Infrared spectra of p-, m- and o-fluorobenzaldehyde in low temperature argon matrices

Three structural isomers of fluorobenzaldehyde (p-, m- and o-forms) have been investigated in detail with matrix-isolation infrared spectroscopy, in the 700-3000 cm⁻¹ region, combined with the UV photoexcitation and the density functional calculations. Two rotamers (syn and anti) were identified for m- and o-fluorobenzaldehyde upon the photoexcitation and most of the bands of each rotamer were assigned. It is shown that the formation of the intramolecular C-H?F hydrogen bond for the anti rotamer of o-FB results in the shortening of the aldehyde C-H bond length and that the C-F and/or CO bond lengths are shortened for the syn rotamer of o-FB presumably due to the repulsion between the aldehyde O and F atoms.     

Validation of an online dual-loop cleanup device with an electrospray ionization tandem mass spectrometry-based system for simultaneous quantitative analysis of urinary benzene exposure biomarkers trans, trans-muconic acid and S-phenylmercapturic acid

The aim of this study is to validate isotope-dilution electrospray ionization tandem mass spectrometry (ESI-MS-MS) method with a dual-loop cleanup device for simultaneous quantitation of two benzene metabolites, trans, trans-muconic acid (ttMA) and S-phenylmercapturic acid (SPMA), in human urine. In this study, a pooled blank urine matrix from rural residents was adopted for validation of the analytical method. The calibration curve, detection limit, recovery, precision, accuracy and the stability of sample storage for the system have been characterized. Calibration plots of ttMA and SPMA standards spiked into two kinds of urine matrixes over a wide concentration range, 1/32-8-fold biological exposure indices (BEIs) values, showed good linearity (R > 0.9992). The detection limits in pooled urine matrix for ttMA and SPMA were 1.27 and 0.042 μg g⁻¹ creatinine, respectively. For both of ttMA and SPMA, the intra- and inter-day precision values were considered acceptable well below 25% at the various spiked concentrations. The intra- and inter-day apparent recovery values were also considered acceptable (apparent recovery >90%). The ttMA accuracy was estimated by urinary standard reference material (SRM). The accuracy reported in terms of relative error (RE) was 5.0 ± 2.0% (n = 3). The stability of sample storage at 4 or −20 °C were assessed. Urinary ttMA and SPMA were found to be stable for at least 8 weeks when stored at 4 or −20 °C. In addition, urine samples from different benzene exposure groups were collected and measured in this system. Without tedious manual sample preparation procedure, the analytical system was able to quantify simultaneously ttMA and SPMA in less than 20 min.     

Determination of methanol in o,o-dimethyldithiophosphoric acid (DMDTPA) of technical grade by UV/vis spectrophotometry and by HPLC

Two procedures are proposed in this work for the determination of methanol impurities in o,o-dimethyldithiophosphoric acid (DMDTPA). To avoid possible interferences from the main component, DMDTPA was precipitated in the form of insoluble lead complex. Free Pb(II) ions were eliminated with sulfuric acid and methanol was oxidized to formaldehyde with potassium permanganate in methanesulfonic acid medium. Finally, the excess of oxidizing agent was neutralized with saturated sodium oxalate. The above pretreatment procedure was identical for spectrophotometric assay and for chromatographic determination. In the first case, the solution obtained was treated with Nash reagent to form 3,5-diacetyl-1,4-dihydrolutidine (λ_max = 415 nm). In the calibration range 0.1-1.0% (methanol in DMDTPA), the analytical figures of merit were: R² = 0.9993, quantification limit 0.02% methanol in DMDTPA coefficient of variance (n = 5) for 0.1% and 0.4% methanol respectively 6.7% and 2.4%. Recoveries obtained in the sample fortified with 0.1, 0.2, 0.4% of methanol (in DMDTPA) were in the range 99-105%. For chromatographic procedure, formaldehyde was derivatized with 2,4-dinitrophenylhydrazine and separation was achieved on Luna C18(2) column using the isocratic elution with acetonitrile-water (70:30, v/v) and spectrophotometric detection at 360 nm. In the calibration range 0.05-0.25% (methanol in DMDTPA), R² was always higher than 0.999, the quantification limit was 0.004% and the recoveries in these same fortified samples in the range 98-101%. No statistically significant differences were observed between the results obtained in the analysis of technical grade DMDTPA by the two procedures (ANOVA, p < 0.05)     

