The proficiency testing programme for trace elements of the CORILA project

Harmonised quality schemes are being implemented in the framework of the thematic area Organization and Dissemination of Data of the Consorzio per la Gestione del Centro di Coordinamento delle Attività di Ricerca Inerenti il Sistema Lagunare di Venezia (Consortium for the Management of the Coordination Centre of Research Activities on the Venice Lagoon System, CORILA). Over the last 2 years, two proficiency tests were completed at the time of writing (while a third one is still in progress) to assess the capabilities of the analytical laboratories involved in the determination of trace elements in environmental inorganic matrices from the Lagoon of Venice.Both interlaboratorial trials were based on the determination of As, Cd, Cr, Cu, Fe, Hg, Pb and Zn in aqueous acidic, matrix-enriched solutions at concentrations within the ranges generally found in marine water and in sediment after chemical digestion, respectively. The proficiency of participants was assessed on the basis of the z score criterion (|z|≤2, acceptable results; 2<|z|<3, questionable results; |z|≥3, unacceptable results). In the two trials, the relevant percentages for the laboratories scoring |z|≤2 and |z|<3 were 61% and 71% and 65% and 77%, respectively. These first two proficiency tests, on the one hand, clearly pointed to the benefits the laboratories had from their participation in these exercises, and on the other hand, provided sound evidence of the need for further trials based on real environmental matrices.     

p-Aminobenzoate ion determination in pharmaceutical formulations by using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely, Pt|Hg|Hg₂(PABzt)₂| graphite, where PABzt stands for p-aminobenzoate ion, are described. This electrode responds to PABzt with sensivity of (58.1±1.0) mV per decade over the range 1.0×10⁻⁴ to 1.0×10⁻¹ mol l⁻¹ at pH 6.5-8.0 and a detection limit of 3.2×10⁻⁵ mol l⁻¹. The electrode shows easy construction, fast response time (within 10-30 s), low-cost, and excellent response stability (lifetime greater than 6 months, in continuous use). The proposed sensor displayed good selectivity for p-aminobenzoate in the presence of several substances, especially, concerning carboxylate and inorganic anions. It was used to determine p-aminobenzoate in pharmaceutical formulations by means of the standard additions method. The results obtained by using this electrode compared very favorably with those given by an HPLC procedure.     

Magnetic exchange interactions in perfluorophenyl dithiadiazolyl radicals

EPR, electrochemical studies and neutron diffraction studies on a large range of 1,2,3,5-dithiadiazolyl radicals have shown that the spin density distribution is essentially unaffected by substituent effects. The variation of magnetic properties previously reported for a series of perfluorophenyl-dithiadiazolyl radicals p-XC₆F₄CNSSN (X = CN, Br, NO₂ and NCC₆F₄) is therefore due to differences in molecular packing. The nearest-neighbour magnetic exchange interactions in these radicals are probed through DFT studies (B3LYP/6-311G**) and are shown to exhibit a variety of both ferromagnetic and antiferromagnetic interactions. All exchange interactions with |J| > 1 cm⁻¹ coincide with close heterocyclic contacts between dithiadiazolyl rings (3.18-4.00 Å) and produce |J| values up to 40 K. An analysis of these interactions indicates that the dominant exchange pathway would appear to be a direct exchange mechanism between radical centres, with orthogonality of the singly-occupied molecular orbitals (SOMOs) favouring ferromagnetic interactions.     

Synthesis, structure, and bridge-terminal alkyl exchange kinetics of pyrazolate-bridged dialuminum complexes containing bridging n-alkyl groups

