.19 μg/mL), and recovery (96.0–102.6%). Under the optimum conditions, samples of Danshen and related medicinal plants were analyzed using the developed method with high separation efficiency.     

Supercritical fluid chromatography coupled with tandem mass spectrometry: A high‐efficiency detection technique to quantify Taxane drugs in whole‐blood samples

We present a technique to rapid determine taxane in blood samples by supercritical fluid chromatography together with mass spectrometry. The aim of this study was to develop a supercritical fluid chromatography with mass spectrometry method for the analysis of paclitaxel, cabazitaxel, and docetaxel in whole‐blood samples of rats. Liquid‐dry matrix spot extraction was selected in sample preparation procedure. Supercritical fluid chromatography separation of paclitaxel, cabazitaxel, docetaxel, and glyburide (internal standard) was accomplished within 3 min by using the gradient mobile phase consisted of methanol as the compensation solvent and carbon dioxide at a flow rate of 1.0 mL/min. The method was validated regarding specificity, the lower limit of quantification, repeatability, and reproducibility of quantification, extraction recovery, and matrix effects. The lower limit of quantification was found to be 10 ng/mL since it exhibited acceptable precision and accuracy at the corresponding level. All interday accuracies and precisions were within the accepted criteria of ±15% of the nominal value and within ±20% at the lower limit of quantification, implying that the method was reliable and reproducible. In conclusion, this method is a promising tool to support and improve preclinical or clinical pharmacokinetic studies with the taxanes anticancer drugs.     

Decomposition Behavior of Hemicellulose and Lignin in the Step-Change Flow Rate Liquid Hot Water

Hemicellulose and lignin are the main factors limiting accessibility of hydrolytic enzymes besides the crystallinity of cellulose. The decomposition behavior of hemicellulose and lignin in the step-change flow rate hot water system was investigated. Xylan removal increased from 64.53% for batch system (solid concentration 4.25% w/v, 18?min, 184°C) to 83.78% at high flow rates of 30?ml/min for 8?min, and then 10?ml/min for 10?min. Most of them (80?C90%) were recovered as oligosaccharide. It was hypothesized that the flowing water could enhance the mass transfer to improve the sugars recovery. In addition, the solubilization mechanism of lignin in the liquid hot water was proposed according to the results of Fourier transform-infrared spectroscopy and scanning electron microscopy of the water-insoluble fraction and gas chromatography?Cmass spectrometry of the water-soluble fraction. It was proposed that lignin in the liquid hot water first migrated out of the cell wall in the form of molten bodies, and then flushed out of the reactor. A small quantity of them was further degraded into monomeric products such as vanillin, syringe aldehyde, coniferyl aldehyde, ferulic acid, and p-hydroxy-cinnamic acid. All of these observations would provide important information for the downstream processing, such as purification and concentration of sugars and the enzymatic digestion of residual solid.     

A validated method for the quantification of curcumin in plasma and brain tissue by fast narrow-bore high-performance liquid chromatography with fluorescence detection

Curcumin, a lipophilic polyphenol derived from the rhizome of the plant turmeric (Curcuma longa), might be useful in the prevention and treatment of a number of degenerative brain disorders, including glioma multiforma and Alzheimer’s disease. Thus, there is growing interest in measuring curcumin concentrations in the brain and other target tissues in relevant animal models. We therefore developed and validated (according to the Food and Drug Administration guidelines for bioanalytical method validation), a simple, fast and reliable method for the quantification of curcumin in biological matrices by fast high-performance liquid chromatography with fluorescence detection. This method involves a simple extraction with 95% ethyl acetate and 5% methanol, rapid separation (<2 min if external standards and <4 min if the internal standard β-estradiol 17-acetate is used) on a Jasco Reprosil-Pur Basic C₁₈ column (75 × 2 mm, 1.8 μm) with an eluent of acetonitrile, methanol, de-ionised water and acetic acid (49:20:30:1, v/v; flow rate, 0.4 mL/min) and fluorescence detection (excitation wavelength, 420 nm; emission wavelength, 470 nm). The method is selective, precise (<15% RSD at the lower limit of quantification), accurate (<15% of the coefficient of variation at the lower limit of quantification) and sensitive over a linear range of 0.05–10 μg/mL for curcumin. The developed method was used for the quantification of curcumin in the brains of mice force-fed (50 mg/kg bw) or i.p. injected (100 mg/kg bw) with curcumin. Brain curcumin concentrations of the mice were below the limit of detection at 30, 60 and 120 min after oral gavage and reached 4–5 μg/g brain 20–40 min after i.p. injection. In conclusion, the developed and validated method should be useful for the accurate and precise quantification of curcumin in target organs from relevant animal models of human diseases.     

