Determination of unsulfonated aromatic amines in FD&C Yellow No. 6 by the diazotization and coupling procedure followed by reversed-phase high-performance liquid chromatography

Data are presented for the determination of parts-per-billion (10(9)) levels of aniline, benzidine, 4-aminobiphenyl (4-ABP) and 4-aminoazobenzene in the regulated color additive FD&C Yellow No. 6. The determination involves chloroform extraction of the amines from the color additive, followed by diazotization and coupling with the disodium salt of 3-hydroxy-2,7-naphthalenedisulfonic acid (R-salt). The coupling products are then analyzed by reversed-phase high-performance liquid chromatography. An interference discovered during the determination of 4-ABP required the use of 4,5-dihydro-5-oxo-1-(4-sulfophenyl)-1H-pyrazole-3-carboxylic acid (pyrazolone-T) as an alternative coupling agent. The identity of each coupling product is confirmed by obtaining a UV-visible spectrum of the eluting solute. The liquid chromatograph is calibrated in the presence of the color additive by using the external standard method.     

Significance of chemical enhancement effects in surface-enhanced Raman scattering (SERS) signals of aniline and aminobiphenyl isomers

Surface-enhanced Raman scattering is a useful technique for detecting low levels of aromatic amines as environmental contaminants because it can be used to detect and distinguish among their isomers based on their distinctive SERS spectra. This paper demonstrates the feasibility of measuring the concentrations of aminobiphenyls (ABPs) including 4-ABP, 3-ABP, and 2-ABP down to the levels of about 5, 50, and 250 μg/mL, respectively. The SERS signal intensities of ABPs are dependent on the pH values of the samples and colloidal media. The optimal sample pH values were found to be 6.86, 7.83, and 7.36, for 2-ABP, 3-ABP, and 4-ABP, respectively, whereas the optimum silver colloidal pH ranges from 5.0 to 6.5. A detailed analysis of the different vibrational modes of aniline and the ABP isomers was carried out using computational modeling based on the density functional theory (DFT). Compared to aniline, the ABPs produced greater SERS enhancement of the intensities for the biphenyl ring-breathing mode. The SERS signal for the NH₂ wagging band shows the order of enhancement as given by 4-ABP > 2-ABP > 3-ABP, which correlates well with the HOMO-LUMO energy gap based on the DFT modeling of the amines adsorbed on the silver cluster.     

Further application of the diazotizationcoupling spectrophotometric technique to the determination of aromatic amines with 8-amino-1 -hydroxynaphthalene-3,6-disulphonic acid and N-(1-naphthyl)-ethylenediamine as coupling agents

Twenty-two aromatic amines are determined by the diazotization-coupling spectrophotometric technique, using 8-amino-1-hydroxynaphthalene-3,6-disulphonic acid (H-acid) and N-(1-naphthyl) ethylenediamine (N-na) as coupling agents. The following are determined by both methods: 2-and 4-ethylaniline, 4-aminobenzonitrile, 3- and 4-aminoacetophenone, 4-aminobenzophenone, 4-iodoaniline, 2,5-dichloroaniline, 4-aminohippuric acid, 2-aminobenzyl alcohol, 3-aminobenzamide, sulphathiazole, 2-, 3- and 4-methoxyaniline and 2,4-, 3,4- and 3,5-dimethylaniline. It is possible to determine 2,3- and 2,5-dimethylaniline only by the H-acid method, but 2,6-dimethylaniline cannot be determined by either method. 2-Aminobenzamide can only be determined by the N-na method. In the application of the H-acid method to the methoxyanilines and dimethylanilines, the colour is developed by adding a large excess of sodium bicarbonate and H-acid. In the application of the N-na method to the ethylanilines, methoxyanilines and 2,4-, 3,4- and 3,5-dimethylanilines, the colour is developed by addition of a large excess of N-na reagent and allowing the solution to stand overnight.     