Treatment of triethylaluminum with 3,5-diphenylpyrazole in a 2:1 stoichiometry afforded the ethyl-bridged complex Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ (79%) as a colorless crystalline solid. Treatment of tri-n-propylaluminum with 3,5-di-tert-butylpyrazole in a 2:1 stoichiometry afforded the n-propyl-bridged complex (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂ (63%) and the dimeric complex [(nPr)₂Al(μ-tBu₂pz)]₂ (3%), respectively, as colorless crystalline solids. Treatment of tri-n-propylaluminum (1 equiv.) or triisobutylaluminum (1 or 2 equiv.) with 3,5-di-tert-butylpyrazole afforded exclusively the dimeric complexes [(nPr)₂Al(μ-tBu₂pz)]₂ (68%) or [(iBu)₂Al(μ-tBu₂pz)]₂ (96%), respectively, as colorless crystalline solids. The solid state structures of Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ and (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂ consist of 3,5-disubstituted pyrazolato ligands with a di-n-alkylalumino group bonded to each nitrogen atom. An ethyl or n-propyl group acts as a bridge between the two aluminum atoms. The kinetics of the bridge-terminal exchange was determined for the bridging n-alkyl complexes by ¹³C NMR spectroscopy, and afforded ΔH^‡ = 1.5 ± 0.1 kcal/mol, ΔS^‡ = −46.8 ± 39.0 cal/K mol, and for Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ and ΔH^‡ = 1.7 ± 0.1 kcal/mol, ΔS^‡ = −46.6 ± 43.4 cal/K mol, and for (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂. The negative values of ΔS^‡ imply ordered transition states relative to the ground states, and rotation along the N-AlR₃ vector without aluminum-nitrogen bond cleavage is proposed.     

Interaction of polyhedral boron hydride anions [B10H10] and [B12H12] with cyclic copper and silver 3,5-bis(trifluoromethyl)pyrazolate complexes

The interactions of cyclic trinuclear copper {[3,5-(CF₃)₂Pz]Cu}₃ and silver {[3,5-(CF₃)₂Pz]Ag}₃ complexes with polyhedral borate anions [B₁₀H₁₀]²⁻ and [B₁₂H₁₂]²⁻ in solvents of low-polarity were studied using IR spectroscopy (190-290 K). Two types of complexes were found in solution: {[((3,5-CF₃)₂PzM)₃][B_nH_n]}²⁻ and {[((3,5-CF₃)₂PzM)₃]₂[B_nH_n]}²⁻ (M = Ag, Cu; n = 10, 12). The stability constants of these complexes were determined from IR-spectra.     

A green and sensitive method to determine phenols in water and wastewater samples using an aqueous two-phase system

A greener and more sensitive spectrophotometric procedure has been developed for the determination of phenol and o-cresol that exploits an aqueous two-phase system (ATPS) using a liquid-liquid extraction technique. An ATPS is formed mostly by water and does not require organic solvent. Other ATPS components used in this study were the polymer, polyethylene oxide, and some salts (i.e., Li₂SO₄, Na₂SO₄ or K₂HPO₄ + KOH). The method is based on the reaction between phenol, sodium nitroprusside (NPS) and hydroxylamine hydrochloride (HL) in an alkaline medium (pH 12.0), producing the complex anion [Fe₂(CN)₁₀]¹⁰⁻ that spontaneously concentrates in the top phase of the system. The linear range was 1.50-500 μg kg⁻¹ (R ≥ 0.9997; n = 8) with coefficients of variation equal to 0.38% for phenol and 0.30% for o-cresol (n = 5). The method yielded limits of detection (LODs) of 1.27 and 1.88 μg kg⁻¹ and limits of quantification (LOQs) of 4.22 and 6.28 μg kg⁻¹ for phenol and o-cresol, respectively. Recoveries between 95.7% and 107% were obtained for the determination of phenol in natural water and wastewater samples. In addition, excellent agreement was observed between this new ATPS method and the standard 4-aminoantipyrine (4-AAP) method.     

European ring exercise on water toxicity using different bioluminescence inhibition tests based on Vibrio fischeri, in support to the implementation of the water framework directive

