Experimental verification of an equivalent circuit for the characterization of electrothermal micropumps: High pumping velocities induced by the external inductance at driving voltages below 5 V

Electrothermal micropumps (ETμPs) use local heating to create conductivity and permittivity gradients in the pump medium. In the presence of such gradients, an external AC electric field influences smeared spatial charges in the bulk of the medium. When there is also a symmetry break, the field‐charge interaction results in an effective volumetric force resulting in medium pumping. The advantages of the ETμP principle are the absence of moving parts, the opportunity to passivate all the pump structures, homogeneous pump‐channel cross‐sections, as well as force plateaus in broad frequency ranges. The ETμPs consisted of a DC‐heating element and AC field electrodes arranged in a 1000 μm × 250 μm × 60 μm (length × width × height) channel. They were processed as platinum structures on glass carriers. An equivalent‐circuit diagram allowed us to model the frequency‐dependent pumping velocities of passivated and nonpassivated ETμPs, which were measured at medium conductivities up to 1.0 S/m in the 300 kHz to 52 MHz frequency range. The temperature distributions within the pumps were controlled by thermochromic beads. Under resonance conditions, an additional inductance induced a tenfold pump‐velocity increase to more than 50 μm/s at driving voltages of 5 V_rms. A further miniaturization of the pumps is viewed as quite feasible.     

Correcting for Spectral Cross‐Talk in Dual‐Color Fluorescence Cross‐Correlation Spectroscopy

Dual‐color fluorescence cross‐correlation spectroscopy (dcFCCS) allows one to quantitatively assess the interactions of mobile molecules labeled with distinct fluorophores. The technique is widely applied to both reconstituted and live‐cell biological systems. A major drawback of dcFCCS is the risk of an artifactual false‐positive or overestimated cross‐correlation amplitude arising from spectral cross‐talk. Cross‐talk can be reduced or prevented by fast alternating excitation, but the technology is not easily implemented in standard commercial setups. An experimental strategy is devised that does not require specialized hardware and software for recognizing and correcting for cross‐talk in standard dcFCCS. The dependence of the cross‐talk on particle concentrations and brightnesses is quantitatively confirmed. Moreover, it is straightforward to quantitatively correct for cross‐talk using quickly accessible parameters, that is, the measured (apparent) fluorescence count rates and correlation amplitudes. Only the bleed‐through ratio needs to be determined in a calibration measurement. Finally, the limitations of cross‐talk correction and its influence on experimental error are explored.     

Redox‐Active Nickel in Carbon Nanotubes and Its Direct Determination

The presence of residual metal‐catalyst impurities in carbon nanotubes is responsible for their toxicity. It is important to differentiate between the total amount of impurities and the redox‐active (bioavailable) amount of such impurities because only the bioavailable impurities exhibit toxic effects. Herein, we report a simple and specific method for quantifying the amount of redox‐active Ni present in various commercial samples of CNTs. It is based on the electrochemical oxidation of Ni(OH)₂ that is formed in alkaline solutions when Ni impurities are opened to the surrounding environment. Metallic Ni impurities play an extremely active role in toxicological assays as well as in undesired catalytic processes, and thus a method to rapidly quantify the amount of redox‐active Ni is of great importance.     

Direct Time‐Domain Observation of Conformational Relaxation in Gas‐Phase Cold Collisions

Cooling molecules in the gas phase is important for precision spectroscopy, cold molecule physics, and physical chemistry. Measurements of conformational relaxation cross sections shed important light on potential energy surfaces and energy flow within a molecule. However, gas‐phase conformational cooling has not been previously observed directly. In this work, we directly observe conformational dynamics of 1,2‐propanediol in cold (6 K) collisions with atomic helium using microwave spectroscopy and buffer‐gas cooling. Precise knowledge and control of the collisional environment in the buffer‐gas allows us to measure the absolute collision cross‐section for conformational relaxation. Several conformers of 1,2‐propanediol are investigated and found to have relaxation cross‐sections with He ranging from σ=4.7(3.0)×10^?18 cm² to σ>5×10^?16 cm². Our method is applicable to a broad class of molecules and could be used to provide information about the potential energy surfaces of previously uninvestigated molecules.     