Ab initio quantum chemical investigation of intramolecular magnetic interaction in some diradical derivatives of imino nitroxide and nitronyl nitroxide

The magnetic properties of the monoradicals 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl (1) and 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide (2) and the diradicals 2,2'-(1,2-ethynediyldi-4,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (3), 2,2'-(1,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (4), and 2,2'-(1,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide] (5) are investigated by ab initio quantum chemical methods. The rule of spin alternation in the unrestricted Hartree-Fock (UHF) method clearly shows that the radical sites are antiferromagnetically coupled in 3 and ferromagnetically coupled in 4 and 5, which is consistent with a previous experiment. The molecular geometries are optimized at Hartree-Fock levels. This is followed by single-point calculations using the density functional (UB3LYP) treatment and the multiconfigurational complete active space self-consistent field (CASSCF) methodology. Magnetic exchange coupling constants are determined from the broken-symmetry approach. The calculated J values, -3.60 cm(-1) for 3, 0.16 cm(-1) for 4, and 0.67 cm(-1) for 5, are in excellent agreement with the observed values. Because of the very large size of the diradicals 3-5, the CASSCF (10,10) calculations cannot yield realistic J values. Nevertheless, the CASSCF calculations support the antiferromagnetic nature of the magnetic coupling in 3 and the ferromagnetic nature of the coupling in 4 and 5. The existence of an intramolecular magnetic coupling in 3-5 is also confirmed through computations of the isotropic hyperfine coupling constants for monoradicals 1 and 2 as well as diradicals 3-5.     

An improved liquid chromatography–tandem mass spectrometry method for the quantification of 4-aminobiphenyl DNA adducts in urinary bladder cells and tissues

Exposure to 4-aminobiphenyl (4-ABP), an environmental and tobacco smoke carcinogen that targets the bladder urothelium, leads to DNA adduct formation and cancer development [1]. Two major analytical challenges in DNA adduct analysis of human samples have been limited sample availability and the need to reach detection limits approaching the part-per-billion threshold. By operating at nano-flow rates and incorporating a capillary analytical column in addition to an online sample enrichment step, we have developed a sensitive and quantitative HPLC–MS/MS method appropriate for the analysis of such samples. This assay for the deoxyguanosine adduct of 4-ABP (dG-C8-4-ABP) gave mass detection limits of 20 amol in 1.25 μg of DNA (5 adducts in 10⁹ nucleosides) with a linear range of 70 amol to 70 fmol. 4-ABP-exposed human bladder cells and rat bladder tissue were analyzed in triplicate, and higher dose concentrations led to increased numbers of detected adducts. It was subsequently established that sample requirements could be further reduced to 1 μg digestions and the equivalent of 250 ng DNA per injection for the detection of low levels of dG-C8-4-ABP in a matrix of exfoliated human urothelial cell DNA. This method is appropriate for the characterization and quantification of DNA adducts in human samples and can lead to a greater understanding of their role in carcinogenesis and also facilitate evaluation of chemopreventive agents.     

Spectrophotometric determination of hydroxylamine and its derivatives in pharmaceuticals

A sensitive spectrophotometric method for the determination of hydroxylamine is described. The method is based on the oxidation of hydroxylamine to nitrite using sodium arsenate under alkaline condition. The formed nitrite is determined based on the diazo coupling reaction between p-nitroaniline and N-(1-naphthyl)ethylenediamine dihydrochloride [NEDA]. The system obeys Beer's law over the concentration range 0-7 microg of hydroxylamine at 545 nm and the colour is stable for 3 h. The molar absorptivity of the colour system is found to be 6.7 x 10(4) l mol(-1) cm(-1). The relative standard deviation is 1.2% for ten determinations at 4 microg of hydroxylamine. Interferences due to various foreign ions have been studied and the method has been applied to the determination of hydroxylamine and its derivatives used in pharmaceutical formulations after hydrolysis.     