An inter-laboratory comparison exercise was conducted under the European Union funded project entitled: Screening Methods for Water Data Information in Support of the Implementation of the Water Framework Directive (SWIFT-WFD) and coordinated by the Consejo Superior de Investigaciones Científicas (CSIC), in order to evaluate the reproducibility of different toxicity tests based on the bioluminescence inhibition of Vibrio fischeri, for the rapid water toxicity assessment.For the first time, this type of exercise has been organized in Europe, and using different tests based on the same principle. In this exercise, 10 laboratories from 8 countries (Austria, Cyprus, Germany, Greece, Italy, Portugal, Romania, and Spain) took place, and a total number of 360 samples were distributed.During the exercise, six series of six samples were analyzed along 5 months. Every batch of samples was composed by three real samples and three standard solutions. The real samples were: a raw influent and the effluent of a wastewater treatment plant (WWTP), and a sample from a first settlement of the WWTP spiked with a mixture of toxicant standards.A final number of 330 (91.7%) samples was analyzed, 3300 values in duplicate were collected, and the results for each sample were expressed as the 50% effective concentration (EC₅₀) values calculated through five points of dilution inhibition curves, after 5 and 15 min of incubation times.A statistical study was initiated using 660 results. The mean values, standard deviations (σ), variances (σ²), and upper and lower warning limits (UWL and LWL) were obtained, using the EC₅₀ values calculated with the result from the participating laboratories.The main objectives of this toxicity ring study were to evaluate the repeatability (r) and reproducibility (R) when different laboratories conduct the test, the influence of complex matrix samples, the variability between different tests based on the same principle, and to determine the rate at which participating laboratories successfully completed tests initiated.In this exercise, the 3.93% toxicity values were outliers according with the Z-score values and the Dixon test. The samples with the greater number of outliers were those with the smallest variability coefficient, corresponding to the greater and the smaller toxicity level.No relation was found through the cluster analysis, between the final results and the different commercial devices involved. Testing by multiple commercial devices did not appear to reduce the precision of the results, and the variability coefficient for the exercise was nearby to the average value for past editions carried out at national level, where the different participants used the same commercial device.Stability of samples was also followed during the exercise. While statistical significance differences were not found for the greater part of samples, for the sample from the WWTP influent, a significant decrease of the toxicity value was found along this study. Nevertheless, this was a type of sample with a high toxicity level during all the exercise.On the other hand, in order to obtain the chemical characterization of real samples, those were analyzed by chromatographic techniques, using different sequential solid phase extraction (SSPE) procedures, followed by liquid chromatography coupled with mass spectrometry (LC-MS), and gas chromatography-mass spectrometry (GC-MS). Good agreement was found between the chemical analysis results and the toxicity level of the samples.     

Determination of synthetic phenolic antioxidants and their metabolites in water samples by downscaled solid-phase extraction,silylation and gas chromatography–mass spectrometry

The development and performance evaluation of an analytical method dedicated to the comprehensive determination of the most relevant antioxidants and their metabolites in aqueous environmental samples is presented. This was achieved by a miniaturised solid-phase extraction (SPE) with 10 mg Oasis HLB cartridges, which allow to achieve a concentration factor of 200, reducing organic solvent wastes (1 mL of ethyl acetate suffices for complete elution) and SPE costs and eliminating the need for solvent evaporation that otherwise compromises the recoveries of butylated hydroxytoluene (BHT) and 2,6-di-tert-butylcyclohexa-2,5-diene-1,4-dione (BHT-Q). Analytes were then determined by gas chromatography–mass spectrometry (GC–MS) after derivatisation with N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA) in a single run. BHT-d₇ and n-propyl-paraben-d₄ (PrP-d₄) were used as surrogate internal standards. These surrogates allowed obtaining relative recoveries in the 80–110% range for all analytes even with complex wastewater samples and LODs at the 2–44 ng L⁻¹ level taking into account blank issues often associated to antioxidants analysis. The method was applied to sewage and river waters, showing that the seven analytes could be detected in raw wastewater. BHT and BHT-Q were the most concentrated species in that type of sample (in the 275–871 ng L⁻¹ range). On the other hand two metabolites of BHT, 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO) and 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) appeared to be the most ubiquitous species, being found in all samples in the 10–150 ng L⁻¹ concentration range.     

Combination of liquid-phase hollow fiber membrane microextraction with gas chromatography-negative chemical ionization mass spectrometry for the determination of dichlorophenol isomers in water and urine

A method for the determination of trace amount of dichlorophenol isomers in urine samples using the combination of liquid-phase hollow fiber microextraction (LPME-HF) with gas chromatography-negative chemical ionization mass spectrometry (GC-NCI-MS) has been demonstrated. The method has been optimized with respect to several parameters including the effects of negative chemical ionization (NCI) reagent pressure, the hollow fiber length, extraction time, stirring rate, sample pH and salt concentration for the determination of dichlorophenol isomers in water. The correlation coefficient (r²) of the calibration curves for 2,5-dichlorophenol, 2,3-dichlorophenol, 2,6-dichlorophenol, 3,5-dichlorophenol and 3,4-dichlorophenol were 0.988, 0.981, 0.985, 0.971 and 0.994, respectively. The average recovery rates for 2,5-dichlorophenol, 2,3-dichlorophenol, 2,6-dichlorophenol, 3,5-dichlorophenol and 3,4-dichlorophenol were 0.97, 0.93, 0.96, 0.95 and 0.95, respectively (n = 3 for each dichlorophenol) indicate that the methodology is feasible for the determination of trace amounts of dichlorophenol isomers in water and urine samples. Limits of detection (LOD) have been found to be in the range of 5-20 ng/ml. In addition, differentiation of the five dichlorophenol isomers is an easy task using the current approach of combining LPME-HF with NCI-GC-MS technique since they exhibit different NCI spectra.     