Cyclophosphazenes tethered together via N-ring centres with ortho-, meta- and para-xylylene linkers

Hexakis (organoamino) cyclotriphosphazenes (RNH)₆P₃N₃ {R = i-Bu (1), R = i-Pr (2)} react with ortho-, meta- and para-derivatives of α,α′-dibromo xylene in 2:1 ratio to form salts of compositions [{(RNH)₆P₃N₃}₂xyl]Br₂, {R = i-Bu, o-xyl (3); R = i-Pr, m-xyl (4); R = i-Pr, p-xyl (5)}. These contain dications consisting of two phosphazene rings, which are tethered together via ring N centres by a xylylene unit. X-ray structure analyses show that the substitution pattern at the xylylene bridge controls the orientation and distance between the two tethered phosphazene rings. The solid state structures exhibit dense networks of hydrogen bonds linking dications and anions. Direct N-H?N bonds between dications are observed in the crystal structure of 3.     

Carbon nanotube field-effect transistor detector associated to gas chromatography for speciation of benzene,toluene, ethylbenzene, (o-, m- and p-)xylene

An analytical methodology based on a field-effect transistor detector using carbon nanotubes (NTFET) coupled to a gas chromatograph has been developed for the speciation of the following aromatic compounds: benzene, toluene, ethylbenzene, m-xylene, p-xylene and o-xylene (BTEX). This methodology combines the proven separation capability of gas chromatography (GC) with the potential for detection of a NTFET. The developed analyzer shows a high and stable analytical response upon repeated analysis of BTEX during 4 weeks, with detection limit less than 4 μg/L. The GC–NTFET system also shows a great suitability for actual monitoring of indoor atmospheres and no significant difference was observed between the results obtained by the developed analyzer and a more classical analytical methodology, namely gas chromatography–flame ionization detection (GC–FID).     

Nanogold-actuated biomimetic peroxidase for sensitized electrochemical immunoassay of carcinoembryonic antigen in human serum

We present a method for the simultaneous determination of guanidinosuccinic acid (GSA) and guanidinoacetic acid (GAA) from urine by protein precipitation and liquid chromatography/tandem mass spectrometry. The chromatographic separation was performed using a cation exchange column with an elution gradient of 0.1 mM and 20 mM ammonium acetate buffers. GSA was detected with the mass spectrometer in negative ion mode monitoring at m/z 174.1, and GAA, creatinine, arginine, and homoarginine were in positive ion mode monitoring at m/z 118.1, 114.1, 175.1, and 189.1, respectively. As an internal standard, l-arginine-¹³C₆ hydrochloride and creatinine-d₃ (methyl-d₃) were used. The calibration ranges were 0.50-25.0 μg mL⁻¹, and good linearities were obtained for all compounds (r > 0.999). The intra- and inter-assay accuracies (expressed as recoveries) and precisions at three concentration levels (1.00, 5.00 and 25.0 μg mL⁻¹) were better than 83.8% and 7.41%, respectively. The analytical performance of the method was evaluated by determination of the compounds in urine from male C57BL/J Iar db/db diabetes mellitus (DM) mice. The values of GSA and GAA corrected by the ratios of the individual compounds to creatinine were significantly increased in DM mice compared with control mice. These results indicated that the newly developed method was useful for determining urinary guanidino compounds and metabolites of arginine.     

