A simple, rapid and precise gas chromatographic method has been developed for the simultaneous determination of miconazole nitrate (MIZ) and metronidazole (MNZ) in tablets and ovules, using a capillary column AE.SE-54 (15 m × 0.53 mm, i.d.) and nitrogen as a carrier gas at a flow rate of 9 mL min(-1). The oven temperature was programmed at 140°C for 3 min, with a rise of 40°C min(-1) up to 180°C (held for 2 min) and then increased to a final temperature of 250°C. The injector and detector port temperatures were maintained at 260°C. Detection was carried out using flame ionization detector. Results of assay and recovery studies were statistically evaluated for its accuracy and precision. The retention times were about 3.50 and 12.90 min for MNZ and MIZ, respectively. Linearity ranges were 50.0-6030.0 and 62.5-2000.0 μg mL(-1) for MNZ and MIZ, with limit of detection values of 2.5 and 3.1 μg mL(-1), respectively. Correlation coefficients (R(2)) of the regression equations were greater than 0.999 in all cases. No interference from any components of pharmaceutical dosage forms or degradation products was observed. According to the validation results, the proposed method was found to be specific, accurate, precise and could be applied to the simultaneous quantitative analysis of MIZ and MNZ in tablets and ovules.

This paper describes the design and experimental application of an optical system to perform schlieren measurements in the curved geometry of the cylinder of an optically accessible internal combustion engine. Key features of the system are a pair of cylindrical positive meniscus lenses, which keep the beam collimated while passing through the unmodified, thick-walled optical cylinder, and a pulsed, high-power light-emitting diode with narrow spectral width. In combination with a high-speed CMOS camera, the system is used to visualize the fuel jet after injection of hydrogen fuel directly into the cylinder from a high-pressure injector. Residual aberrations, which limit the system's sensitivity, are characterized experimentally and are compared to the predictions of ray-tracing software.

Development of a simple and rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the quantification of diquaternary ammonium gemini surfactants, utilized as gene deliver agents, is required for the evaluation of their post transfection fate. The continued development of efficient and safe gene delivery agents will benefit directly from an understanding of their rate of uptake, metabolism and excretion. A method is reported that is specific for the quantification of twenty-nine individual diquaternary ammonium gemini surfactant molecules and was validated for N,N-bis(dimethylhexadecyl)-1,3-propane-diammonium dibromide (G16-3) within PAM212 cell lysate according to USFDA bioanalytical method validation guidelines. The 10min chromatographic separation procedure utilized an Agilent Zorbax CN column (100mm×2.1mm with 3μ particles) with LC-MS grade water and acetonitrile, both containing 0.3% (v:v) formic acid and 1mM triethylamine. Extraction of the gemini surfactant from PAM212 keratinocyte cell lysate was performed using octanol and 10μL aliquots were injected onto the column. The standard curve was linear from 0.30μg/mL to 220μg/mL (r(2)≥0.999) for G16-3 and precision and accuracy were within USFDA specified limits. G16-3 analyte was assessed as stable during storage in the auto-injector, bench-top, freeze-thaw cycling and long-term (60 days) storage at -20°C. Evaluation of the cellular uptake and fate of G16-3, during both the incubation and post incubation periods, has established the potential of the application of the LC-MS/MS quantification method for monitoring diquaternary ammonium gemini surfactants in transfection studies.

Preparative capillary gas chromatography is a powerful tool for separation and purification of compounds from any complex matrix, which can be used for compound specific radiocarbon analysis. However, the effect of preparative capillary gas chromatography parameters on the trapping efficiency is not well understood. Here we present a comprehensive study on optimization of parameters based on eleven reference compounds with different physicochemical properties. Under the optimum conditions, the trapping efficiencies of eleven compounds (including high boiling point n-hentriacontane and methyl lignocerate) are ca. 80% (60% to 89%). The isolation of target compounds from standard solution, plant and soil samples demonstrates that our optimized method is applicable for different classes of compounds including n-alkanes, fatty acid esters, long chain fatty alcohol esters, PAHs and steranes. By injecting 25 μL in large volume injection mode, over 100 μg, high purity (>90%) target compounds are harvested within 24 h. The recovery ranges of two real samples are ca. 70% (59.9% to 83.8%) and ca. 83% (77.2% to 88.5%). Compared to previous studies, our study makes significant improvement in the recovery of preparative capillary gas chromatography, which is important for its wide application in biogeochemistry, environmental sciences and archaeology. This article is protected by copyright. All rights reserved.

