On the reactivity of benzidinesulfonic acids and their applications in analysis: Reaction of cupric salts with o-benzidinemonosulfonic acid in presence of alkali thiocyanate

In the present work a new method for the detection of coppcr(II) is described. It is based on the reaction of this ion with the alkali salts of o-benzidinemonosulfonic acid, alkali thiocyanate being present. The sensitivity of this test is $\text{1}\text{500,000}$ (l0^-5.7); it ia specific for the Cu⁺² ion and can also be used to distinguish quickly the above-mentioned acid from the benzidine o-o'-disulfonic and benzidine m-m' '-disulfonic acids. It is believed that the mechanism of the reaction can be explained by an oxidation process.     

HPLC-Electrochemical detection with graphite-poly (tetrafluoroethylene) electrode Determination of the fungicides thiram and disulfiram

The suitability of composite graphite-poly(tetrafluoroethylene) (Teflon) electrodes as amperometric indicator electrodes in HPLC detection is demonstrated. The determination of the fungicides thiram and disulfiram in the presence of ziram has been chosen as an analytical problem. The optimization of working conditions, such as the choice of the organic solvent used in the mobile phase as well as its percentage, the potential applied to the composite electrode, and the time elapsed between mixing the carbamates and the injection, has been accomplished by using the wall-jet flow-cell configuration. The effect of the acetonitrile percentage used in the mobile phase on the retention of thiram, disulfiram, ziram and phenol was evaluated. Resolution up to the baseline can be achieved with 45% acetonitrile. The sensitivity of the determination of thiram and disulfiram in the presence of a constant concentration of ziram is slightly better when using a wall-jet cell; however, the background current is higher, as well as the baseline noise and the time necessary to achieve stabilization of the baseline before the injection. Lower limits of detection for both fungicides, as well as a better repeatability, were obtained when using a thin-layer flow cell configuration. As an application, the determination of thiram in spiked apple samples, at a level of 0.5 mg thiram kg(-1) apple, has been carried out with a mean recovery of 97 +/- 3% for a significance level of 0.05.     

The kinetics of radical polymerization—XXVII. Investigation of the radical reactivity of 3,3′- and 4,4′-disubstituted azobenzenes in the polymerization of vinylacetate

A study was made on the inhibition by some 3,3′- and 4,4′-disubstituted azobenzenes of the polymerization of vinylacetate initiated by azoisobutyronitrile at 50°. The inhibitory effects of these substances can be attributed to their ability to engage in radical addition giving a less reactive hydrazyl type radical. The mechanism of the inhibition has been established by ESR and kinetic (stoichiometric) measurements. The value of k₅/k₂ (characteristic of the reactivity of an inhibitor) was determined for 9 substituents. The radical reactivity of the aromatic azo group was decreased by electron donor substituents and increased by electron acceptors. The substituent effect can be well interpreted by the Hammett equation; the value of the reaction constant was ? = +0.53.     

Peak distortion in the column liquid chromatographic determination of omeprazole dissolved in borax buffer.

Injection of a sample containing omeprazole dissolved in borax buffer (pH 9.2) into a reversed-phase liquid chromatographic system consisting of a mixture of acetonitrile and phosphate buffer (pH 7.6) as the mobile phase and a C18 surface-modified silica as the solid phase resulted under special conditions in split peaks of omeprazole. The degree of peak split and the retention time of omeprazole varied with the concentration of borax in the sample solution and the ionic strength of the mobile phase buffer as well as with the column used. Borax is eluted from the column in a broad zone starting from the void volume of the column. The retention is probably due to the presence of polyborate ions. The size of the zone varies with the concentration of borax in the sample injected. In the borax zone the pH is increased compared with the pH of the mobile phase, and when omeprazole (a weak acid) is co-eluting in the borax zone its retention is affected. In the front part and in the back part of the borax zone, pH gradients are formed, and these gradients can induce the peak splitting. When the dissolving medium is changed to a phosphate buffer or an ammonium buffer at pH 9 no peak distortion of omeprazole is observed.     

Effect of the specific activity of the tracer on rat luteinizing hormone radioimmunoassay

Rat luteinizing hormone /LH/ was labelled with¹²⁵I by the Chloramine T method.¹²⁵I-LH, used as tracer in radioimmunoassay, was separated from the labelling reaction mixture by gel filtration. By using the proper protein/radioiodine ratio in the labelling reaction mixture the specific activity of¹²⁵I-LH was adjusted to 2.5–20.5 MBq g^–1. The influence of the specific activity on the assay parameters as well as on the tracer stability was investigated.     