An Extra‐Large‐Pore Pure Silica Zeolite with 16×8×8‐Membered Ring Pore Channels Synthesized using an Aromatic Organic Directing Agent

Extra‐large‐pore zeolites for processing large molecules have long been sought after by both the academia and industry. However, the synthesis of these materials, particularly extra‐large‐pore pure silica zeolites, remains a big challenge. Herein we report the synthesis of a new extra‐large‐pore silica zeolite, designated NUD‐6, by using an easily synthesized aromatic organic cation as structure‐directing agent. NUD‐6 possesses an intersecting 16×8×8‐membered ring pore channel system constructed by four‐connected (Q⁴) and unusual three‐connected (Q³) silicon species. The organic cations in NUD‐6 can be removed in nitric acid to yield a porous material with high surface area and pore volume. The synthesis of NUD‐6 presents a feasible means to prepare extra‐large pore silica zeolites by using assembled aromatic organic cations as structure‐directing agents.     

Synthesis and characterization of polymer electrolytes based on cross‐linked phenoxy‐containing polyphosphazenes

A new method to prepare the polymer electrolytes for lithium‐ion batteries is proposed. The polymer electrolytes were prepared by reacting poly(phosphazene)s (MEEPP) having 2‐(2‐methoxyethoxy)ethoxy and 2‐(phenoxy)ethoxy units with 2,4,6‐tris[bis(methoxymethyl)amino]‐1,3,5‐triazine (CYMEL) as a cross‐linking agent. This method is simple and reliable for controlling the cross‐linking extent, thereby providing a straightforward way to produce a flexible polymer electrolyte membrane. The 6 mol % cross‐linked polymer electrolyte (ethylene oxide unit (EO)/Li = 24:1) exhibited a maximum ionic conductivity of 5.36 × 10^?5 S cm^?1 at 100 °C. The ⁷Li linewidths of solid‐state static NMR showed that the ionic conductivity was strongly related to polymer segment motion. Moreover, the electrochemical stability of the MEEPP polymer electrolytes increased with an increasing extent of cross‐linking, the highest oxidation voltage of which reached as high as 7.0 V. Moreover, phenoxy‐containing polyphosphazenes are very useful model polymers to study the relationship between the polymer flexibility; that is, the cross‐linking extent and the mobility of metal ions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 352–358     

A PDMS sheath flow cuvette for high‐sensitivity LIF measurements in CE

A simple method for producing a sheath flow cuvette in PDMS suitable for post‐column detection in CE is described. Two types of cuvette were investigated. In the first, the sheath flow channel had a round cross‐section of approximately 635 μm diameter, whereas the second cuvette had a 300×300 μm² square channel. Both cuvettes produced laminar flows that ensheathed the separation capillary's effluent allowing sensitive fluorescence measurements. The elasticity of the PDMS allowed the 300×300 μm² square sheath flow channel to expand uniformly and accommodate the larger 330–340 μm od round separation capillary, producing a self‐aligning cuvette with robust mechanical properties. With this cuvette, linear calibrations of over five orders of magnitude and 15–30 zmol fluorescein detection limits were obtained for 12 and 50 μm id capillaries.     

MSn,LC‐MS‐TOF and LC‐PDA studies for identification of new degradation impurities of bupropion

Three new degradation impurities of bupropion were characterized through high performance liquid chromatography coupled to photodiode array detection and to time‐of‐flight mass spectrometry. Bupropion was subjected to the ICH prescribed stress conditions. It degraded to seven impurities (I–VII) in alkaline hydrolytic conditions which were optimally resolved on an XTerra C₁₈ column (250 × 4.6 mm, 5 µm) with a ternary mobile phase comprising ammonium formate (20 mm , pH 4.0), methanol and acetonitrile (75:10:15, v/v). The degradation impurities (III–V and VII) were characterized on the basis of mass fragmentation pattern of drug, accurate mass spectral and photodiode array data of the drug and degradation impurities. Compound V was found to be a known degradation impurity [1‐hydroxy‐1‐(3‐chlorophenyl)propan‐2‐one], whereas III, IV and VII were characterized as 2‐hydroxy‐2‐(3′‐chlorophenyl)‐3,5,5‐trimethylmorpholine, (2,4,4‐trimethyl‐1,3‐oxazolidin‐2‐yl)(3‐chlorophenyl)‐methanone and 2‐(3′‐chlorophenyl)‐3,5,5‐trimethylmorphol‐2‐ene, respectively. Compound III was a known metabolite of the drug. This additional information on the degradation impurities can help in the development of a new stability‐indicating assay method to monitor the stability of the drug product during its shelf‐life as well as in development of a drug product with increased shelf‐life. Copyright © 2013 John Wiley & Sons, Ltd.     

