Determination of cefotaxime and desacetylcefotaxime in cerebrospinal fluid by solid-phase extraction and high-performance liquid chromatography

A microfluidic analytical system for the separation and detection of organic peroxides, based on a microchip capillary electrophoresis device with an integrated amperometric detector, was developed. The new microsystem relies on the reductive detection of both organic acid peroxides and hydroperoxides at -700 mV (vs. Ag wire/AgCl). Factors influencing the separation and detection processes were examined and optimized. The integrated microsystem offers rapid measurements (within 130 s) of these organic-peroxide compounds, down to micromolar levels. A highly stable response for repetitive injections (RSD 0.35-3.12%; n = 12) reflects the negligible electrode passivation. Such a "lab-on-a-chip" device should be attractive for on-site analysis of organic peroxides, as desired for environmental screening and industrial monitoring.     

π Groups in ion pair bonding: the structural effects of reduction on the olefinic bond as observed in the molecular structure of Δ9,9′-bifluorenyl bis(lithium tetramethylethylenediamine)

The reaction of 9,9′-bifluorene with n-butyllithium in the presence of tetramethylethylenediamine (TMEDA) results in the formation of Δ^9,9′-bifluorenyl bis-(lithium tetramethylethylenediamine). In the molecular structure of this material, which formally can be considered to be the dianion of the olefin Δ^9,9′-bifluorene, two TMEDALi groups are closely associated with the 9,9′ bond. The fluorenyl groups are twisted relative to each other by an angle of 48.0(5)°, as compared to 42° in the parent olefin. The 9,9′ bond length is increased from 1.39(2) Å in Δ^9,9′-bifluorene to 1.487(5)Å in the dianion.Single crystal X-ray diffraction techniques were used and resulted in a final discrepancy factor of R_w = 0.064 for 2426 observations. The crystal system is monoclinic (C2/c) with a = 10.814(3), b = 16.717(6) and c = 19.766(6) Å, β = 102.55(2)°; ?_obs = 1.10(3) g cm^?3; ?_calc = 1.095 g cm^?3 for four molecules per unit cell.     

Adsorption of thiourea on mercury in water + methanol mixtures

The adsorption of thiourea on mercury has been investigated by capacitance measurements in three water + methanol mixtures, having various mole fractions of methanol.The back integration method was employed to obtain the curves of surface charge densities at the mercury surface for different concentrations of thiourea in the solution.As a test of specific adsorption in the systems studied the Esin-Markov plots were used.     

A Laboratory Study of Heterogeneous Catalysis in Ultrahigh Vacuum

A surface science experiment has been developed that can be used in both the undergraduate and graduate curriculum. Students study the mechanism of carbon monoxide oxidation using a platinum foil catalyst, and they also get hands-on experience with ultrahigh vacuum equipment. Using temperature programmed desorption, students study the desorption of carbon monoxide and oxygen from platinum foil in vacuum. The study allows students to determine that the Langmuir-Hinshelwood reaction mechanism operates in this catalytic system.     

Speciation of chromium in mineral waters and salinas by solid-phase extraction and graphite furnace atomic absorption spectrometry

A simple GF-AAS method for speciation analysis of chromium in mineral waters and salinas was developed. Cr(VI) species were separated from Cr(III) by solid-phase extraction with APDC (ammonium pyrrolidinedithiocarbamate). The APDC complexes were formed in the sample solution under proper conditions, adsorbed on Diaion HP-2MG resin and the resin was separated from the sample. After elution with concentrated nitric acid Cr(VI) was determined by GF-AAS. Total chromium was determined by GF-AAS directly in the sample and Cr(III) concentration was calculated as the difference between those results.

The detection limit of the method defined as 3 s of background variation was 0.03 μg l⁻¹ for Cr(VI) and 0.3 μg l⁻¹ for total chromium. RSD for Cr(VI) determination at the concentration of 0.14 μg l⁻¹ was 9%, and for total chromium at the concentration of 5.6 μg l⁻¹ was 5%. The recovery of Cr(VI) was in the range of 94–100%, dependently on type of the sample.