Aerobic oxidation of 1,3,5-triisopropylbenzene using N-hydroxyphthalimide (NHPI) as key catalyst

The first systematic study on the aerobic oxidation of 1,3,5-triisopropylbenzene was examined by the use of N-hydroxyphthalimide (NHPI) as a key catalyst. It was found that 1,3,5-triisopropylbenzene was efficiently oxidized with O₂ in the presence of a catalytic amount of NHPI and azobisisobutyronitrile (AIBN) at 75 °C. Upon treatment of the resulting products with sulfuric acid followed by acetic anhydride led to 5-acetoxy-1,3-diisopropylbenzene and 3,5-diacetoxy-1-isopropylbenzene as major products and a small amount of 1,3,5-triacetoxybenzene. When t-butylperoxypivalate (BPP) was employed as a radical initiator, the oxidation could be achieved in good yield even at 50 °C. This oxidation provides a facile method for preparing phenol derivatives bearing an isopropyl moiety, which can be used as pharmaceutical starting materials.     

Synthesis,characterization and crystal structure of a dioxomolybdenum(VI) complex with a N,O type bidentate Schiff base ligand as a catalyst for homogeneous oxidation of olefins

The synthesis of a Mo(VI) Schiff base complex, cis-[MoO₂{(4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenolate)₂}], cis-[MoO₂(L)₂] where L = 4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenol, derived from benzylamine and 3,5-di-tert-butylsalycilaldehyde is reported. Full characterization of this complex was accomplished with elemental analyses, spectroscopic studies (NMR, IR and electronic) and X-ray structure analysis. This complex was tested as a catalyst for the homogeneous oxidation of olefins. The Mo(VI) complex is catalytically active for the epoxidation of aliphatic substrates at 80 °C, yielding the epoxide as the sole product in yields up to 100% and turnover numbers up to 5000. Under the optimized conditions styrene was oxidized in an 81% conversion to produce styrene oxide, benzaldehyde, and acetophenone.     

Quantitative analysis of flavonoids and phenolic acids in Arnica montana L. by micellar electrokinetic capillary chromatography

Arnica montana preparations have been used in Europe for centuries to treat skin disorders. Among the biologically active ingredients in the flower heads of the plant are sequiterpenes, flavonoids and phenolic acids. For the simultaneous determination of compounds belonging to the latter two groups a micellar electrokinetic capillary chromatography (MEKC) method was developed and validated. By using an electrolyte solution containing 50 mM borax, 25 mM sodium dodecyl sulfate and 30% of acetonitrile the separation of seven flavonoids and four caffeic acid derivatives was feasible in less than 20 min. The optimized system was validated for repeatability (σ_rel ≤ 4.4%), precision (inter-day σ_rel ≤ 8.13%, intra-day σ_rel ≤ 4.32%), accuracy (recovery rates from 96.8 to 102.4%), sensitivity (limit of detection (LOD) ≤ 4.5 μg mL⁻¹) and linearity (R² ≥ 0.9996), and then successfully applied to assay several plant samples. In all of them the most dominant flavonoid was found to be quercetin 3-O-glucuronic acid, whereas 3,5-dicaffeoylquinic acid was the major phenolic acid; the total content of flavonoids and phenolic acids varied in the samples from 0.60 to 1.70%, and 1.03 to 2.24%, respectively.     