Simultaneous detection of ascorbate and uric acid using a selectively catalytic surface

The direct and selective detection of ascorbate at conventional carbon or metal electrodes is difficult due to its large overpotential and fouling by oxidation products. Electrode modification by electrochemical reduction of diazonium salts of different aryl derivatives is useful for catalytic, analytical and biotechnological applications. A monolayer of o-aminophenol (o-AP) was grafted on a glassy carbon electrode (GCE) via the electrochemical reduction of its in situ prepared diazonium salts in aqueous solution. The o-aminophenol confined surface was characterized by cyclic voltammetry. The grafted film demonstrated an excellent electrocatalytic activity towards the oxidation of ascorbate in phosphate buffer of pH 7.0 shifting the overpotential from +462 to +263 mV versus Ag/AgCl. Cyclic voltammetry and d.c. amperometric measurements were carried out for the quantitative determination of ascorbate and uric acid. The catalytic oxidation peak current was linearly dependent on the ascorbate concentration and a linear calibration curve was obtained using d.c. amperometry in the range of 2-20 μM of ascorbate with a correlation coefficient 0.9998, and limit of detection 0.3 μM. The effect of H₂O₂ on the electrocatalytic oxidation of ascorbate at o-aminophenol modified GC electrode has been studied, the half-life time and rate constant was estimated as 270 s, and 2.57 × 10⁻³ s⁻¹, respectively. The catalytically selective electrode was applied to the simultaneous detection of ascorbate and uric acid, and used for their determination in real urine samples. This o-AP/GCE showed high stability with time, and was used as a simple and precise amperometric sensor for the selective determination of ascorbate.     

Fluorimetric determination of phytic acid in urine based on replacement reaction

A sensitive fluorimetric method for determination of phytic acid in human urine samples was described. The method was based on a fluorimetric replacement reaction, in which the added phytic acid replaced the Cu²⁺ ion from Cu²⁺-gelatin complex, liberating the fluorescent gelatin molecule. The fluorescence of the solution was accordingly recovered proportionally to the amount of the foreign phytic acid. The excitation wavelength was 273.5 nm and the characteristic emission wavelength was 305.0 nm, respectively. The calibration graph was obtained by plotting the recovered fluorescent intensity at maximum 305.0 nm against the added standard phytic acid, and was divided into two sections. One section was linear over the range of 0.40-2.40 mg L⁻¹ with a linear regression equation of I_f = −0.895 + 15.146c (R² > 0.9993), and the other over the range of 2.40-9.20 mg L⁻¹ with a linear regression equation of I_f = −29.526 + 26.113c (R² > 0.9996), respectively. The relative standard deviation (R.S.D.) at 95% confidence degree for a 2.0 mg L⁻¹ of standard phytic acid within 1 month was less than 1.26% (n = 5), indicating the procedure is reproducible. The detection and the quantification limits of phytic acid were estimated to be 0.23 and 0.40 mg L⁻¹, respectively. The proposed method was applied to the determination of phytic acid in urine samples and the found concentrations of phytic acid in urine were in the range of 0.49-0.75 mg L⁻¹ with recoveries of 96.2-108.8%. Comparison of the obtained results with the reported HPLC was performed, indicating the proposed method was reliable.     

Metabolism profile of scutellarin in urine following oral administration to rats by ultra performance liquid chromatography coupled to time-of-flight mass spectrometry

Scutellarin, a flavone glucuronide of 5,6,4′-trihydroxyflavone-7-O-glucoronide, is the main active component of the traditional Chinese botanic drug Erigeron breviscapus (Vant.) Hand.-Mazz. In this study, a method based on ultra performance liquid chromatography coupled with a time-of-flight mass spectrometer (UPLC/TOF MS) was established and validated to profile the metabolites of scutellarin in Sprague-Dawley rat urine following oral administration of single dose of scutellarin at 80.8 mg/kg. The column utilized was an Acquity BEH C18 (150 mm × 2.1 mm, 1.7 μm). The mobile phase was 0.2% formic acid and acetonitrile with gradient condition. Two standard curves of scutellarin were obtained for the concentration range of 1.065-10.65 μg/mL and 10.65-63.92 μg/mL, respectively. By automating the data processing of the software Masslynx developed by Waters Ltd., 17 metabolites of scutellarin were found and determined in rat urine, with the corresponding reactions in vivo such as isomerism, reduction, methylation, glucuronide conjugation, hydroxylation, hydroxylation and methylation, etc., most of which were discovered for the first time. For most metabolites, the time (T_p) of peak excretion was 8-12 h. Calculated as scutellarin, the cumulative urine excretion rate of the metabolites was 1.93%.     

