Quantitative determination of (-)-epicatechin in cider apple juices by (1)H NMR

This paper reports a quantitative determination method of (−)-epicatechin in apple juices by measuring of its signal at 7.05 ppm in the ¹H NMR spectrum. It is a direct method that does not need any previous derivatization. 1,3,5-Benzenetricarboxylic acid was added to the juice as internal standard for the determination of the absolute concentration of (−)-epicatechin. Ascorbic acid was also added to avoid enzymatic oxidation of the phenolics and to adjust the pH at 2.74, since the chemical shift of some compounds varies with the pH. Standard addition method accomplished with the juices of two different varieties of apples gave recoveries between 95 and 109%. The precision of the method was tested for repeatability (n=5) and reproducibility (n=13) obtaining a coefficient of variation of 5.8 and 8.6%, respectively. Limit of detection, calculated from “3S_y/x+intercept”, is 24 mg l⁻¹.     

High-performance liquid chromatographic determination of furfural and hydroxymethylfurfural in apple juices and concentrates

Summary A rapid and sensitive method for determining 2-furaldehyde (FUR) and 5-hydroxymethyl-2-furaldehyde (HMF) in apple juices and juice concentrates has been developed. The method for FUR and HMF involves the solid-liquid extraction of the juice by using a C-18 cartridge prior to reversed-phase separation with detection at 280 nm. The mobile phase was acetonitrile-water (8/92, v/v) at a flow rate of 1.0 ml/min. Recoveries from apple juices and juice concentrates spiked at different levels ranged from 94.1 to 104.0 (FUR) and 94.5 to 100.5 (HMF). The quantification limit for both, FUR and HMF, was 5 ppb.     

High-performance liquid chromatographic determination of major organic acids in apple juices and ciders

Summary A reversed-phase high-pressure liquid chromatographic method is presented for the simultaneous separation and determination of malic, citric, lactic, succinic and ascorbic acids in apple juices and ciders. After filtration and/or degasification, the organic acids in the sample are separated on a LiChrosorb/C₁₈ column and quantified by using a rapid diode array detector. The method is considered to be a suitable choice for the accurate and precise determination (C.V. 5%) of these compounds.     

Optimization of clean-up procedure for patulin determination in apple juice and apple purees by liquid chromatography

Patulin (PAT) is a mycotoxin produced in fruits, mainly in apples, by several fungal species that can be carried into industrial apple juice by-products during factory processing. An analytical method for determination of PAT in apple juice and another one for determination of this compound in apple purees and apple compotes by liquid chromatography are proposed in the present paper. These methods have better precision and sensitivity than previously reported methods and focus mainly on extraction and clean-up. To accomplish analytical methods with higher accuracy, lower limits of detection and simpler procedures for application in quality control of the goods, different extraction and clean-up procedures for PAT were comparatively studied. PAT recoveries in apple juice spiked with 1.0 mg PAT/kg varied between 52.3% and 81.0%. The highest PAT recovery in apple puree spiked with 0.1 mg PAT/kg was 82.9%. Addition of NaH₂PO₄ during the extraction phase here reported for the first time has the advantage of keeping the pH slightly acidic, thus avoiding PAT degradation.     

Comparison of sample preparation methods for the ICP-AES determination of minor and major elements in clarified apple juices

Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of minor and major elements present in apple juices. Prior to ICP-AES measurement, samples were diluted with nitric acid or digested in a microwave assisted digestion system. The differences in the measured element concentrations after application of different types of sample preparation procedures are discussed. The direct measurement compared to closed microwave dissolution was found to be the best sample preparation procedure. Prior to the measurements the ICP-AES method was validated and optimized for the determination of elements in apple juices. For diluted apple juice samples the lowest limits of detection (LOD) were obtained for Ba and Cd (< 20 μg L^{− 1}), moderate ones for Cu, Mn, Ni, Fe, Ag, Ca, Cr, Zn, Mg, and Sr (20–100 μg L^{− 1}), and the highest LODs for K, Pb, Na, and Al (> 110 μg L^{− 1}). The results obtained for the repeatability (< 0.9%), the intermediate precision (< 4.5%), the day-to-day reproducibility (< 5.2%), and the overall uncertainty of measurement (approx. 4–7%) for all elements analyzed demonstrated the good applicability of the proposed method. Differences in major element content in fresh and commercial apple juice are discussed.     

Rapid reversed-phase liquid chromatographic determination of patulin in apple juice

A rapid, simple and economical method using a limited amount of organic solvent is described for the determination of patulin in apple juice. The sample was extracted with ethyl acetate and the extract was cleaned up by extraction with sodium carbonate solution. Patulin was then determined by reversed-phase liquid chromatography using a MicroPak C₁₈ column and a variable-wavelength UV-Vis detector set at 276 nm. Patulin and 5-hydroxymethylfurfural were completely resolved by using water- acetonitrile (99:1, v/v) as the mobile phase at a flow-rate of 1.0 ml/min. The detection limit was <5 μg/1 and the recovery was 98%.     

