A note on strong conciseness in virtually nilpotent profinite groups

Archiv der Mathematik - A group word w is said to be strongly concise in a class $${\mathcal {C}}$$ of profinite groups if, for every group G in $${\mathcal {C}}$$ such that w takes less than...     

Revisitation of the phenylisothiocyanate‐derivatives procedure for amino acid determination by HPLC‐UV

A revisitation of the well known chromatographic procedure for the determination of amino acids as phenylthiocarbamyl derivatives (PTC) is performed. The method was developed for a microbore column that it is more appropriate to our later aims, the characterization of proteinaceous binders present in microsamples coming from the Cultural Heritage field. Several variables relating to chromatographic aspects were studied such as the pH and temperature of the mobile phase, buffer and modifier (triethylamine) concentrations in mobile phase and the stability of PTC‐derivatives in solution. The calibration function was studied in depth. To prevent the heteroscedastic behaviour that it is observed, we used the weighed least squares fitting as the best strategy among other normalizing transformations, such as square root and logarithmic functions. Finally, the proposed method showed results similar to the traditional method in terms of efficiency, runtime, LODs and other characteristics, but with two additional advantages: a lower mobile phase consumption and the possibility of working with a lower sample volume. The usefulness of proposed method is checked against easel painting samples of Pictorial Heritage.     

Electrolytically initiated polymerization of N-vinylcarbazole

Polymerization of N-vinylcarbazole was studied systematically using electroinitiation with several quaternary ammonium salts as electrolytes in methylene chloride solution. Polymer was obtained only when the following electrolytes were used: tetraethylammonium perchlorate, tetrabutylammonium perchlorate, and tetrabutylammonium fluoroborate. Polymeric products of molecular weight 10⁴–10⁵ were formed in the anodic compartment of a divided cell. IR and ¹³C-NMR spectra showed that the structures of the polymers were similar to those produced by conventional cationic polymerization, which suggests a similar mechanism for the resulting anodic product.     

An unusual reaction polymerization in nitric acid medium

We are investigating an unusual reaction that occurs when methyl methacrylate (MMA) is kept in contact with concentrated nitric acid¹ (65% HNO₃, sp. gr. 1.41). Polymer of high molecular weight is formed, showing about one unit of methacrylic acid (MAA) per unit of MMA, when equilibrium is reached. The reaction depends on the temperature, the molar ratio MMA:HNO₃, and the reaction time. Although we also found polymer at temperatures in the range 50–70°C,² in this paper we only report the results when the temperature was kept between 25 and 40°C. Methacrylic acid (MAA) was found to homopolymerize under those mild conditions; its behavior was investigated. Although we also observed that polymer is formed with sulfuric acid (96%) and that acrylic acid polymerizes with both nitric and sulfuric acid at 20–30°C, we are limiting this article to the observed polymerizing action of nitric acid on methyl methacrylate and on methacrylic acid. Work proceeds on this matter in this laboratory.     

Determination of amphetamine-type stimulants in oral fluid by solid-phase microextraction and gas chromatography-mass spectrometry

A method for the simultaneous identification and quantification of amphetamine (AMP), methamphetamine (MET), fenproporex (FEN), diethylpropion (DIE) and methylphenidate (MPH) in oral fluid collected with Quantisal? device has been developed and validated. Thereunto, in-matrix propylchloroformate derivatization followed by direct immersion solid-phase microextraction and gas chromatography-mass spectrometry were employed. Deuterium labeled AMP was used as internal standard for all the stimulants and analysis was performed using the selected ion monitoring mode. The detector response was linear for the studied drugs in the concentration range of 2-256 ng mL(-1) (neat oral fluid), except for FEN, whereas the linear range was 4-256 ng mL(-1). The detection limits were 0.5 ng mL(-1) (MET), 1 ng mL(-1) (MPH) and 2 ng mL(-1) (DIE, AMP, FEN), respectively. Accuracy of quality control samples remained within 98.2-111.9% of the target concentrations, while precision has not exceeded 15% of the relative standard deviation. Recoveries with Quantisal? device ranged from 77.2% to 112.1%. Also, the goodness-of-fit concerning the ordinary least squares model in the statistical inference of data has been tested through residual plotting and ANOVA. The validated method can be easily automated and then used for screening and confirmation of amphetamine-type stimulants in drivers' oral fluid.     

A new diacylglycerol from fresh olive pulp

The isolation from olive pulp of a diacylglycerol showing an oleic as well as an elenoic acid residue, the latter probably derived from a natural enzymatic oleuropein hydrolysis, is reported. The given structure is supported by 1H- and 13C-NMR data.     

Determination of boron with chromotropic acid by first-derivative synchronous spectrofluorimetry

Summary A method for the determination of traces of boron by first-derivative synchronous spectrofluorimetry is proposed. It is based on the formation of a fluorescent complex with chromotropic acid at pH 6.7. The constant wavelength difference chosen to optimize the determination is =_em–_ex=24 nm. The range of application is between 2.0 and 20.0 /l of boron, the detection limit 0.4 g/l and the relative standard deviation 3.2%. A study was made of the influence of several ions as potential interferents. The method has been satisfactorily applied to the determination of boron in plants, fertilizers and natural waters.