Carbon-carbon bond formation of alkenylphosphonates by aldehyde insertion into zirconacycle phosphonates

Ethyl 1-butynylphosphonate reacts with Cp(2)ZrCl(2)/2n-BuLi to give a three-membered zirconacycle that readily inserts aldehydes. Hydrolysis of the intermediate five-membered zirconacycles leads to two products, 4 and 5. In the major product, 5, the aldehyde inserts into C2 of the zirconacycle, while in the minor product, 4, the aldehyde inserts into C1. Products 5 are obtained in 38-75% isolated yields. Products 4 are obtained in approximately 1-12%. Essentially, only compounds 5 are produced with ortho-substituted aldehydes. The regio- and stereochemistry of 4 and 5 were determined by (3)J(PH), (2)J(PC2), and (3)J(PC3) coupling constants.     

Spectrophotometric determination of tryptophan by reaction with nitrous acid

The heterocyclic nucleus in tryptophan is oxidised by nitrous acid at elevated temperature to produce a phenolic intermediate which further reacts with nitrous acid to form a nitro compound that has a golden yellow colour in alkaline medium. The maximum absorbance is obtained at 400 nm with maximum molar absorptivity of 9.44 x 10(3) l.mole(-1). cm(-1). Derivatives of tryptophan such as indole-3-acetic acid, tryptamine and tryptophanamide, as well as indole, produce the same colour, but some others, e.g., 5-hydroxytryptamine and 5-hydroxyindole-3-acetic acid do not give the colour reaction. A plausible mechanism is proposed to explain this behaviour.     

4-(3,5-dichloro-2-pyridylazo)-1,3-diaminobenzene as a metallochromic indicator for the complexometric determination of Cu(II) with EDTA

In slightly acid solutions Cu(II) and 4-(3,5-dichloro-2-pyridylazo)-1,3-diaminobenzene (3,5-C12PADAB) form a red-purple complex( = 5.0 x 10(4)1.mole(-). cm(-1) at 547 nm). The complex is readily broken by EDTA, with a sharp change of colour to the yellow of the free reagent (Deltalambda(max) = 110 nm at pH 3.5). This colour contrast and the reversibility of the formation reaction, together with the solubility of the complex in water, make the pyridylazo reagent useful as a metallochromic indicator for copper titration, at pH 2.7-5.5. The Cu(II)-3,5-C12PADAB indicator system has been satisfactorily applied to the determination of sulphur in cast iron, "useful oxides" (Al(2)O(3) + Fe(2)O(3)) in samples of commercial aluminium sulphate, and total phosphorus in a synthetic mixed fertilizer.     

The bending vibrational levels of the acetylene cation: a case study of the Renner-Teller effect in a molecule with two degenerate bending vibrations

Forty three vibronic levels of C2H2+, X 2Pi u, with upsilon4 = 0-6, upsilon5 = 0-3, and K = 0-4, lying at energies of 0-3520 cm(-1) above the zero-point level, have been recorded at rotational resolution. These levels were observed by double resonance, using 1+1' two-color pulsed-field ionization zero-kinetic-energy photoelectron spectroscopy. The intermediate states were single rovibrational levels chosen from the A1Au, 4nu3 (K = 1-2), 5nu3 (K = 1), nu2+4nu3 (K = 0), and 47,206 cm(-1) (K = 1) levels of C2H2. Seven of the trans-bending levels of C2H2+ (upsilon4 = 0-3, K = 0-2) had been reported previously by Pratt et al. [J. Chem. Phys. 99, 6233 (1993)]; our results for these levels agree well with theirs. A full analysis has been carried out, including the Renner-Teller effect and the vibrational anharmonicity for both the trans- and cis-bending vibrations. The rotational structure of the lowest 16 vibronic levels (consisting of the complete set of levels with upsilon4 + upsilon5 < or = 2, except for the unobserved upper (2Pi u component of the 2nu4 overtone) could be fitted by least squares using 16 parameters to give an rms deviation of 0.21 cm(-1). The vibronic coupling parameter epsilon5 (about whose magnitude there has been controversy) was determined to be -0.0273(7). For the higher vibronic levels, an additional parameter, r45, was needed to allow for the Darling-Dennison resonance between the two bending manifolds. Almost all the observed levels of the upsilon4 + upsilon5 = 3 and 4 polyads (about half of the predicted number) could then be assigned. In a final fit to 39 vibronic levels with upsilon4 + upsilon5 < or = 5, an rms deviation of 0.34 cm(-1) was obtained using 20 parameters. An interesting finding is that Hund's spin-coupling cases (a) and (b) both occur in the Sigmau components of the nu4 + 2nu5 combination level. The ionization potential of C2H2 (from the lowest rotational level of the ground state to the lowest rotational level of the cation) is found to be 91,953.77 +/- 0.09 cm(-1) (3sigma).     