Rapid analysis of tetracaine for a tape stripping pharmacokinetic study using short‐end capillary electrophoresis

A rapid and simple short‐end (reverse) capillary zone electrophoresis method was developed and validated for the separation and quantification of tetracaine in skin using tape samples. The separation was performed in a 485 mm (400 mm to window) × 50 µm internal diameter fused silica capillary using a background electrolyte of phosphoric acid–Tris pH2.5 at –25 kV. The extraction of tetracaine from tape samples was achieved using methanol diluted to 50% with water before injection. Procaine was the internal standard. The migration times for procaine and tetracaine were 1.25 and 1.36 min, respectively. The limit of quantification for tetracaine was 50 µg, with a signal‐to‐noise ratio greater than 10. The calibration curve was linear from 50 to 1200 µg with r² greater than 0.99. The CV for both within‐ and between‐assay imprecision and the percentage inaccuracy for the quality control samples including lower and upper limits of quantitation were <12.1% and <11%, respectively. The absolute mean recovery of tetracaine was >97%. The accuracy and selectivity of this method allowed the rapid measurement of tetracaine in tape samples obtained from a skin tape stripping study of local anaesthetics in healthy subjects. Copyright © 2008 John Wiley & Sons, Ltd.     

Rapid Determination of Simple Polyphenols in Grapes by LC Using a Monolithic Column

The development of a rapid, reliable and reproducible LC method for the determination and quantification of 13 polyphenols (gallic acid, protocatechuic aldehyde, gentisic acid, catechin, vanillinic acid, caffeic acid, vanillin, epicatechin, syringaldehyde, p-coumaric acid, ferulic acid, sinapic acid and resveratrol) in grapes and derived products is reported. The polyphenols were separated in less than 8 min. Employed was an RP-18e (100 mm × 4.6 mm) monolithic type column. A gradient method with the following solvents was utilised for the chromatographic separation: A: 90% water, 2% acetic acid in methanol, and B: 90% methanol, 2% acetic acid in water. Two detectors in series were employed: a UV–Vis detector and a fluorescence excitation/emission detector. Influence of temperature (15–40 °C) and solvent flow rate (2–5 mL min^?1) on the separation were studied, and 25 °C and 2.5 mL min^?1 were found to be the optimum conditions. The relative standard deviations of the resulting peak areas, for both intra- and inter- experiments, were less than 2.4 and 2.6%, respectively. Finally, the developed method has been utilised for the quantification of the polyphenols in real samples.     

Analysis of selected designer benzodiazepines by ultra high performance liquid chromatography with high‐resolution time‐of‐flight mass spectrometry and the estimation of their partition coefficients by micellar electrokinetic chromatography

A new ultra high performance liquid chromatography with electrospray ionization time of flight mass spectrometry method for the selective and sensitive separation, identification, and determination of selected designer benzodiazepines (namely, pyrazolam, phenazepam, etizolam, flubromazepam, diclazepam, deschloroetizolam, bentazepam, nimetazepam, and flubromazolam) in human serum was developed. The separation of the studied designer benzodiazepines was achieved on C₁₈ chromatographic column using gradient elution within 6 min without any significant matrix interferences. Liquid–liquid extraction with butyl acetate was applied for serum samples cleanup and preconcentration of studied designer benzodiazepines. The method was validated in terms of linearity, limit of detection, limit of quantification, matrix effects, specificity, precision, accuracy, recovery, and sample stability. The limit of detection values were 0.10–0.15 ng/mL. The method was applied to a spiked serum sample to demonstrate its applicability for systematic toxicology analysis. Furthermore, a capillary chromatographic method with micellar electrokinetic chromatography was used for the estimation of partition coefficients of studied designer benzodiazepines as important parameters to evaluate their pharmacological and toxicological properties.     