Direct determination of mercury in cosmetic samples by isotope dilution inductively coupled plasma mass spectrometry after dissolution with formic acid

A new method was proposed for the accurate determination of mercury in cosmetic samples based on isotopic dilution (ID)-photochemical vapor generation (PVG)-inductively coupled plasma mass spectrometry (ICP MS) measurement. Cosmetic samples were directly dissolved in formic acid solution and subsequently subjected to PVG for the reduction of mercury into vapor species following by ICP MS detection. Therefore, the risks of analyte contamination and loss were avoided. Highly enriched ²⁰¹Hg isotopic spike is added to cosmetics and the isotope ratios of ²⁰¹Hg/²⁰²Hg were measured for the quantitation of mercury. With ID calibration, the influences originating from sample matrixes for the determination of mercury in cosmetic samples have been efficiently eliminated. The effects of several experimental parameters, such as the concentration of the formic acid, and the flow rates of carrier gas and sample were investigated. The method provided good reproducibility and the detection limits were found to be 0.6 pg mL⁻¹. Finally, the developed method was successfully applied for the determination of mercury in six cosmetic samples and a spike test was performed to verify the accuracy of the method.     

离子排斥色谱法测定甘油催化氧化产物中的H2CO3和HCOOH

建立了测定甘油催化氧化产物中H2CO3和HCOOH的离子排斥色谱分析方法。采用离子排斥柱分离,分别用纯水和4 mmol/L HCl作流动相进行H2CO3和HCOOH的分析。检测方式为非抑制电导检测。实验结果显示,H2CO3和HCOOH工作曲线的线性范围为2～100 mg/L和6.23～124.6 mg/L,检出限分别为0.45 mg/L和2.49 mg/L(S/N=3)。H2CO3的保留时间和峰面积的相对标准偏差分别为0.07%和4.0%,HCOOH的保留时间和峰面积的相对标准偏差分别为0.09%和2.2%。方法已用于甘油催化氧化产物中H2CO3和HCOOH的分析。     

Analysis of formic and acetic acid in rain water by capillary electrophoresis

A simple technique is described for the routine capillary electrophoretic determination of formic and acetic acid in rain water. These acids were determined simultaneously in approximately 6 min using a carrier electrolyte containing lO mM phosphate and 0.5 mM myristyltrimethylammonium bromide (MTAB) as electroosmotic flow (EOF) modifier at pH 6.5 and direct UV detection at 185nm. The method is quantitative, with recoveries in the 99-101% range and linear up to 5mgL^-1. The precision is better than 2.1% and the procedure shows the appropriate sensitivity, with detection limits between 0.042 and 0.055mg L^-1. The proposed method was successfully employed for the determination of formic and acetic acid in 57 rain water samples, collected from October 2000 to February 2001 in four different sampling stations located in Galicia (NW Spain), by direct sample injection after filtration.     

Determination of trace elements in biological samples treated with formic acid by inductively coupled plasma mass spectrometry using a microconcentric nebulizer

A simple and fast method for the determination of As, Ba, Cd, Co, Cu, Fe, Ga, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, U, V and Zn in biological samples by inductively coupled plasma mass spectrometry (ICP-MS), after sample solubilization with formic acid and introduction by a microconcentric nebulizer, is proposed. The sample is mixed with formic acid, kept at 90 °C for one hour and then diluted with nitric acid aqueous solution to a 50% v/v formic acid and 1% v/v nitric acid final concentrations. The final sample solution flow rate for introduction into the plasma was 30 μL min⁻¹. The optimized and adopted nebulizer gas flow rate was 0.7 L min⁻¹ and RF power was 800 W. These conditions are very different than those normally used when a conventional nebulizer is employed. Rodhium was used as internal standard. External calibration against aqueous standard solutions, without formic acid, could be used for quantification, except for As, Se and Zn. However, external calibration with 50% formic acid allows the determination of all analytes with high accuracy and it is recommended. The detection limits were between 0.0005 (Tl) and 0.22 mg kg⁻¹ (Fe) and the precision expressed by the relative standard deviations (RSD) were between 0.2% (Sr) and 3.5% (Ga). Accuracy was validated by the analysis of four certified reference biological materials of animal tissues, comparing the results by linear regressions and by the t-test at a 95% confidence level. The recommended procedure avoids plasma instability and carbon deposit on the cones.     