The Jahn-Teller effect in CH3Cl+(X̃2E): a combined high-resolution experimental measurement and ab initio theoretical study

The energy levels of CH(3)Cl(+)X?(2)E showing strong spin-vibronic coupling effect (Jahn-Teller effect) have been measured up to 3500 cm(-1) above the ground vibrational state using one-photon zero-kinetic energy photoelectron and mass-analyzed threshold ionization spectroscopic method. Theoretical calculations have been also performed to calculate the spin-vibronic energy levels using a diabatic model and ab initio adiabatic potential energy surfaces (PESs). In the theoretical calculations the diabatic potential energy surfaces are expanded by the Taylor expansions up to the fourth-order including the multimode vibronic interactions. The calculated spin-orbit energy splitting (224.6 cm(-1)) for the ground vibrational state is in good agreement with the experimental data (219 ± 3 cm(-1)), which indicates that the Jahn-Teller and the spin-orbit coupling have been properly described in the theoretical model near the zero-point energy level. Based on the assignments predicted by the theoretical calculations, the experimentally measured energy levels were fitted to those from the diabatic model by optimizing the main spectroscopic parameters. The PESs from the ab initio calculations at the level of CASPT2/vq(t)z were thus compared with those calculated from the experimentally determined spectroscopic parameters. The theoretical diagonal elements in the diabatic potential matrix are in good agreement with those determined using the experimental data, however, the theoretical off-diagonal elements appreciably deviate from those determined using the experimental data for geometric points far away from the conical intersections. It is also concluded that the JT effect in CH(3)Cl(+) mainly arises from the linear coupling and the mode coupling between the CH(3) deform (υ(5)) and CH(3) rock (υ(6)) vibrations. The mode couplings between the symmetric C-Cl stretching vibration υ(3) with υ(5) and υ(6) are also important to understand the spin-vibronic structure of the molecule.     

Synthesis and properties of novel oligothiophenes surrounded by bicyclo[2.2.2]octene frameworks