Herba Ecliptae Protects against Hydroxyl Radical‐induced Damages to DNA and Mesenchymal Stem Cells via Antioxidant Mechanism

Herba Ecliptae (HE) is a typical Chinese herbal medicine used in China for 1500 years. In the study, HE was extracted by various solvents to prepare five HE extracts. They were observed to possess a protective effect against ×OH‐induced DNA damage, and scavenging effects on ×OH radical, ×O₂^? radical, DPPH×(1,1‐diphenyl‐2‐picrylhydrazyl) radical, and ABTS×⁺ (2,2′‐azino‐bis(3‐ethyl‐benzothiazoline‐6‐sulfonic acid) radical, and reduce Cu²⁺ ion. The contents of total phenolics and wedelolactone in five extracts were determined respectively using Folin‐Ciocalteu method and HPLC method. To identify which chemical component can be responsible for its effects, the correlation graphs between chemical contents and antioxidant abilities (1/IC₅₀ values) were plotted to calculate correlation coefficients (R values). Finally, MTT assay revealed that two HE extracts could effectively protect mesenchymal stem cells (MSCs) against ×OH‐induced damage at 3‐30 μg/mL. On the basis of mechanistic analysis, we concluded that: (i) HE can effectively protect against ×OH‐induced damages to DNA and MSCs, thereby HE may have a therapeutic potential in MSCs transplantation or prevention of many diseases; (ii) the effects can be mainly attributed to total phenolics (R = 0.678) especially wedelolactone (R = 0.618); (iii) they exert antioxidant action via hydrogen atom transfer (HAT) and sequential electron proton transfer (SEPT) mechanisms.     

EU‐12: A Small‐Pore,High‐Silica Zeolite Containing Sinusoidal Eight‐Ring Channels

Zeolite EU‐12, the framework structure of which has remained unsolved during the past 30 years, is synthesized at a specific SiO₂/Al₂O₃ ratio using choline as an organic structure‐directing agent, with both Na⁺ and Rb⁺ ions present. Synchrotron powder X‐ray diffraction and Rietveld analyses reveal that the EU‐12 structure has a two‐dimensional 8‐ring channel system. Among the two distinct 8‐ring (4.6×2.8 and 5.0×2.7 Å) channels along c axis, the smaller one interconnects with the sinusoidal 8‐ring (4.8×3.3 Å) channel along a axis. The other large one is simply linked up with the sinusoidal channel by sharing 8‐rings (4.8×2.6 Å) in the ac plane. The proton form of EU‐12 was found to show a considerably higher ethene selectivity in the low‐temperature dehydration of ethanol than H‐mordenite, the best catalyst for this reaction.     

EU‐12: A Small‐Pore,High‐Silica Zeolite Containing Sinusoidal Eight‐Ring Channels

Zeolite EU‐12, the framework structure of which has remained unsolved during the past 30 years, is synthesized at a specific SiO₂/Al₂O₃ ratio using choline as an organic structure‐directing agent, with both Na⁺ and Rb⁺ ions present. Synchrotron powder X‐ray diffraction and Rietveld analyses reveal that the EU‐12 structure has a two‐dimensional 8‐ring channel system. Among the two distinct 8‐ring (4.6×2.8 and 5.0×2.7 Å) channels along c axis, the smaller one interconnects with the sinusoidal 8‐ring (4.8×3.3 Å) channel along a axis. The other large one is simply linked up with the sinusoidal channel by sharing 8‐rings (4.8×2.6 Å) in the ac plane. The proton form of EU‐12 was found to show a considerably higher ethene selectivity in the low‐temperature dehydration of ethanol than H‐mordenite, the best catalyst for this reaction.     

Study of a Novel Bisnaphthalimidopropyl Polyamine as Electroactive Material for Perchlorate‐selective Potentiometric Sensors

In this work, the new polyamine bisnaphthalimidopropyl‐4,4’‐diaminodiphenylmethane is proposed as a new ionophore for perchlorate potentiometric sensors. The optimal formulation for the membrane comprised of 12 mmol kg^?1 of the ionophore, and 68 % (w/w) of 2‐nitrophenyl phenyl ether as plasticizer and 31 % (w/w) of high molecular weight PVC. The sensors were soaked in water for a week to allow leakage of anionic impurities and for one day in a perchlorate solution (10^?4 mol L^?1) to improve reproducibility due to its first usage. The stability constant for the ionophore‐perchlorate association in the membrane, log β_IL1=3.18±0.04, ensured a performance characterized by the slope of 54.1 (±0.7) mV dec^?1 to perchlorate solutions with concentrations between 1.24×10^?7 and 1.00×10^?3 mol L^?1. The sensors are insensitive to pH between 3.5 to 11.0, they have a practical detection limit of 7.66 (±0.42) ×10^?8 mol L^?1 and a response time below 60 s for solutions with perchlorate concentrations above 5×10^?6 mol L^?1. The accuracy of the results was confirmed by the analysis of the contaminant in a certified reference water sample.     