Mass spectrometry and NMR analysis of ligand binding by human liver fatty acid binding protein

Human liver fatty acid binding protein (hL‐FABP) is the most abundant cytosolic protein in the liver. This protein plays important roles associated to partitioning of fatty acids (FAs) to specific metabolic pathways, nuclear signaling and protection against oxidative damage. The protein displays promiscuous binding properties and can bind two internal ligands, unlike FABPs from other tissues. Different topologies for the ligand located in the more accessible site have been reported, with either a ‘head‐in’ or ‘head‐out’ orientation of the carboxylate end. Electrospray‐ionization mass spectrometry and nuclear magnetic resonance titrations are employed here in order to investigate in further detail the binding properties of this system, the equilibria established in solution and the pH dependence of the complexes. The results are consistent with two binding sites with different affinity and a unique head‐out topology for the second molecule of either ligand. Competition experiments indicate a higher affinity for oleic acid relative to palmitic acid at each binding site. Copyright © 2013 John Wiley & Sons, Ltd.     

Mesoporous silica-supported V-substituted heteropoly acid for efficient selective conversion of glycerol to formic acid

V-substituted polymolybdenum phosphoric acid (PV_xMo) supported on mesoporous silica was prepared and investigated as a catalyst for the oxidation of glycerol to formic acid in a batch operation. Different synthetic methods for PV_xMo supported on mesoporous silica were compared. Detailed characterizations of the final products were carried out by N₂ adsorption and desorption, XRD, HR-TEM, SEM, ICP-OES, XANES, NH₃-TPD, and FTIR to identify the chemical properties and the porous structure of silica-supported PV_xMo, as well as the strong interactions between PV_xMo with the silica skeleton. These critical properties explain the bifunctionality of silica-supported PV_xMo as a catalyst for the selective oxidation of glycerol to formic acid with standing stability.     

Highly active and stable porous polymer heterogenous catalysts for decomposition of formic acid to produce H2

Formic acid (FA) has attracted extensive attention as a hydrogen storage material. Here, we develop two heterogeneous catalysts based on porous organic polymers (POPs). After loading the Ru species, the catalyst bearing the triphenylphosphine ligand showed excellent performance in terms of activity and stability for the decomposition of FA to produce hydrogen.     

Simultaneous determination of formic acid and lower carbonyls in air samples by DNPH derivatization

The classical derivatization method of carbonyls based on 2,4-dinitrophenylhydrazine (DNPH)-coated silica cartridges was tested to concurrently measure lower carbonyls and carboxylic acids in air samples. The performance of these cartridges with respect to formic and acetic acids was evaluated in a number of laboratory measurements on collection and reaction efficiencies. The results showed that HCOOH appeared to have been efficiently collected and derivatized (at 80 degrees C for 8 h) up to air-flow rates of 350 mL/min, while CH(3)COOH was almost completely lost from the cartridge above 100 mL/min. Also due to the high LOD of HCOOH (0.8 microg/m(3)) for 120 L of air sampled during 8 h, the DNPH method might be used only in indoor environments polluted by formic acid as well as carbonyls.     

群多普利溶液构象的NMR研究

采用1D和2D NMR技术对血管紧张素转化酶抑制剂群多普利在CDCl₃溶液中存在的两种构象进行了结构解析, 并结合分子动力学和密度泛函理论方法对其进行了结构的几何优化和能量计算. 结果表明, 群多普利因分子中酰胺键的旋转而形成反式构象A和顺式构象B, 两种构象的能量差为6.35 kJ/mol, 且顺式构象为该药物的优势构象.     

Low temperature design of titanium dioxide anatase materials decorated with cyanuric acid for formic acid photodegradation

The influence of cyanuric acid (CA) on the structural, textural, electronic, morphological properties and the photocatalytic activity of titanium dioxide materials (TNCA) were herein evaluated. TNCAs samples were prepared through the sol gel method. The novelty of this work that cyanuric acid; the so far most recalcitrant molecule, is used here as reservoir of nitrogen. The synthesis of TNCAs nanomaterials are performed at low temperature in presence of quaternary ammonium as co-catalyst for anatase growth. Samples were characterized by means of nitrogen adsorption-desorption isotherms at 77 K, X-ray diffraction (XRD), Infrared (ATR), Raman, diffuse reflectance ultraviolet-visible, photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic activities of TNCAs and their free counterpart nanomaterials were then evaluated in the photocatalytic degradation of formic acid (FA) as model molecule under UV.X-ray and Raman show success of anatase phase formation at low temperature without any post-calcination. IR-ATR analysis confirms CA grafting onto TiO₂ identified by formation of vibration band between Ti and triazine. SEM mapping shows that C, O, Ti, and N are homogeneously distributed in the nanomaterial. Nitrogen adsorption-desorption measurements at 77 K show developed textural properties; the heat of N₂ adsorption seems to be affected by CA loading. PL and UV-visible spectroscopies show simultaneously (i) electron trapping by the oxygen vacancy identified by Raman spectroscopy by redshift of Eg1 mode and (ii) the hole is confined by nitrogen. Therefore, the excited electron can move from TiO₂ VB to the new sublevels initiated by the introduction of nitrogen which results in quenching of the photoluminescence intensity. The photocatalytic activity of the various TNCAs nanomaterials increases versus CA loading. The highest k_LH of TNCA2 (5 wt%) could be explained by short migration time conjugated with lower bulk recombination of the photogenerated electron hole.     