A solid-phase extraction and size-exclusion liquid chromatographic method for polyethylene glycol 25 p-aminobenzoic acid determination in urine: validation for urinary excretion studies of users of sunscreens

No previous publications about percutaneous absorption of polyethylene glycol 25 p-aminobenzoic acid (PEG-25 PABA) have been found in the literature and the expected levels to be found in human urine after sunscreens use are unknown. The method proposed here is suitable to determine PEG-25 PABA in the urine of sunscreens users in order to carry out studies on body accumulation/excretion. It is based on solid-phase extraction (SPE) with size-exclusion liquid chromatography determination. Solid-phase extraction allows the analyte to be retained and subsequently eluted for a clean-up, using a silica-based cartridge. The size-exclusion liquid chromatography of the eluted allows the rest of matrix interferences to be avoided. Fluorescence intensity was measured at λ_em = 350 nm (λ_exc = 300 nm). The sensitivity of the proposed method is in the order of 450 ± 5 mL ng⁻¹ and the detection limit (3 S_y/x/b) in the measured solutions is in the order of 13 ng mL⁻¹, that is 2.6 ng mL⁻¹ in urine samples. The method enables PEG-25 PABA to be determined in both, spiked and unspiked human urine samples. Results obtained for spiked human urine samples (11-100 ng mL⁻¹) demonstrated the accuracy of the method. The mean relative standard deviation of the results was in the order of 3-10%. Three volunteers applied a sunscreen lotion containing a 8% PEG-25 PABA sunscreen cream and their urinary excretion was controlled from the moment of application until the excreted amounts were no longer detectable.     

A cationic mononuclear and a neutral trinuclear boron compound derived from boric acid and N2O2-type ligands of the Salan class

Four different ligands of the Salan class have been prepared and reacted with boric acid. Reaction of saleanH₄ (saleanH₄ = N,N′-bis(o-hydroxybenzyl)-1,2-diaminoethane) with three equivalents of boric acid gave a neutral trinuclear boron complex containing two four-coordinate and one three-coordinate boron atom involved in a system of four heterocyclic rings of the composition {C₃BNO}, {C₂B₂N₂O} and {B₃O₃}. The salceanH₄ ligand (salceanH₄ = N,N′-bis(o-hydroxybenzyl)-trans-1,2-diaminocyclohexane) gave a so far unknown mononuclear boronium complex of the general formula [(RO)₂B(NR′R′′)₂]⁺. Both compounds might have applications, the trinuclear species as Lewis acid catalyst and the borocation as positively charged counterion for voluminous anions. With salpanH₄ (salpanH₄ = N,N′-bis(o-hydroxybenzyl)-1,3-diaminopropane) and salophanH₄ (salophanH₄ = N,N′-bis(o-hydroxybenzyl)-1,2-diaminobenzene) only unseparable product mixtures of oligo- and/or polymeric boron complexes could be obtained.     

Calorimetric determination of enthalpy changes for proton ionization of N-[2-hydroxyethyl]piperazine-N′-[2-ethane sulfonic acid] (HEPES) and N-[2-hydroxyethyl]piperazine-N′-[2-hydroxypropane sulfonic acid] (HEPPSO) in water-methanol mixtures