ToF‐SIMS observation of PTFE surfaces modified by α‐particle irradiation

The surface structure of polytetrafluoroethylene (PTFE) upon α‐particle irradiation has been investigated at doses in the range of 1 × 10⁷ to 1 × 10¹¹ Rad and compared with the surface structure of the unirradiated polymer. Both neat and 25% fiberglass content PTFE were studied. The samples, maintained at nominal room temperature, were irradiated in vacuum by 5.5 MeV ⁴He²⁺ ions generated in a tandem accelerator beam line. Static time‐of‐flight SIMS (ToF‐SIMS) was employed to probe chemical changes at the surface as a function of the irradiation level. In general, the data are indicative of increased cross‐linking at α‐doses less than 1 × 10⁹ Rad, followed by increased fragmentation and unsaturation at α‐doses greater than 1 × 10⁹ Rad. Throughout the irradiation regime, scission is a constant factor promoting cross‐linking, branching, and unsaturation. However, at α‐doses greater than 1 × 10¹⁰ Rad, extreme structural degradation of the polymer becomes evident and is accompanied by conversion to oxygen‐functionalized and aliphatic compounds. Thus, for PTFE in an α‐particle field, an upper exposure limit of ～10¹⁰ Rad is essential for nominal retention of molecular structure. Finally, a quantitative relationship between α‐dose and characteristic fragment ion intensity is developed. Copyright © 2005 John Wiley & Sons, Ltd.     

A Germanosilicate Structure with 11×11×12‐Ring Channels Solved by Electron Crystallography

Zeolites have been widely used in industry owing to their ordered micropores and stable frameworks. The pore sizes and shapes are the key parameters that affect the selectivity and efficiency in their applications in catalysis, sorption, and separation. Zeolites with pores defined by 10 and 12 TO₄ tetrahedra are often used for various catalytic processes. To optimize the performance of zeolites, it is extremely desirable to fine‐tune the pore sizes/shapes. The first germanosilicate zeolite with a three‐dimensional 11×11×12‐ring channel system, PKU‐16 (PKU, Peking University) is presented. Nanosized PKU‐16 was structurally characterized by the new three‐dimensional rotation electron diffraction (RED) technique. PKU‐16 is structurally related to the zeolite β polymorph C (BEC, 12×12×12‐ring channels) by rotating half of the four‐rings in double mtw units.     

Evaluation of piezoelectric PVDF polymers for use in space environments. II. Effects of atomic oxygen and vacuum UV exposure

The effects of atomic oxygen (AO) and vacuum UV radiation simulating low Earth orbit conditions on two commercially available piezoelectric polymer films, poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐TrFE), have been studied. Surface erosion and pattern development are significant for both polymers. Erosion yields were determined as 2.8 × 10^?24 cm³/atom for PVDF and 2.5 × 10^?24 cm³/atom for P(VDF‐TrFE). The piezoelectric properties of the residual material of both polymers were largely unchanged after exposure, although a slight shift in the Curie transition of the P(VDF‐TrFE) was observed. A lightly cross‐linked network was formed in the copolymer presumably because of penetrating vacuum ultraviolet (VUV) radiation, while the homopolymer remained uncross‐linked. These differences were attributed to varying degrees of crystallinity and potentially greater absorption, and hence damage, of VUV radiation in P(VDF‐TrFE) compared with PVDF. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2503–2513, 2005     

Enhanced Microchip Electrophoresis of Neurotransmitters on Glucose Oxidase Modified Poly(dimethylsiloxane) Microfluidic Devices

In this paper, glucose oxidase (GOx) was employed to construct a functional film on the poly(dimethylsiloxane) (PDMS) microfluidic channel surface and apply to perform electrophoresis coupled with in‐channel electrochemical detection. The film was formed by sequentially immobilizing poly(diallyldimethylammonium chloride) (PDDA) and GOx to the microfluidic channel surface via layer‐by‐layer (LBL) assembly. A group of neurotransmitters (5‐hydroxytryptamine, 5‐HT; dopamine, DA; epinephrine, EP; dobuamine, DBA) as a group of separation model was used to evaluate the effect of the functional PDMS microfluidic devices. Electroosmotic flow (EOF) in the modified PDMS microchannel was well suppressed compared with that in the native one. Experimental conditions were optimized in detail. As expected, these analytes were efficiently separated within 110 s in a 3.7 cm long separation channel and successfully detected at a single carbon fiber electrode. Good performances were attributed to the decreased EOF and the interactions of analytes with the immobilized GOx on the PDMS surface. The theoretical plate numbers were 2.19×10⁵, 1.89×10⁵, 1.76×10⁵, and 1.51×10⁵ N/m at the separation voltage of 1000 V with the detection limits of 1.6, 2.0, 2.5 and 6.8 μM (S/N=3) for DA, 5‐HT, EP and DBA, respectively. In addition, the modified PDMS channels had long‐term stability and excellent reproducibility.     