Novel oligothiophenes surrounded by bicyclo[2.2.2]octene (abbreviated as BCO) frameworks ranging from dimer to hexamer, 1(nT) (n = 2, 3, 4, 6), were prepared, and their structures and electronic properties were investigated. Dimer 1(2T) was synthesized by oxidative coupling of the 2-lithiated monomer generated from 4,5-BCO-annelated 2-bromothiophene 8 with CuCl2 in 76% yield. Trimer 1(3T) and tetramer 1(4T) were synthesized by Stille coupling of 2,5-dibromo-3,4-BCO-annelated thiophene 4 and of the 5,5'-dibromo derivative of bis(3,4-BCO-thiophen-2-yl) 10 with 2-stannylated 4,5-BCO-annelated thiophene 9 in 41% and 46% yield, respectively. Hexamer 1(6T) was synthesized by oxidative coupling of terthiophene 12, tris-annelated with BCO units, in 81% yield. X-ray crystallographic studies showed that the thiophene rings in 1(2T) and 1(3T) are rotated around the inter-ring C-C bond(s) with the C=C-C=C dihedral angles of -174.3(5) degrees for 1(2T) and -149.7(3) degrees and 34.4(3) degrees for 1(3T). In the crystal structures of 1(2T) and 1(3T), no pi-stacking was observed as expected from the steric effect of the BCO units. Theoretical calculations for 1(2T) and 1(3T) at the B3LYP/6-31G(d) level indicated that the annelation with BCO units either at the 2,3- or 3,4-positions of thiophene rings raises both the KS HOMO and LUMO levels. In the electronic absorption spectra of 1, the longest wavelength absorption band corresponding to the pi-pi transition is bathochromically shifted with the increase in absorption intensity as the number of thiophene rings increases, and the absorption of the polythiophene 1 with infinite length was predicted to be 419 nm. The cyclic voltammetry of 1 in CH2Cl2 at -78 degrees C (2T) or at room temperature (3T, 4T, 6T) showed two reversible oxidation waves, indicating that the radical cation and dication of 1 are stable under these conditions.     

Different supramolecular hydrogen bond structures and significant changes in magnetic properties in dinuclear mu 2-1,1-N3 copper(II) complexes with very similar tridentate Schiff base blocking ligands

Three new basal-apical, mu(2)-1,1-azide bridged complexes, [CuL(1)(N(3))](2) (1), [CuL(2)(N(3))](2) (2) and [CuL(3)(N(3))](2) (3) with very similar tridentate Schiff base blocking ligands [L(1) = N-(3-aminopropyl)salicylaldimine, L(2) = 7-amino-4-methyl-5-azahept-3-en-2-one and L(3) = 8-amino-4-methyl-5-azaoct-3-en-2-one) have been synthesised and their molecular structures determined by X-ray crystallography. In complex 1, there is no inter-dimer H-bonding. However, complexes 2 and 3 form two different supramolecular structures in which the dinuclear entities are linked by strong H-bonds giving one-dimensional systems. Variable-temperature (300-2 K) magnetic susceptibility measurements and magnetization measurements at 2 K reveal that complexes and have antiferromagnetic coupling while has ferromagnetic coupling which is also confirmed by EPR spectra at 4-300 K. Magnetostructural correlations have been made taking into consideration both the azido bridging ligands and the existence of intermolecular hydrogen bonds in complexes 2 and 3.     

New regiospecific isothiazole C-C coupling chemistry

Regioselective palladium catalysed coupling reactions are achieved in good to high yields, starting from either 3,5-dichloro- or 3,5-dibromoisothiazole-4-carbonitriles 1 and 2, providing 3-halo-5-(hetero/aryl, alkenyl and alkynyl)isothiazoles 3, 4, 6-9 from Stille couplings, 3-halo-5-(hetero/arylethynyl)isothiazoles 14-19 from Sonogashira and 5,5'-bi(3-chloroisothiazole-4-carbonitrile) (13) from an Ullmann type coupling. 3,5-Dibromoisothiazole-4-carbonitrile 2 is more reactive than the dichloroisothiazole-4-carbonitrile 1 and effective enough for Stille, Negishi and Sonogashira couplings. 5,5-Bi(3-chloroisothiazole-4-carbonitrile) (13) is prepared by a palladium catalysed Ullmann coupling from 3-chloro-5-iodoisothiazole-4-carbonitrile (11). A variety of 3-substituted isothiazoles (3-substituents = Cl, Br, OMs, OTs and OTf) are less reactive and fail to give successful Suzuki couplings at the isothiazole C-3 position. The 3-iodo-5-phenyl-isothiazole-4-carbonitrile (28), prepared via Sandmeyer iodination, participates successfully in Suzuki, Ullmann type, Stille, Negishi and Sonogashira coupling reactions. All products are fully characterized.     