Enthalpies for the two proton ionizations of the biochemical buffers N-[2-hydroxyethyl]piperazine-N′-[2-ethane sulfonic acid] (HEPES) and N-[2-hydroxyethyl]piperazine-N′-[2-hydroxypropane sulfonic acid] (HEPPSO) were obtained in water-methanol mixtures with methanol mole fraction (X_m) from 0 to 0.360. With increasing methanol, the ionization enthalpy for the first proton (ΔH₁) of HEPES increased steadily from 8.4 to 15.3 kJ mol⁻¹ whereas that for HEPPSO rose to a maximum of 21.0 kJ mol⁻¹ at X_m = 0.123 before dropping to 18.4 kJ mol⁻¹ at X_m = 0.360. The ionization enthalpy for the second proton (ΔH₂) of HEPES varied from 20.8 kJ mol⁻¹ in water to 13.6 kJ mol⁻¹ at X_m = 0.360 with a maximum of 24.8 kJ mol⁻¹ at X_m = 0.194. For HEPPSO, ΔH₂ increased steadily from 23.4 to 29.2 kJ mol⁻¹. The solvent composition was selected so as to include the region of maximum structure enhancement of water by methanol. The results were interpreted in terms of solvent-solvent and solvent-solute interactions.     

Regiospecific photoisomerization of fluorinated (E,E)-1,4-diphenyl-1,3-butadienes

Photoisomerization of five fluorinated E,E-1-(R-phenyl)-4-phenyl-1,3-butadienes in solution (R = 1: p-monofluoro, 2: m,m′-difluoro, 3: m,m′,p-trifluoro, 4: o,o′,m,m′-tetrafluoro, 5: o,o′,m,m′,p-pentafluoro) was investigated via direct irradiation. Our results indicated that cis-trans photoisomerization of the fluorinated 1,4-diphenyl-1,3-butadienes in the excited singlet state took place exclusively at the CC bonds closer to the fluorine substituents.     

Intermolecular Interactions in Binary Liquid Mixtures of Styrene with m-, o-, or p-xylene

The densities (ρ), ultrasonic speeds (ν), and refractive indices (n) of binary mixtures of styrene (STY) with m-, o-, or p-xylene, including those of their pure liquids, were measured over the entire composition range at the temperatures 298.15, 303.15, 308.15, and 313.15 K. The excess volumes (V^E), deviations in isentropic compressibilities (Δks), acoustic impedances (ΔZ), and refractive indices (Δn) were calculated from the experimental data. Partial molar volumes (V⁰_?,2) and partial molar isentropic compressibilities (K⁰_?,2) of xylenes in styrene have also been calculated. The derived functions, namely, V^E, Δk_s, ΔZ, Δn, V⁰_?,2, and K⁰_?,2 were used to have a better understanding of the intermolecular interactions occurring between the component molecules of the present liquid mixtures. The variations of these parameters suggest that the interactions between styrene and o-, m-, or p-xylene molecules follow the sequences: p-xylene>o-xylene>m-xylene. Apart from using density data for the calculation of VE, excess molar volumes were also estimated using refractive index data. Furthermore, several refractive index mixing rules have been used to estimate the refractive indices of the studied liquid mixtures theoretically. Overall, the computed and measured data were interpreted in terms of interactions between the mixing components.     

Conjugated linoleic acid determination in human milk by fast-gas chromatography

An efficient direct method for measuring c9,t11- and t10,c12-conjugated linoleic acid (CLA) isomer content in human and rat milk was developed and validated using an RTX-2330 capillary column (40 m × 0.18 mm × 0.1 μm). In comparison with the commonly used 100 m × 0.25 mm × 0.20 μm columns, this new type of fast column allowed the separation of FAMEs with the same resolution but in much less time. An additional advantage for biological samples was that only a small volume of sample was needed. Two different procedures were tested in order to select the best methylation of CLA isomers, and the alkali plus acid-catalyzed procedure was selected. The precision results showed relative standard deviations (R.S.D.) of repeatability and reproducibility ranging between 0.10 and 8.71%. The application of this method to human and rat milk samples showed that it was a rapid, simple and reliable method for the analysis of biological samples.     

The application of novel methodology for the synthesis of o-, m-, and p-(SF5-perfluoroethyl) benzene derivatives

The reaction of o-, m-, and p-F₂CCFC₆H₄X with SF₅Br produces an intermediate adduct, F₅SCF₂CFBrC₆H₄X, which, on treatment with AgBF₄, affords the first useful, high yield preparation of o-, m-, and p-F₅SCF₂CF₂C₆H₄X.     