Determination of amines using 2-(11H-benzo[a]carbazol-11-yl) ethyl chloroformate (BCEC-Cl) as labeling reagent by HPLC with fluorescence detection and identification with APCI/MS

A pre-column derivatization method for the sensitive determination of amines using a labeling reagent 2-(11H-benzo[a]-carbazol-11-yl) ethyl chloroformate (BCEC-Cl) followed by high-performance liquid chromatography with fluorescence detection has been developed. Identification of derivatives was carried out by LC/APCI/MS in positive-ion mode. The chromophore of 1,2-benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC-Cl) reagent was replaced by 2-(11H-benzo[a]-carbazol-11-yl) ethyl functional group, which resulted in a sensitive fluorescence derivatizing reagent BCEC-Cl. BCEC-Cl could easily and quickly label amines. Derivatives were stable enough to be efficiently analyzed by HPLC and showed an intense protonated molecular ion corresponding m/z [M + H]⁺ under APCI/MS in positive-ion mode. The collision-induced dissociation of the protonated molecular ion formed characteristic fragment ions at m/z 261.8 and m/z 243.8 corresponding to the cleavages of CH₂O-CO and CH₂-OCO bonds. Studies on derivatization demonstrated excellent derivative yields over the pH 9.0-10.0. Maximal yields close to 100% were observed with three- to four-fold molar reagent excess. In addition, the detection responses for BCEC-derivatives were compared to those obtained using 1,2-benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC-Cl) and 9-fluorenyl methylchloroformate (FMOC-Cl) as labeling reagents. The ratios I_BCEC/I_BCEOC = 1.94-2.17 and I_BCEC/I_FMOC = 1.04-2.19 for fluorescent (FL) responses (here, I was relative fluorescence intensity). Separation of the derivatized amines had been optimized on reversed-phase Eclipse XDB-C₈ column. Detection limits calculated from 0.50 pmol injection, at a signal-to-noise ratio of 3, were 1.77-14.4 fmol. The relative standard deviations for within-day determination (n = 11) were 1.84-2.89% for the tested amines. The mean intra- and inter-assay precision for all amines levels were <3.64% and 2.52%, respectively. The mean recoveries ranged from 96.6% to 107.1% with their standard deviations in the range of 0.8-2.7. Excellent linear responses were observed with coefficients of >0.9996.     

A sensitive fluorescence reagent for the determination of aldehydes from alcoholic beverage using high-performance liquid chromatography with fluorescence detection and mass spectrometric identification

A pre-column derivatization method for the sensitive determination of aldehydes using the tagging reagent 2-[2-(7H-dibenzo[a,g] carbazol-7-yl)-ethoxy] ethyl carbonylhydrazine (DBCEEC) followed by high-performance liquid chromatography with fluorescence detection and APCI-MS identification has been developed. The chromophore of fluoren-9-methoxy-carbonylhydrazine (Fmoc-hydrazine) reagent was replaced by 2-[2-(7H-dibenzo[a,g] carbazol-7-yl)-ethoxy] ethyl functional group, which resulted in a sensitive fluorescence tagging reagent DBCEEC. DBCEEC could easily and quickly labeled aldehydes. The maximum excitation (300 nm) and emission (400 nm) wavelengths did not essentially change for all the aldehyde derivatives. Derivatives were sufficiently stable to be efficiently analyzed by high-performance liquid chromatography. The derivatives showed an intense protonated molecular ion corresponding m/z [M + (CH₂)_n]⁺ in positive-ion mode (M: molecular weight of DBCEEC, n: corresponding aldehyde carbon atom numbers). The collision-induced dissociation of protonated molecular ion formed fragment ions at m/z 294.6, m/z 338.6 and m/z 356.5. Studies on derivatization demonstrated excellent derivative yields in the presence of trichloroacetic acid (TCA) catalyst. Maximal yields close to 100% were observed with a 10 to 15-fold molar reagent excess. Separation of the derivatized aldehydes had been optimized on ZORBAX Eclipse XDB-C₈ column with aqueous acetonitrile as mobile phase in conjunction with a binary gradient elution. Excellent linear responses were observed at the concentration range of 0.01-10 nmol mL⁻¹ with coefficients of >0.9991. Detection limits obtained by the analysis of a derivatized standard containing 0.01 nmol mL⁻¹ of each aldehyde, were from 0.2 to 1.78 nmol L⁻¹ (at a signal-to-noise ratio of 3).     