Polarographic behaviour and determination of acrivastine in capsules and human urine

Dibenzo-18-crown-6 (DB18C6) is used for the liquid-liquid extraction, and recovery of titanium from paints, pigment, paper and pulp industries. The extraction mechanism of titanium(IV) from pH 4 medium with DB18C6 in dichloromethane was investigated. The DB18C6 concentration in organic phase, the concentration of titanium, the effect of pH and interference ions such as Mo(6+), V(5+), Nb(5+), Ta(5+), Zr(4+), Fe(3+), etc. in the aqueous phase and the temperature on the distribution coefficient for the Ti(IV) have been examined. The titanium was determined by spectrophotometric and inductively coupled plasma atomic emission spectroscopic (ICP-AES) method. Titanium forms a colourless complex with DB18C6 at pH 4.0 which is extracted with dichloromethane having molar absorptivity 1.53x10(4) lmol(-1)cm(-1) at 285 nm. It obeys Beer's law in the range of 0.16-3.84 ppm of titanium. The colour was developed with thiocyanate which has molar absorptivity 1.50x10(3) lmol(-1)cm(-1) at 425 nm. The extract is directly inserted in the plasma for ICP-AES measurement, which enhance the sensitivity several folds and the limits for estimation are 0.5-30 ngml(-1). The overall formation (logbeta(2)K'e) and extraction (K(ex)) constants calculated are 18.61+/-0.02 and 1.03+/-0.03x10(-10), respectively. The transportation of titanium has been discussed. The titanium is preconcentrated and determined in standard and environmental samples.     

可聚合型光引发剂4-丙烯酰氧基二苯甲酮的光聚合性能研究

以实时红外光谱(RT-IR)法研究了合成的4-丙烯酰氧基二苯甲酮(4-ABP)的光聚合动力学性质,考察了不同单体、不同引发剂和助引发剂浓度、不同光强对聚合性能的影响.以萃取法对比研究了4-ABP和二苯甲酮(BP)在固化膜中的的残留量.结果表明,4-ABP是一种非常有效的光引发剂.随着引发剂浓度和光强的增大,单体转化率、最大反应速率都增大,诱导期缩短.萃取实验表明4-ABP在固化膜中的残留量远低于BP.     

The surfactant-sensitized analytical reaction of niobium with 8-hydroxyquinoline-5-sulphonic acid

Cationic surfactants, such as cetylpyridinium bromide (CPB), sensitize the colour reaction of Nb(V) with 8-hydroxyquinoline-5-sulphonic acid (H(2)L). The formation of a ternary complex of stoichiometry 1:3:3 (Nb-L-CPB) is responsible for the observed enhancement in absorptivity and the quenching in the fluorescence of the Nb-L chelate, when a surfactant is present. The ternary complex exhibits maximum absorption at 383 nm ( = 1.46 +/- 0.01 x 10(4) l.mole(-1).cm(-1)) at pH 5.7, and Beer's law is obeyed up to 6-mug ml Nb concentration. Conditional formation constants of the niobium chelate in the presence and absence of CPB have been determined. On the basis of a detailed spectrophotometric and fluorimetric study the nature of the chromophoric reagent-surfactant interaction and the peculiar features of the sensitization by CPB are discussed.     

Potentiometric flow injection determination of amylase activity by using hexacyanoferrate(III)-hexacyanoferrate(II) potential buffer

A highly sensitive potentiometric flow injection determination of amylase activity was carried out, utilizing a redox reaction of hexacyanoferrate(III) in alkaline media with reducing sugar as product of the enzymatic hydrolysis reaction of starch with amylase. The analytical method is based on the potential change detection of a flow-through type redox electrode detector due to the composition change of a [Fe(CN)(6)](3-)-[Fe(CN)(6)](4-) potential buffer solution, which is caused by the redox reaction with the product of the enzymatic reaction. A linear relationship exists between the potential change (peak height) and the activity of amylase. Amylase of a wide activity range from 2.5x10(-2) to 1.2x10(-4) U ml(-1) can be determined by the changing the concentrations of the [Fe(CN)(6)](3-)-[Fe(CN)(6)](4-) potential buffer from 10(-3) to 10(-5) M. The lower detection limit of amylase activity is 6.0x10(-5) U ml(-1). The sampling rate and relative standard deviation are 15 h(-1) and 0.9% (n=5) for 3.8x10(-3) U ml(-1) of amylase. The present method was successfully applied to determine amylase activity in real samples (commercial digestive medicines) with an accuracy of 4% compared with analytical results obtained using the present method with those achieved using the conventional titration method.     