Alkaloids of the flora of Mongolia V. Turpelline — A new alkaloid fromAconitum turczaninowii

In the course of a further study of the alkaloids of the epigeal part of Aconitum turczaninowiia new alkaloid has been isolated, which has been named turpelline. A structure for turpelline has been proposed on the basis of a study of its IR, mass, PMR, ¹³ C NMR, and 2D COSY spectra.     

Characterisation of Tokaj wines based on free amino acids and biogenic amines using ion-exchange chromatography

Summary Tokaj wines (Szamorodni and Aszu wines) of Hungarian origin were investigated on the basis of free amino acids and biogenic amines. The separation and determination of these compounds was performed by an amino acid analyser equipped with an ion-exchange resin column. The total amount of free amino acids and biogenic amines was higher in Aszu wines than in Szamorodni wines. The main amino acids were proline and arginine, while the major biogenic amines were tyramine and putrescine. The free amino acid and biogenic amine content of Aszu wines depended on the vineyards the wines originated from. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Natural radioactivity of building materials

Experiments were designed to measure trace uranium concentration and the rate of radon exhalation from masonry structural materials, both bare and surface finished and coated. LR115 cellulose nitrate track detectors were used to record the alpha emission from structural material surface. Fission track, neutron activation and fluorometric analysis methods were used to determine the uranium content. Most types of paints studied will reduce alpha contribution and radon emanation from building materials.     

A fluorimetric study of pindolol and its complexes with cyclodextrins

Spectrofluorimetric characteristics of pindolol have been investigated with the aim of using this technique for analytical determinations. Other monosubstituted indole derivatives, 4-methoxy and 5-methoxyindole, have been also studied for comparative purposes. Corrected excitation and emission wavelengths in different solvents are reported and the effect of solvent on the Stokes shifts of these compounds has been analysed using the Lippert equation. In addition, the Stokes shift of pindolol has been determined in dioxan-water solvent mixtures and the presence of specific solvent effects is discussed. The fluorescence of pindolol is pH dependent, the quantum yields determined in water are lower than those in other solvents. With respect to the sensitivity, it has been found that the detection limits in aqueous solutions are improved in the presence of beta and methyl-beta-cyclodextrin. Finally, a fluorimetric analysis of the interaction between pindolol and different cyclodextrins has been carried out in order to determine the apparent stability constants of the complexes and the thermodynamic parameters associated to complexation.     

Thermal rearrangements of 2-vinylcyclopropylidene to cyclopentadiene and vinylallene: a theoretical investigation

In an attempt to clarify the favored rearrangement reaction of vinylcyclopropylidenes, the prototype thermal rearrangements of singlet 2-vinylcyclopropylidene (1) leading to 1,3cyclopentadiene (2) and 1,2,4-pentatriene (vinylallene) (3) were investigated by means of ab initio quantum-mechanical electronic-structure calculations. The B3LYP functional with the 6-31G(d) basis set was employed for geometry optimization of the equilibrium and transition-state structures relevant to the two reaction pathways and for computing their harmonic vibrational frequencies. Final energies were evaluated by single-point calculations at the CCSD(T) level of theory with the 6-311 + G(3df,2p) basis set. The rearrangement of s-cis 1 to 2 is found to occur by a three-step pathway. The first step involves the formation of a nonclassical carbene (5), which is an internal pi complex between the pi molecular orbital of the double bond and the empty p atomic orbital of the carbene carbon. In the second step, the nonplanar five-membered ring geometry of 5 flattens to reach the planar structure of 3-cyclopentenylidene (4). The last step is the 1,2-migration of a alpha-hydrogen atom to the carbene center in 4. The rate-determining step for the rearrangement of s-cis 1 to 2 is the formation of 5, with a predicted global deltaG++(220 K) of only 0.6 kcalmol(-1). The rearrangement of s-trans 1 to 2 requires an initial conversion of s-trans 1 to the s-cis conformer, with a predicted deltaG++(220 K) of 1.8 kcalmol(-1). The transition structure for the ring-opening of s-trans 1 into s-trans 3 (deltaG++(220 K)=4.7 kcalmol(-1)) is more energetic than that for the ring-opening of s-cis 1 into s-cis 3 (deltaG++(220 K)=2.5 kcalmol(-2)) due to larger repulsive nonbonded H...H interactions in the former transition structure. On the basis of these results, it is suggested that if the reaction of 1,1-dibromo-2-vinylcyclopropane with methyllithium at -78 degrees C leads to the initial formation of carbene 1, then the reaction should yield 2 as the main product together with small amounts of 3. This theoretical prediction nicely agrees with experimental findings.