We measured the lattice and subband electronic temperatures of terahertz quantum cascade devices based on the optical phonon-scattering assisted active region scheme. While the electronic temperature of the injector state (j = 4) significantly increases by ΔT = T_e ⁴ - T_L ~40 K, in analogy with the reported values in resonant phonon scheme (ΔT ~70-110 K), both the laser levels (j = 2,3) remain much colder with respect to the latter (by a factor of 3-5) and share the same electronic temperature of the ground level (j = 1). The electronic population ratio n₂/n₁ shows that the optical phonon scattering efficiently depopulates the lower laser level (j = 2) up to an electronic temperature T_e ~180 K.

We demonstrate the generation of temporally clean few-cycle pulses at 2.1 μm by shortening of 6-optical-cycle pulses via cross-polarized wave (XPW) generation in BaF₂, CaF₂ and CVD-Diamond crystals. By combining spectra and single-shot third-order intensity cross-correlation traces in a novel Bayesian pulse retrieval technique, we measured pulse durations of 20 fs, corresponding to 2.8 optical cycles. Our results show that XPW generation in the infrared could provide a high-fidelity source of few-cycle pulses for strong-field physics applications. It could also serve as an injector for high-peak power ultrafast mid-IR wavelength parametric amplifiers.

In this work, we propose a piezoelectric droplet generator for injection of well-defined amounts of sample in capillary electrophoresis. We demonstrate stable, precise and drop-on-demand droplet formation for various solutions, with precise control of waveform driving piezoelectric crystal inside the ink-jet head. By tuning the waveform, we can also manipulate the droplet size and delivery frequency. This injector was used in sampling for capillary electrophoresis. As a state-of-the-art application, the analysis of theobromine, caffeine and theophiline using micellar electrokinetic chromatography was developed. The volume of sample (single droplet) analyzed in this experiment was 179pL (RSD=1.2%, n=10). The detection limits for caffeine, theobromine, and theophiline are 0.02, 0.08 and 0.06mML(-1), respectively. Compared with conventional methods, the combination of picoliter droplet dispenser with capillary electrophoresis allows precise and accurate sampling, as well as for reduced sample consumption, which will prove to be an efficient tool in quantitative separation and analysis.

Although hundreds of papers related to preparative gas chromatography (pGC) have been published since the late 1950s, the success of the GC technique has largely been associated with analytical instead of preparative purposes. Actually, pGC is an ideal alternative technique for the preparation of pure substances, especially volatile compounds. This paper reviews the papers (written in English) associated with pGC published over the period from the 1950s to the 2010s. For large scale preparation, large sample injection and vaporization, a high loading capacity column, a gas splitter at the end of the column and a special collecting device are fundamentally important for a pGC system. The primary components of pGC system, including injector, column, splitter, detector and collection traps, are briefly introduced. Furthermore, the applications of pGC in the separation and purification of volatile compounds from natural essential oils, in addition to the purification of isotopes, isomers and enantiomers are summarized.

Turn the volume down: Coupling a high-pressure electroosmotic pump (EOP) and a microfabricated chip-injector with a bare narrow capillary-hydrodynamic chromatographic system (BaNC-HDC), enables samples to be injected at low-picoliter volumes, analytes to be eluted at picoliters per minute, and a wide size range of DNA fragments to be resolved rapidly in free solution at the single-molecule level.

Compared to conventional bench-top instruments, microfluidic devices possess advantageous characteristics including great portability potential, reduced analysis time (minutes), and relatively inexpensive production, putting them on the forefront of modern analytical chemistry. Fabrication of these devices, however, often involves polymeric materials with less-than-ideal surface properties, specific instrumentation, and cumbersome fabrication procedures. In order to overcome such drawbacks, a new hybrid platform is proposed. The platform is centered on the use of 5 interconnecting microfluidic components that serve as the injector or reservoirs. These plastic units are interconnected using standard capillary tubing, enabling in-channel detection by a wide variety of standard techniques, including capacitively-coupled contactless conductivity detection (C(4)D). Due to the minimum impact on the separation efficiency, the plastic microfluidic components used for the experiments discussed herein were fabricated using an inexpensive engraving tool and standard Plexiglas. The presented approach (named 5(2)-platform) offers a previously unseen versatility: enabling the assembly of the platform within minutes using capillary tubing that differs in length, diameter, or material. The advantages of the proposed design are demonstrated by performing the analysis of inorganic cations by capillary electrophoresis on soil samples from the Atacama Desert.