Combination of a sub‐3 μm superficially porous particle packed column with charged aerosol detection for the simple and sensitive measurement of nine macrolides in human urine

Due to the lack of chromophores in many macrolides, analytical methods based on mass spectrometry and electrochemical detection coupled to liquid chromatography have been suggested to be suitable for the quantification of macrolides in complex matrices. In this study, a simple and sensitive analytical method was established for the simultaneous measurement of nine macrolides in human urine by combining a sub‐3 μm superficially porous particle packed column with charged aerosol detection. After thorough investigation of various sample preparation methods, including two liquid–liquid extraction methods and four solid‐phase extraction methods, HLB solid‐phase extraction was selected and further optimized. Absolute recovery of the optimized sample preparation method ranged from 99.5–110.2%, indicating its very high extraction/clean‐up efficiency. For chromatography, parameters influencing macrolide separation were systematically optimized, and the resulting conditions allowed baseline separation of nine macrolides within 24 min using a very simple mobile phase. The established method was validated for linearity, limit of detection, limit of quantification, absolute recovery, and precision. Based on its limit of detection (0.025–0.100 μg/mL), the method had similar or greater sensitivity than most methods based on electrochemical detection. It was found that the current method was appropriate for application to real human urine samples after drug administration.     

Sensitive determination of biogenic amines by capillary electrophoresis with a new fluorogenic reagent 3-(4-fluorobenzoyl)-2-quinolinecarboxaldehyde

An effective approach was proposed to the derivatization of seven biogenic amines using 3-(4-fluorobenzoyl)-2-quinolinecarboxaldehyde (FBQCA) as a fluorogenic reagent. The sensitive determinations of these derivatives were achieved by micellar electrokinetic capillary chromatography (MEKC) with laser-induced fluorescence (LIF) detection. The derivatization and electrophoretic conditions have been optimized. A running buffer was composed of mixtures of 25 mM pH 9.5 boric acid, 25 mM SDS, and 27% ACN. At 25 °C and 22.5 kV, the baseline separation of the derivatives was accomplished in 13 min. The detection limit (S/N = 3) was found as low as 0.4 nM. The proposed method was validated by the linearity of two orders magnitude and correlation coefficient in the range 0.9969–0.9998. Also, the procedure was successfully applied to the determination of biogenic amines in soy sauce, fish and wine samples.     

Development,validation and application of a UHPLC–MS/MS method for quantification of the adiponectin-derived active peptide ADP355 in rat plasma

A UHPLC–MS/MS method for the quantification of ADP355, an adiponectin-derived active peptide, was developed and validated. The extraction method employed simple protein precipitation using methanol and chromatographic separation was achieved on anAccucore™ RP-MS C₁₈ column (100 × 2.1 mm, 2.6 μm, 80 Å), using 0.1% formic acid in both water and acetonitrile with gradient elution at the flow rate of 400 μl/min within 4.0 min. Detections were performed under positive ion mode with multiple reaction monitoring ion transitions m/z 1109.2 → 309.8 and 871.4 → 310.1 for ADP355 and Jt003 respectively at unit resolution. The linearity range of the calibration curve was 2–1,000 ng/ml with a lower limit detection of 0.5 ng/ml. The selectivity, linearity, precision, accuracy, recovery, matrix effect and stability were validated, and all items met the requirement of US Food and Drug Administration guidance. This method was successfully applied to an intravenous pharmacokinetic study of ADP355 in rats and the in-vitro stability in rat serum, plasma and whole blood was also assessed.