Investigation of tetracaine complexation with beta-cyclodextrins and p-sulphonic acid calix[6]arenes by nOe and PGSE NMR

Cyclodextrins (CD) and calixarenes are complexing agents that have been successfully used as pharmaceutical drug carriers, to improve the bioavailability of medicines. The aim of this work was to investigate the complexation of the local anesthetic tetracaine 1 with β-cyclodextrin 2, as well as with p-sulphonic acid calix[6]arene 3. ¹H NMR experiments were carried out in D₂O, i.e., with the charged tetracaine species 1. HR-DOSY ¹H NMR allowed determination of the fraction of complexed population (%p _bound = 55% and 70%) and the apparent association constants (K _a = 1358 and 3889 M⁻¹), respectively, for 1/2 and 1/3. These results confirm that a strong association takes place between 1 and 2, while the 1/3 complex is even more stable, due to the negatively charged sulphonic groups of 3. Studies conducted at pH 10 revealed that the association of the uncharged form of 1 with 3 is considerably weaker, while that with 2 increased significantly (K _a = 6597 M⁻¹), protecting the anesthetic against alkaline hydrolysis. ¹H-ROESY 1D NMR experiments allowed determination of the host-guest relative positions, revealing that the proposed topologies for the 1/2 and 1/3 complexes were quite different. The complexation of 1 with either 2 or 3 is being investigated in view of its potential use in new therapeutic formulations, designed to increase the bioavailability and/or to decrease the systemic toxicity of tetracaine, in anesthesia procedures.     

特丁基二甲基硅烷衍生化气相色谱-质谱联用法快速测定苹果汁中的棒曲霉素

运用特丁基二甲基硅烷(TBDMS)衍生化气相色谱-质谱(GC-MS)联用法快速、高灵敏地测定了苹果汁中的棒曲霉素(PAT)。样品用乙酸乙酯-正己烷提取,Carb/C18混合型固相萃取柱净化,TBDMS衍生,GC-MS测定,选择离子监测(SIM)模式,外标法定量。在0.01～1 mg/L的范围内线性良好(r＞0.98),在2～50 μg/kg的添加水平范围内,平均回收率为88%～98%,相对标准偏差(RSD)为5.3%～13.6%, PAT的检出限为0.5 μg/kg,测定低限为2 μg/kg。该方法快速、高灵敏、准确、专一、耐用,适合对苹果汁中PAT进行确证和定量测定。     

The use of electrothermal vaporizer coupled to the inductively coupled plasma mass spectrometry for the determination of arsenic,selenium and transition metals in biological samples treated with formic acid

A fast method for the determination of As, Co, Cu, Fe, Mn, Ni, Se and V in biological samples by ETV-ICP-MS, after a simple sample treatment with formic acid, is proposed. Approximately 75 mg of each sample is mixed with 5 mL of formic acid, kept at 90 °C for 1 h and then diluted with nitric acid aqueous solution to a 5% (v/v) formic acid and 1% (v/v) nitric acid final concentrations. A palladium solution was used as a chemical modifier. The instrumental conditions, such as carrier gas flow rate, RF power, pyrolysis and vaporization temperatures and argon internal flow rate during vaporization were optimized. The formic acid causes a slight decrease of the analytes signal intensities, but does not increase the signal of the mainly polyatomic ions (¹⁴N³⁵Cl⁺, ¹⁴N¹²C⁺, ⁴⁰Ar¹²C⁺, ¹³C³⁷Cl⁺, ⁴⁰Ar³⁶Ar⁺, ⁴⁰Ar³⁵Cl⁺, ³⁵Cl¹⁶O⁺, ⁴⁰Ar¹⁸O⁺) that affect the analytes signals. The effect of charge transfer reactions, that could increase the ionization efficiency of some elements with high ionization potentials was not observed due to the elimination of most of the organic compounds during the pyrolysis step. External calibration with aqueous standard solutions containing 5% (v/v) formic acid allows the simultaneous determination of all analytes with high accuracy. The detection limits in the samples were between 0.01 (Co) and 850 μg kg⁻¹ (Fe and Se) and the precision expressed by the relative standard deviations (RSD) were between 0.1% (Mn) and 10% (Ni). Accuracy was validated by the analysis of four certified reference biological materials of animal tissues (lobster hepatopancreas, dogfish muscle, oyster tissue and bovine liver). The recommended procedure avoids plasma instability, carbon deposit on the cones and does not require sample digestion.