Square wave adsorptive stripping voltametric determination of the mixture of nalidixic acid and its main metabolite (7-hydroxymethylnalidixic acid) by multivariate methods and artificial neural network

Nalidixic acid (NA) and its main metabolite, 7-hydroximethylnalidixic acid (OHNA), are quinolones antibacterial used as agents used for the treatment of urinary tract infection. For both compounds an adsorption process on a hanging mercury electrode (HMDE). On this basis, a square wave adsorptive stripping voltammetry (SWadSV) method has been developed for the individual and simultaneous determination of NA and OHNA. The variables that affect to accumulation process, such as concentration of perchloric acid, accumulation potential and accumulation time have been optimised by using an experimental design (concretely a Box-Behnken design with three levels) together with the response surface methodology (RSM). Calibration curves were linear in the range (0-1.38) × 10⁻⁷ mol L⁻¹ for NA and (0-3.23) × 10⁻⁸ mol L⁻¹ for OHNA, in the optimized conditions, with detection limits of 9.48 × 10⁻⁹ mol L⁻¹ and 8.06 × 10⁻¹⁰ mol L⁻¹ for NA and OHNA, respectively. The method was applied to urine samples containing only one of the analytes with satisfactory recoveries. As the voltammetric signals of these compounds show a high overlapping, different chemometric methods, such as classical least squares (CLS), partial least squares (PLS), principal component regression (PCR) and artificial neural network (ANN) have been used for the resolution of the mixture. The analysis of these compounds in urine samples were carried out using the different chemometric tools and the best recoveries were obtained by using ANN. No pre-treatment of the sample was necessary.     

Direct hydroxylation of substituted benzenes to phenols with air and CO using molybdovanadophosphates as a key catalyst

A direct synthetic method of cresols from toluene by hydroxylation with air using CO as a reducing agent was developed. The reaction of toluene with air (15 atm) and CO (5 atm) in the presence of catalytic amounts of H₄PMo₁₁VO₄₀·31H₂O and Pd/C in aqueous acetic acid at 120 °C for 2 h afforded a mixture of o-, m-, and p-cresols in 9.9% yield at 83% selectivity. Cresols were obtained in 19% yield by recharging air and CO under these conditions. A variety of substituted benzenes were hydroxylated by this method to give the corresponding phenol derivatives in higher selectivity.     

Chelating behavior of new chelating resins derived from n-(o-hydroxybenzyl)iminodiacetic acid

The chelating behavior of a new resin prepared by polycondensation of N-(o-hydroxybenzyl) iminodiacetic acid (o-HDA) with phenol and formaldehyde, is compared with that of the monomer, with p-HDA resin and p-HDA monomer, and with Chelex-100. The order of chelate stability for the o-HDA resin is Cu(II) > Ni(II) > Zn(II) > Co(II). An unusually high stability of the o-HDA and o-HDA resin iron(III) chelates in acidic solution is attributed to the participation of the o-hydroxyl group in the coordination process.     

Flow-injection catalytic spectrophotometic determination of molybdenum(VI) in plants using bromate oxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A novel flow-injection spectrophotometry has been developed for the determination of molybdenum(VI) at nanograms per milliliter levels. The method is based on the catalytic effect of molybdenum(VI) on the bromate oxidative coupling of p-hydrazinobenzenesulfonic acid with N-(1-naphthyl)ethylenediamine to form an azo dye (λ_max = 530 nm). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonic acid) acted as an effective activator for the molybdenum(VI)-catalyzed reaction and increased the sensitivity of the method. The reaction was monitored by measuring the change in absorbance of the dye produced. The proposed method allowed the determination of molybdenum(VI) in the range 1.0-20 ng mL⁻¹ with sample throughput of 15 h⁻¹. The limit of detection was 0.5 ng mL⁻¹ and a relative standard deviation for 10 ng mL⁻¹ molybdenum(VI) (n = 10) was 2.5%. The interfering ions were eliminated by using the combination of a masking agent and on-line minicolumn packed with cation exchanger. The present method was successfully applied to the determination of molybdenum(VI) in plant foodstuffs.