Detection of DNA damaging agents using layer-by-layer assembly

The layer-by-layer (LBL) electrostatic deposition method was used to fabricate multilayer films of pentaerythritol-based metallodendrimer with Ru^II terpyridine subunits (RuDen) that has a positive charge and ds-DNA (ds, double-stranded) that has a negative charge due to its phosphate backbone. Evidence of assembly was obtained by fabrication of (DNA | RuDen)_n on quartz treated with poly(diallyldimethylammonium chloride), PDDA. The absorbance at 263 nm varied linearly with n in the range 1-6. For electrochemical monitoring of damage by styrene oxide, the assembly was on a glassy carbon electrode that was coated with a monolayer of aminobenzoic acid. The measurement was based upon the RuDen-catalyzed oxidation of sites, e.g. guanine, that are exposed when ds-DNA is damaged. The peak current at 1.07 V versus Ag | AgCl in square wave voltammetry increases with incubation time for 30 min. The process was also monitored by the shift in the spectrum of a long period grating (LPG) fiber coated with (DNA | RuDen)₅. A typical shift, which is due to changes in the refractive index of the coating, was 0.3 and 1.8 nm for 5 and 30 min exposures, respectively, using an algorithm that can measure a shift of 10⁻⁴ nm.     

Dioxouranium(VI)-carboxylate complexes: A calorimetric and potentiometric investigation of interaction with oxalate at infinite dilution and in NaCl aqueous solution at I = 1.0 mol L and T = 25 °C

In this paper we investigated the interactions between dioxouranium(VI) and oxalate using (H⁺-glass electrode) potentiometry and titration calorimetry. Potentiometric measurements were carried out in NaCl aqueous solutions and at T = 25 °C in a wide range of experimental conditions (concentrations, ligand/metal molar ratio, pH, titrants) at low ionic strength values (I ≤ 0.090 mol L⁻¹, without supporting electrolyte) and at I = 1.0 mol L⁻¹; different procedures were employed for the acquisition of experimental data and careful analysis of these data performed. In all cases the speciation model that best fits experimental data takes into account the formation of the binary mononuclear species UO₂(ox)⁰, UO₂(ox)₂²⁻, UO₂(ox)₃⁴⁻ widely reported in literature, the ternary hydroxyl mononuclear species UO₂(ox)OH⁻, UO₂(ox)(OH)₂²⁻, UO₂(ox)₂OH³⁻, UO₂(ox)₃OH⁵⁻, the protonated ternary mononuclear species UO₂(ox)₃H³⁻ and the binuclear species (UO₂)₂(ox)₅⁶⁻.Calorimetric measurements were carried out following similar procedures and in the same experimental conditions as employed for the potentiometric measurements at I = 1.0 mol L⁻¹ in NaCl. The stability of UO₂²⁺-oxalate²⁻ complexes is fairly high and their main contribution to stability is entropic in nature. Some linear empirical relationships were found which make it possible to calculate (i) the contribution of a single bond: and ; (ii) chelate stabilisation per ring: and and (iii) the mean stability of negatively charged Na⁺-ion pair complexes: log^TK = (0.46 ± 0.02)·|z| (z = charge of complex species), ΔG° = −(2.60 ± 0.1)·|z| kJ mol⁻¹ and TΔS° = 2.5 ± 0.5 kJ mol⁻¹. Both potentiometric and calorimetric results provide evidence of the penta-coordination of the species UO₂(ox)₃⁴⁻. SIT parameters were calculated from the data at I = 0 and I = 1.02 mol kg⁻¹. Comparisons are made with literature data. An insoluble dioxouranium(VI) ternary complex was synthesised (at I = 1.0 mol L⁻¹ in NaCl) and characterised by thermoanalysis and elemental analysis.     

Determination of anethole trithione in human plasma using high performance liquid chromatography coupled with tandem mass spectrometric detection

A rapid, sensitive and reliable high performance liquid chromatographic method coupled with tandem mass spectrometry via electrospray ionization (ESI) source (HPLC-MS/MS) has been developed and validated for the determination of anethole trithione (ATT) in human plasma. Diazepam was employed as the internal standard (IS). Sample extracts following liquid-liquid extraction were injected into the HPLC-MS/MS system. The analyte and IS were eluted isocratically on a C₁₈ column, with a mobile phase consisting of methanol and aqueous ammonium acetate solution (5 mM) (80:20, v/v) .The ions were detected by a triple quadrupole mass spectrometric detector in the positive mode. Quantification was performed using selected reaction monitoring (SRM) of the transitions m/z 240.88 → 197.91 and m/z 285.01 → 193.02 for ATT and for the IS, respectively. The analysis time for each run was 5.0 min. The calibration curve fitted well over the concentration range of 0.02-5 ng mL⁻¹, with the regression equation y = 1.1014x + 0.0003631, r = 0.9992. The intra-batch and inter-batch R.S.D.% were less than 15% at all concentration levels within the calibration range. The recoveries were more than 80%. The present method provides a modern, rapid and robust procedure for the pharmacokinetic study of ATT. Some important pharmacokinetic parameters of ATT in healthy Chinese volunteers are also given for the first time.     

