An SPE column-teflon sleeve assembly for in-line retention during supercritical fluid extraction of analytes from biological matrices

An in-line collector assembly designed for use in supercritical fluid extraction (SFE) vessels is described. This assembly enables solutes extracted by supercritical fluids (SF) to be retained in-line on standard solid phase extraction (SPE) columns. The assembly consists of a standard 1 mL or 3 mL SPE column fitted into a specially fabricated Teflon© sleeve. The SPE column-Teflon sleeve assembly is inserted into the SFE vessel followed by the sample matrix. This unit forms a leak-tight seal with the vessel's end-cap up to pressures of 680 bar. The choice of sorbents used in the in-line SPE columns is dependent upon the properties of the solute in the supercritical state. After SFE is completed, the SPE column is removed and the solutes are recovered in 1–2 mL of the eluting solvent. No further clean-up is normally required prior to chromatographic analysis of the analyte. A comparison was made of recoveries by in-line and off-line (after SF decompression) techniques for the SFE of three anabolic steroids in fortified chicken liver. The HPLC chromatograms of the steroids from the off-line SPE columns were too complex for quantitation, because of coeluting artifacts, whereas chromatograms obtained from in-line SPE columns were free from UV-absorbing interferences and were easily quantified.     

Permutation Entropy-Based Interpretability of Convolutional Neural Network Models for Interictal EEG Discrimination of Subjects with Epileptic Seizures vs. Psychogenic Non-Epileptic Seizures

The differential diagnosis of epileptic seizures (ES) and psychogenic non-epileptic seizures (PNES) may be difficult, due to the lack of distinctive clinical features. The interictal electroencephalographic (EEG) signal may also be normal in patients with ES. Innovative diagnostic tools that exploit non-linear EEG analysis and deep learning (DL) could provide important support to physicians for clinical diagnosis. In this work, 18 patients with new-onset ES (12 males, 6 females) and 18 patients with video-recorded PNES (2 males, 16 females) with normal interictal EEG at visual inspection were enrolled. None of them was taking psychotropic drugs. A convolutional neural network (CNN) scheme using DL classification was designed to classify the two categories of subjects (ES vs. PNES). The proposed architecture performs an EEG time-frequency transformation and a classification step with a CNN. The CNN was able to classify the EEG recordings of subjects with ES vs. subjects with PNES with 94.4% accuracy. CNN provided high performance in the assigned binary classification when compared to standard learning algorithms (multi-layer perceptron, support vector machine, linear discriminant analysis and quadratic discriminant analysis). In order to interpret how the CNN achieved this performance, information theoretical analysis was carried out. Specifically, the permutation entropy (PE) of the feature maps was evaluated and compared in the two classes. The achieved results, although preliminary, encourage the use of these innovative techniques to support neurologists in early diagnoses.     

1H NMR investigation of ring mobility of 1,5-benzodiazepine-2,4-diones

The ring mobility of some 1,5-benzodiazepine-2,4-diones and 1,4-benzodiazepin-2-one has been investigated by the temperature dependence of their ¹H NMR spectra. The activation parameters have been obtained, and the influence of N-1 substitution on the ring mobility is discussed, taking into account previously reported data for similar compounds.     

The mechanism of selective purine C-nitration revealed: NMR studies demonstrate formation and radical rearrangement of an N7-nitramine intermediate

Modified purine derivatives are of great importance in biomedical sciences, and substitution reactions on the purine skeleton are intensively studied. In our laboratory, an efficient and selective purine C2-nitration reaction was developed using a mixture of tetrabutylammonium nitrate and trifluoroacetic anhydride. The resulting 2-nitro moiety appeared to be a versatile handle to introduce a variety of pharmacophores onto the purine skeleton. Since the mechanism of this selective purine C2-nitration reaction has remained unclear, we now present an extensive NMR study leading to its elucidation, using N9-Boc-protected 6-chloropurine as a model compound. Direct electrophilic aromatic nitration of the highly electron-deficient C2 position was excluded, and we demonstrate that this reaction occurs in a three-step process. Electrophilic attack by trifluoroacetyl nitrate on the purine N7 position results in a nitrammonium species that is trapped by a trifluoroacetate anion furnishing N7-nitramine intermediate 11. This intermediate was characterized at -50 degrees C by (1)H, (13)C, (15)N, and (19)F NMR. At T > -40 degrees C, the N7-nitramine intermediate undergoes a nitramine rearrangement, which generates a C2-nitro species that immediately eliminates TFA to give 2-nitro-6-chloro-9-Boc purine 10. The involvement of radicals during the nitramine rearrangement was unequivocally established by (15)N-CIDNP. Moreover, the emission signal observed for the rearranged product, 2-nitropurine 10, showed that it is primarily formed in an intermolecular process. A quantitative radical trapping experiment finally disclosed that 65-70% of the nitramine rearrangement takes place intermolecularly.     

UREAphos: supramolecular bidentate ligands for asymmetric hydrogenation

Supramolecular bidentate phosphite ligands are presented as a new class of ligands for rhodium catalysed asymmetric hydrogenation.     

Towards a monolithic optical cavity for atom detection and manipulation

We study a Fabry-Perot cavity formed from a ridge waveguide on a AlGaAs substrate. We experimentally determined the propagation losses in the waveguide at 780 nm, the wavelength of Rb atoms. We have also made a numerical and analytical estimate of the losses induced by the presence of the gap which would allow the interaction of cold atoms with the cavity field. We found that the intrinsic finesse of the gapped cavity can be on the order of F∼30, which, when one takes into account the losses due to mirror transmission, corresponds to a cooperativity parameter for our system C∼1.     

Determination of nicotine and cotinine in rat plasma by liquid chromatography-tandem mass spectrometry

A method was developed for the efficient determination of nicotine and cotinine in rat plasma samples originating from nicotine exposure studies. Nicotine and cotinine were extracted from plasma samples with dichloromethane and concentrated to minimum volume with nitrogen stream. The volatility of nicotine was prevented by the addition of hydrochloric acid to the organic solvent during evaporation. The samples were analysed using liquid chromatography with triple quadrupole mass spectrometry. For quantification, the deuterated internal standards were added and the most intensive MS-MS ion of the analyte and internal standards were monitored. For confirmatory analysis, two specific MS-MS ions, viz. m/z 132 and 106 for nicotine and m/z 80 and 98 for cotinine, were monitored and the ratios between the ions were calculated and compared with those of standards. The ratios have to be within the tolerances of the EU criteria. The limit of identification of the developed method was 1 microg/l. The repeatability ranged from 5 to 12% (R.S.D.) for nicotine and from 3 to 5% for cotinine at the concentration level of 1-60 microg/l (n = 4).