Automation of static and dynamic non-dispersive liquid phase microextraction. Part 2: Approaches based on impregnated membranes and porous supports

A critical overview on automation of modern liquid phase microextraction (LPME) approaches based on the liquid impregnation of porous sorbents and membranes is presented. It is the continuation of part 1, in which non-dispersive LPME techniques based on the use of the extraction phase (EP) in the form of drop, plug, film, or microflow have been surveyed.     

MnO2/polyaniline hybrid nanostructures on carbon cloth for supercapacitor electrodes

Journal of Solid State Electrochemistry - A facile two-step strategy is developed for synthesis of MnO2/polyaniline (PANI) hybrid nanostructures on carbon cloth (CC). Vertically aligned PANI...     

Resolving Electronic Transitions in Synthetic Fluorescent Protein Chromophores by Magnetic Circular Dichroism

The detailed electronic structures of fluorescent chromophores are important for their use in imaging of living cells. A series of green fluorescent protein chromophore derivatives is examined by magnetic circular dichroism (MCD) spectroscopy, which allows the resolution of more bands than plain absorption and fluorescence. Observed spectral patterns are rationalized with the aid of time‐dependent density functional theory (TDDFT) computations and the sum‐over‐state (SOS) formalism, which also reveals a significant dependence of MCD intensities on chromophore conformation. The combination of organic and theoretical chemistry with spectroscopic techniques also appears useful in the rational design of fluorescence labels and understanding of the chromophore's properties. For example, the absorption threshold can be heavily affected by substitution on the phenyl ring but not much on the five‐member ring, and methoxy groups can be used to further tune the electronic levels.     

Optimization of a pressurized liquid junction nanoelectrospray interface between CE and MS for reliable proteomic analysis

A pressurized liquid junction nanoelectrospray interface was designed and optimized for reliable on-line CE-MS coupling. The system was constructed as an integrated device for highly sensitive and selective analyses of proteins and peptides with the separation and spray capillaries fixed in a pressurized spray liquid reservoir equipped with the electrode for connection of the electrospray potential. The electrode chamber on the injection side of the separation capillary and the spray liquid reservoir were pneumatically connected by a Teflon tube filled with pressurized nitrogen. This arrangement provided precisely counterbalanced pressures at the inlet and outlet of the separation capillary. The pressure control system was driven by an electrically operated valve and maintained the optimum flow rate for the electrospray stability. All parts of the interface being in contact with the CEBGE, spray liquid and/or sample were made of glass or Teflon. The use of these materials minimized the electrospray chemical noise often caused by plastic softeners or material degradation. During optimization, the transfer of the separated zones between the separation and electrospray capillaries was monitored by UV absorbance and contactless conductivity detectors placed at the outlet of the separation capillary and inlet of the electrospray tip, respectively. This arrangement allowed independent monitoring of the effects of pressure, CE voltage and geometry of the liquid junction on the spreading and dilution of the separated zones after passage through the interface.     

Determination of 1-methylhistidine and 3-methylhistidine by capillary and chip electrophoresis with contactless conductivity detection

CE with capacitively coupled contactless detection (C4D) was used to determine 3-methylhistidine (3-MH) and 1-methylhistidine (1-MH). The C4D response to 3-MH was studied in a BGE consisting of 500 mM acetic acid and ammonia at varying concentration and the results were compared with the theory. Complete separation of a model mixture of 3-MH, 1-MH, and histidine (His) was attained in two optimized BGEs, one containing 500 mM HAc, 20 mM NH4OH, and 0.1 % m/v hydroxyethylcellulose (HEC), pH 3.4 (I) and the other consisting of 100 mM morpholinoethanesulfonic acid (MES), 25 mM LiOH, and 0.1 % m/v HEC, pH 5.5 (II). These optimized BGEs were tested in CE/C4D analyses of urine. Promising results were obtained for separation and determination of 3-MH, 1-MH, and His on a silicon microchip, using aluminum strips as the C4D electrodes; the three analytes were baseline-separated within less than 30 s with a separation channel effective length of 38 mm. The LOD were satisfactory and amounted to 26.4 microM for 3-MH and 18.3 microM for 1-MH.     

Mercury speciation by CE: a review

CE methods for the speciation of inorganic and organomercury compounds are reviewed. Sample preparation, separation conditions and detection modes are discussed. Efficient separation and sensitive determination of mercury species by CE typically involves complexation with various thiols, chromogenic and other chelating agents; however, some methods do not require complexation. Spectrophotometric detection based on UV-visible absorption is by far the most commonly used. Hyphenated techniques, such as CE/inductively coupled plasma (ICP)-MS, hydride generation coupled to ICP-MS or atomic fluorescence spectrometry and CE/atomic absorption spectrometry are gaining popularity due to their high sensitivity and selectivity. Last, but not least, the potential and applications of electrochemical methods for detection of separated mercury species are outlined.     