The investigation of recovery of the spiked Cr(VI) showed that at concentration levels near 1 μg l⁻¹ and lower recovery may be reduced significantly even by pure reagents that seem to be free from any reductants.     

Calibration of somatic cell count in milk based on near-infrared spectroscopy

A PLS model for prediction of somatic cell count (SCC) based on near-infrared (NIR) spectra of unhomogenized milk is presented in the study. Samples of raw milk were collected from cows in the early lactation period (from 7th to 29th day after parturition). The NIR spectra were measured in the region 400–1100 nm. As reference method a fluoro-opto-electronic method was applied. Different preprocessing methods were investigated. The robust version of PLS regression was applied to handle outliers present in the dataset and the uninformative variable elimination–partial least squares (UVE–PLS) method was used to eliminate uninformative variables. The final model is acceptable for prediction of SCC in raw milk.     

Robust partial least squares model for prediction of green tea antioxidant capacity from chromatograms

In this paper a robust version of the partial least squares model (partial robust M-regression, PRM) was built to predict the total antioxidant capacity of green tea extracts. In order to construct a calibration model, chromatograms obtained by a fast high-performance liquid chromatographic method on a monolithic silica column were related with the total antioxidant capacity of green tea extracts as determined by the Trolox antioxidant capacity method. Since natural samples are the subject of the study, some outlying samples are present in the data, as shown in an earlier work. Therefore, to construct reliable calibration models, they were detected and removed prior to modeling. With the applied robust partial least squares approach, where a weighting scheme is embedded to down-weight the negative influence of outliers upon the model it is possible to construct a robust calibration model, without prior identification of outlying objects. It was shown that a robust model, allowing satisfactory prediction for test samples, can be used in controlling green tea antioxidant capacity based on their chromatograms. The constructed robust partial least squares model was shown to have virtually the same fit and predictive power as the classical partial least squares model when outlying samples were removed from the data.     

Chemometrics in analytical chemistry—part II: modeling,validation, and applications

Analytical and Bioanalytical Chemistry - The contribution of chemometrics to important stages throughout the entire analytical process such as experimental design, sampling, and explorative data...     

Rethinking Carbohydrate Synthesis: Stereoretentive Reactions of Anomeric Stannanes

In this Concept article, recent advances are highlighted in the synthesis and applications of anomeric nucleophiles, a class of carbohydrates in which the C1 carbon bears a carbon–metal bond. First, the advantages of exploiting the carboanionic reactivity of carbohydrates and the methods for the synthesis of mono- and oligosaccharide stannanes are discussed. Second, recent developments in the glycosyl cross-coupling method resulting in the transfer of anomeric configuration from C1 stannanes to C-aryl glycosides are reviewed. These highly stereoretentive processes are ideally suited for the preparation of carbohydrate-based therapeutics and were demonstrated in the synthesis of antidiabetic drugs. Next, the application of the glycosyl cross-coupling method to the preparation of Se-glycosides and to glycodiversification of small molecules and peptides are highlighted. These reactions proceed with exclusive anomeric control for a broad range of substrates and tolerate carbohydrates with free hydroxyl groups. Taken together, anomeric nucleophiles have emerged as powerful tools for the synthesis of oligosaccharides and glycoconjugates and their future applications will open new possibilities to incorporate saccharides into small molecules and biologics.     

<Superscript>47</Superscript>Sc production development by cyclotron irradiation of <Superscript>48</Superscript>Ca

The therapeutic radionuclide ⁴⁷Sc was produced through the ⁴⁸Ca(p,2n) channel on a proton beam accelerator. The obtained results show that the optimum proton energies are in the range of 24–17 MeV, giving the possibility to produce ⁴⁷Sc radionuclide containing 7.4% of ⁴⁸Sc. After activation, the powdery CaCO₃ target material was dissolved in HCl and scandium isotopes were isolated from the targets. The performed separation experiments indicate that, due to the simplicity of the operations and the chemical purity of the obtained ⁴⁷Sc the best separation process is when scandium radioisotopes are separated on the 0.2 µm filter.