Systematic evaluation of matrix effect and cross‐talk‐free method for simultaneous determination of zolmitriptan and N‐desmethyl zolmitriptan in human plasma: a sensitive LC‐MS/MS method validation and its application to a clinical pharmacokinetic study

The objective of the present work was to carry out systematic evaluation to eliminate matrix effect owing to plasma phospholipids as observed during sample preparation and to develop a cross‐talk‐free sensitive, selective and rapid bioanalytical method for the simultaneous determination of zolmitriptan (ZT) and N‐desmethyl zolmitriptan (DZT) in human plasma by liquid chromatography–tandem mass spectrometry using naratriptan as internal standard (IS). The analytes and IS were quantitatively extracted from 200 μL human plasma by solid phase extraction. No cross‐talk was found between ZT and DZT having identical product ions. Quantitation was performed on a triple quadrupole mass spectrometer employing electrospray ionization technique, operating in multiple reaction monitoring and positive ion mode. The total chromatographic run time was 2.5 min. The method was fully validated for sensitivity, selectivity, specificity, linearity, accuracy, precision, recovery, matrix effect, dilution integrity and stability studies. The method was validated over a dynamic concentration range of 0.1–15 ng/mL for ZT and DZT. The method was successfully applied to a bioequivalence study of 2.5 mg ZT tablet formulation in 18 healthy Indian male subjects under fasting conditions. Assay reproducibility was assessed by reanalysis of 62 incurred samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification of Impurities in 5-Aminolevulinic Acid by Two-Dimensional Column-Switching Liquid Chromatography Coupled with Linear Ion Trap Mass Spectrometry

Identification of impurities in 5-aminolevulinic acid (ALA) by mass spectrometry is difficult, because MS-incompatible mobile phases, such as phosphate buffers or ion-pair reagents, need to be used to separate the major component from impurities. In this study, the unknown impurities in ALA have been identified by two-dimensional (2D) column-switching high-performance liquid chromatography (HPLC) coupled with linear ion trap mass spectrometry (LIT MS). The first-dimensional analytical column was a Gemini C18 (150 mm × 4.6 mm, 5 μm) with a non-volatile salt mobile phase at a flow rate of 1.0 mL min⁻¹, and the second-dimensional analytical column was a ZORBAX SB C8 (150 mm × 4.6 mm, 3.5 μm) with a volatile salt mobile phase at a flow rate of 1.0 mL min⁻¹. The detection wavelength was 205 nm. Mass spectra were acquired with an ESI source, in both positive and negative ion modes. Six impurities were identified by their MS² and MS³ fragments, and the mass fragmentation patterns and structural assignments of these impurities were studied. The results obtained by the two-dimensional column-switching method were further compared with those of the conventional one-dimensional normal-phase HPLC–MS using an amide column and an MS-compatible mobile phase for separation. The two-dimensional column-switching method described herein proved to be advantageous in terms of the number of impurities identified. The column-switching and online demineralization technique made the mobile phase conditions compatible with mass spectrometry. Thus, the method solves the problem of incompatibility between non-volatile salt mobile phases and mass spectrometry, making it worthy of popularization and application in impurity identification.

     

Performance of HPLC/MS microchips in isocratic and gradient elution modes

We analyzed the chromatographic performance of particle‐packed, all‐polyimide high‐performance liquid chromatography/mass spectrometry (HPLC/MS) microchips in terms of their hydraulic permeabilities and separation efficiency under isocratic and gradient elution conditions. The separation channels of the chips (with ca 50 µm × 75 µm trapezoidal cross‐section and a length of 43 mm) were slurry packed with either 3.5 or 5 µm spherical porous C18‐silica particles. A custom‐built holder enveloped the chip during packing to prevent channel deformation and delamination from high pressures. It is shown that the packing conditions significantly impact the packing density of the HPLC/MS chips, which determines their performance in both, isocratic and gradient elution modes. Even with steep solvent gradients, peak shape and chromatographic resolution for the densely packed HPLC/MS chips are much improved. Our data show that the analytical power of the HPLC/MS chip is limited by the quality of the chromatographic separation. Copyright © 2010 John Wiley & Sons, Ltd.