Flexibility of CuCl4-tetrahedra in bis[cinchoninium tetrachlorocuprate(II)]trihydrate single crystals. X-ray diffraction and EPR studies

Crystal structure of bis[cinchoninium tetrachlorocuprate(II)] trihydrate, [(C19H24N2O)CuCl4]2-3H2O, has been determined by X-ray diffraction at 100 K and reexamined at 293 K. The compound crystallizes in orthorhombic system with a P2(1)2(1)2(1) space group and unit cell parameters a = 15.3031(14), b = 36.415(3), and c = 7.8341(5) A at 100 K, and Z = 4. The asymmetric unit consists of two (CuCl4)(2-) tetrahedral anions linked by hydrogen bonds to two doubly protonated cinchonine molecules and three water molecules. The tetrahedra are strongly flattened, to approximately D(2d) symmetry, with different deformation for two inequivalent (CuCl4)(2-) -ions in the asymmetric unit. The deformation of (CuCl4)(2-) and cinchoninium cations varies with temperature due to a rearrangement of the bifurcated hydrogen bond network. This is a continuous process observed as a monotonic variation of the EPR spectral parameters and the unit cell dimensions. EPR spectra show that very weak exchange coupling J(12) = 0.0030 cm(-1) operates between Cu(2+) ions within asymmetric units, corresponding to the general formula of the compound, as well as between equivalent Cu(2+) sites of different molecules, whereas the coupling is negligible between inequivalent sites. The intermolecular J(12) coupling is temperature-independent indicating that the whole asymmetric unit behaves as a magnetic unit (pseudodimer) in the whole temperature range.     

Determination of fungicides in wine by mixed-mode solid phase extraction and liquid chromatography coupled to tandem mass spectrometry

A novel procedure for the determination of nine selected fungicides (metalaxyl-M, azoxystrobin, myclobutanil, flusilazole, penconazole, tebuconazole, propiconazole, diniconazole and difenoconazole) in wine samples is presented. Sample enrichment and purification is simultaneously performed using mixed-mode, anion exchange and reversed-phase, OASIS MAX solid-phase extraction (SPE) cartridges. Analytes were determined by liquid chromatography coupled to tandem mass spectrometry using atmospheric pressure electrospray ionization (LC-ESI-MS/MS). Parameters affecting the chromatographic determination and the extraction-purification processes were thoroughly investigated. Under optimized conditions, 10 mL of wine were firstly diluted 1:1 with ultrapure water and then passed through the mixed-mode SPE cartridge at a flow of ca. 5 mLmin(-1). After a washing step with 5 mL of an aqueous NH(4)OH solution (5%, w:v), analytes were recovered with just 1 mL of methanol and injected in the LC-MS/MS system without any additional purification. The selective extraction process avoided significant changes in the ionization efficiency for red and white wine extracts in comparison with pure standards in methanol. Performance of the method was good in terms of precision (RSDs<11%) and accuracy (absolute recoveries>72%, determined against pure standards in methanol) reporting method LOQs in the range of 0.01-0.79 ngmL(-1) for target compounds, which are far below the EU maxima residue levels (MRLs) for fungicides in vinification grapes and wine. Several commercial wines from different geographic areas in Spain were analyzed. In most samples, metalaxyl-M and azoxystrobin were found at concentrations up to several ngmL(-1).