Phenol derivatized hexahydropyrimidines prepared from Mannich condensations

Six new phenol derivatized hexahydropyrimidines (1,3-bis-(2-hydroxy-3,5-di(X)benzyl) hexahydropyrimidine and 5,5′-dimethyl-1,3-bis-(2-hydroxy-3,5-di(X)benzyl) hexahydropyrimidine where X = Me, t-Bu, and Cl) were synthesized in one-pot in 33-79% yield using Mannich condensations.     

Simultaneous measurement of trace monoadenosine and diadenosine monophosphate in biomimicking prebiotic synthesis using high-performance liquid chromatography with ultraviolet detection and electrospray ionization mass spectrometry characterization

The method for simultaneous separation and determination of trace monoadenosine and diadenosine monophosphate (i.e. 2′-AMP, 3′-AMP, 5′-AMP and 3′-5′ ApA) in biomimicking prebiotic synthesis was developed using high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection and electrospray ionization mass spectrometry (ESI-MS) identification. The separation was performed on a Supelco C₁₈ column with a gradient elution (solvent A: 10 mM NH₄Ac aqueous solution; solvent B: MeOH). The flow rate was set at 1.0 ml/min. The quantitative determination was achieved by HPLC with UV detection at 260 nm. The linearity ranged from 0.5 to 100 μg/ml for each nucleotide. The limits of detection (LODs) for the four nucleotides were less than 0.30 μg/ml. The recovery ranged from 95.2 to 100.7%. The intra-day relative standard deviations (RSDs) of the retention times were between 0.7 and 1.1%. Both full-scan ESI-MS and -MS² for the four nucleotides under both positive and negative polarity were carried out and the possible cleavage pathways of them were depicted. The specific ions, [AMP + H]⁺ at m/z 348 and [ApA + H]⁺ at m/z 597, were chosen to characterize the four nucleotides in biomimicking prebiotic synthesis between N-(O,O-diisopropyl) phosphoryl amino acid (Dipp-aa) and adenosine. Using the proposed HPLC/UV/ESI-MS method, the concentration of 2′-AMP, 3′-AMP, 5′-AMP and 3′-5′ ApA in the biomimicking prebiotic synthesis samples were determined.     

Characterization of steroidal saponins in crude extract from Dioscorea nipponica Makino by liquid chromatography tandem multi-stage mass spectrometry

The liquid chromatography-electrospray ionization-tandem multi-stage mass spectrometry (LC-ESI-MSⁿ) method was developed for the analyses and characterization of steroidal saponins in plant extract from the rhizome of Dioscorea nipponica Makino. The HPLC experiments were performed by means of a reversed-phase C₁₈ column and a binary mobile phase system consisting of water and acetonitrile under gradient elution conditions. Pseudoprotodioscin, methyl protodioscin and dioscin were identified by comparing the retention times, UV spectra and the fragmentation properties of [M − H]⁻ ions with the authentic standards. Four groups of steroidal saponin isomers possessed the [M − H]⁻ ions at m/z 1063, 1045, 901 and 1047, respectively, were observed during the LC-ESI(−)-MS analysis, and three groups of them except the pair of isomers with the [M − H]⁻ ions at m/z 1047 could be differentiated by LC-ESI(−)-MS³. Furthermore, the ESI-MSⁿ fragmentation behaviors of the [M + Li]⁺ ions of pseudoprotodioscin and methyl protodioscin have been investigated, and the observed information helped the structural elucidation of the more abundant isomer with the [M − H]⁻ ion at m/z 1047. As the result, a special sugar sequence of the saccharide chains was observed that not glucose but rhamnose might be connected with the hydroxyl group at C-3 position of the steroidal aglycone.