Density functional theory augmented with an empirical dispersion term. Interaction energies and geometries of 80 noncovalent complexes compared with ab initio quantum mechanics calculations

Standard density functional theory (DFT) is augmented with a damped empirical dispersion term. The damping function is optimized on a small, well balanced set of 22 van der Waals (vdW) complexes and verified on a validation set of 58 vdW complexes. Both sets contain biologically relevant molecules such as nucleic acid bases. Results are in remarkable agreement with reference high-level wave function data based on the CCSD(T) method. The geometries obtained by full gradient optimization are in very good agreement with the best available theoretical reference. In terms of the standard deviation and average errors, results including the empirical dispersion term are clearly superior to all pure density functionals investigated-B-LYP, B3-LYP, PBE, TPSS, TPSSh, and BH-LYP-and even surpass the MP2/cc-pVTZ method. The combination of empirical dispersion with the TPSS functional performs remarkably well. The most critical part of the empirical dispersion approach is the damping function. The damping parameters should be optimized for each density functional/basis set combination separately. To keep the method simple, we optimized mainly a single factor, s(R), scaling globally the vdW radii. For good results, a basis set of at least triple-zeta quality is required and diffuse functions are recommended, since the basis set superposition error seriously deteriorates the results. On average, the dispersion contribution to the interaction energy missing in the DFT functionals examined here is about 15 and 100% for the hydrogen-bonded and stacked complexes considered, respectively.     

Automated measurement of permeation and dissolution of propranolol HCl tablets using sequential injection analysis

Aim of this study was to automate sampling and quantification of the previously described apparatus for combined determination of dissolution and permeation through Caco-2 monolayer by means of sequential injection analysis (SIA). Native fluorescence of propranolol HCl in Krebs-Ringer buffer (KRB) was used for quantification. Sampling was done at three different locations within the apparatus at a high sampling frequency (approximately 60 h⁻¹). Injection volume delivered to the fluorescence detector was 50 μL for permeation monitoring and 25 μL for dissolution monitoring. Linear regression for 50 μL injection yielded a detection limit calculated as 0.04 μg mL⁻¹ of propranolol HCl in KRB (R² > 0.999). However, linearity for dissolution monitoring was not given for the complete range of concentrations and first order polynomial calibration was established (R² > 0.9999). To conclude, the SIA system was able to monitor simultaneously dissolution and permeation of the immediate release propranolol HCl tablets and the authors succeeded in automating the apparatus for combined measurement of dissolution and permeation. In addition, the obtained data was consistent with data obtained by manual sampling followed by HPLC analysis.     

Catalytic activity of iron hexacyanoosmate(II) towards hydrogen peroxide and nicotinamide adenine dinucleotide and its use in amperometric biosensors

Hydrogen peroxide and nicotinamide adenine dinucleotide (NADH) may be determined amperometrically using screen-printed electrodes chemically modified with iron(III) hexacyanoosmate(II) (Osmium purple) in flow injection analysis (FIA). The determination is based on the exploitation of catalytic currents resulting from the oxidation/reduction of the modifier. The performance of the sensor was characterized and optimized by controlling several operational parameters (applied potential, pH and flow rate of the phosphate buffer). Comparison has been made with analogous complexes of ruthenium (Ruthenium purple) and iron (Prussian blue). Taking into account the sensitivity and stability of corresponding sensors, the best results were obtained with the use of Osmium purple. The sensor exhibited a linear increase of the amperometric signal with the concentration of hydrogen peroxide in the range of 0.1-100 mg L⁻¹ with a detection limit (evaluated as 3σ) of 0.024 mg L⁻¹ with a R.S.D. 1.5% for 10 mg L⁻¹ H₂O₂ under optimized flow rate of 0.4 mL min⁻¹ in 0.1 M phosphate buffer carrier (pH 6) and a working potential of +0.15 V versus Ag/AgCl. Afterwards, a biological recognition element - either glucose oxidase or ethanol dehydrogenase - was incorporated to achieve a sensor facilitating the determination of glucose or ethanol, respectively. The glucose sensor gave linearity between current and concentration in the range from 1 to 250 mg L⁻¹ with a R.S.D. 2.4% for 100 mg L⁻¹ glucose, detection limit 0.02 mg L⁻¹ (3σ) and retained its original activity after 3 weeks when stored at 6 °C. Optimal parameters in the determination of ethanol were selected as: applied potential +0.45 V versus Ag/AgCl, flow rate 0.2 mL min⁻¹ in 0.1 M phosphate buffer carrier (pH 7). Different structural designs of the ethanol sensor were tested and linearity obtained was up to 1000 mg L⁻¹ with a maximum R.S.D. of 5.1%. Applications in food analysis were also examined.     

High-throughput quantification of lincomycin traces in fermentation broth of genetically modified Streptomyces spp. Comparison of ultra-performance liquid chromatography and high-performance liquid chromatography with UV detection

A new separation and quantification method using ultra-performance liquid chromatography (UPLC) with UV detection was developed for detection of lincomycin traces in fermentation broth of different Streptomyces spp. A similar high-performance liquid chromatography (HPLC) protocol was simultaneously developed for comparison purposes. Both methods were validated and showed a linear range of detector response for quantification of lincomycin in concentration from 3.125 to 1000.0 microgml(-1) with correlation coefficient 0.999 and recoveries ranging from 81.5 to 89.85% with precision < or =5%. Compared with the HPLC, the UPLC method offered high sample throughput and about 10 times lower consumption of solvents. The developed assays were used for determination of lincomycin production in genetically manipulated production strain Streptomyces lincolnensis and for determination of lincomycin production after heterologous expression of lincomycin biosynthetic gene cluster in non-producing strain Streptomyces coelicolor.