Sensitive gas analysis system on a microchip and application for on-site monitoring of NH3 in a clean room

A portable, highly sensitive, and continuous ammonia gas monitoring system was developed with a microfluidic chip. The system consists of a main unit, a gas pumping unit, and a computer which serves as an operation console. The size of the system is 45 cm width × 30 cm depth × 30 cm height, and the portable system was realized. A highly efficient and stable extraction method was developed by utilizing an annular gas/liquid laminar flow. In addition, a stable gas/liquid separation method with a PTFE membrane was developed by arranging a fluidic network in three dimensions to achieve almost zero dead volume at the gas/liquid extraction part. The extraction rate was almost 100% with a liquid flow rate of 3.5 μL/min and a gas flow rate of 100 mL/min (contact time of ~15 ms), and the concentration factor was 200 times by calculating the NH(3) concentration (w/w unit) in the gas and liquid phases. Stable phase separation and detection was sustained for more than 3 weeks in an automated operation, which was sufficient for the monitoring application. The lower limit of detection calculated based on a signal-to-noise ratio of 3 was 84 ppt, which showed good detectability for NH(3) analysis. We believe that our system is a very powerful tool for gas analysis due to the advantages of portable size, high sensitivity, and continuous monitoring, and it is particularly useful in the semiconductor field.     

Flow injection analysis and real-time detection of RNA bases by surface-enhanced Raman spectroscopy.

Surface-enhanced Raman scattering (SERS) spectroscopy has been successfully interfaced with a flow injection analysis system to detect RNA bases in real time. Four of the major base components of RNA, uracil, cytosine, adenine, and guanine, were introduced into the flow injection system and were mixed with a Ag sol prior to SERS measurements. Several experimental parameters including pH, temperature, flow rate, and tubing materials were examined, and their impact on the SERS spectra is presented here. The feasibility of interfacing flow injection based SERS detection methods with liquid or high-performance liquid chromatography for the detection of individual components in a complex mixture is also assessed.     

Flow injection analysis in a microfluidic format

A microfluidic flow injection analysis system has been designed and evaluated. The system incorporates within a single two-layer poly(dimethylsiloxane) monolith multiple pneumatically driven peristaltic pumps, an injection loop, a mixing column, and a transparent window for fluorescence detection. Central to this device is an injection system that mimics the operation of a standard six-port, two-way valve used in conventional liquid chromatography and flow injection experiments. Analyte and carrier solutions continuously flow through this injection system allowing for measurements and sample changes to be performed rapidly and simultaneously. Injection volumes of 1.25 nL generated peak area reproducibility of better than 3% relative standard deviation. The flow injection device was evaluated with fluorescent dyes and demonstrated a detection limit of 400 zmol for fluorescein. A rudimentary sample selection system allowed calibration curves to be rapidly produced, often in less than 10 min. The hydrolysis of fluorescein diphosphate by alkaline phosphatase demonstrates that chemical assays can be carried out with this device in a manner characterized by short analysis times and low sample consumption.     

Hydrodynamic study of ion transfer at the liquid/liquid interface: the channel flow cell

A hydrodynamic system based on the channel flow cell for voltammetric detection of ions at the liquid/liquid interface is reported. The current response for tetraethylammonium ion transfer across a membrane-supported liquid/liquid interface is shown to be consistent with existing theory for both the flow rate and voltage scan rate dependence of such processes, with no calibration factors or other adjustable parameters required. The analytical utility of such a device is discussed with specific regard to in situ measurements in flow systems.     

A high-efficiency cross-flow micronebulizer interface for capillary electrophoresis and inductively coupled plasma mass spectrometry.

A pneumatic nebulizer interface for capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICPMS) is reported. The interface is constructed using a high-efficiency cross-flow micronebulizer (HECFMN) and has the following features. (1) Makeup solutions can be fed to the interface by nebulizer self-aspiration and liquid gravity pressurization. (2) The liquid dead volume of the interface is approximately 65 nL, much smaller than those (200-2500 nL) reported for other interfaces. (3) The interface can be stably operated at a liquid flow rate down to 5 microL/min with a high analyte transport efficiency up to 95% to the plasma and (4) does not induce noticeable laminar flow in the CE capillary at typical nebulizer gas flow rates of 0.8-1.2 L/min. Because of these features, baseline resolution of 10 lanthanides with a CE-ICPMS system using the HECFMN interface is achieved, and detection limits and peak asymmetry are 0.05-1 microg/L and 0.93-1.23, respectively, improved significantly over those reported previously for a CE-ICPMS system using a high-efficiency nebulizer interface. Peak precision for the 10 lanthanides is in the range of 6.2-12.3% RSD (N = 5). Peak widths are from 9.1 s for 139La to 17.9 s for 175Lu. The effects of nebulizer gas flow rate, makeup solution flow rate, and spray chamber volume on CE-ICPMS signal intensity and separation are also evaluated for the HECFMN interface by the separation of Cr3+ and Cr2O7(2-).     

Photovoltaic–Pyroelectric Coupled Effect Induced Electricity for Self‐Powered Photodetector System

Ferroelectric materials have demonstrated novel photovoltaic effect to scavenge solar energy. However, most of the ferroelectric materials with wide bandgaps (2.7–4 eV) suffer from low power conversion efficiency of less than 0.5% due to absorbing only 8–20% of solar spectrum. Instead of harvesting solar energy, these ferroelectric materials can be well suited for photodetector applications, especially for sensing near‐UV irradiations. Here, a ferroelectric BaTiO₃ film‐based photodetector is demonstrated that can be operated without using any external power source and a fast sensing of 405 nm light illumination is enabled. As compared with photovoltaic effect, both the responsivity and the specific detectivity of the photodetector can be dramatically enhanced by larger than 260% due to the light‐induced photovoltaic–pyroelectric coupled effect. A self‐powered photodetector array system can be utilized to achieve spatially resolved light intensity detection by recording the output voltage signals as a mapping figure.     

Quantitative RP-HPLC Determination of Some Aldehydes and Hydroxyaldehydes as Their 2,4-Dinitrophenylhydrazone Derivatives

A high-performance liquid chromatographic (HPLC) method is described for the quantitative determination of some aliphatic aldehydes and β-hydroxyaldehydes as their 2,4-dinitrophenylhydrazone derivatives. A method is described for the preparation of derivatives for those β-hydroxyaldehydes where no reference compounds of known purity are available. The detection limit of the method was 4.3-21.0 μg/L, depending on the aldehyde.     

Evanescent-wave cavity ring-down spectroscopy for enhanced detection of surface binding under flow injection analysis conditions

The feasibility of liquid-phase evanescent-wave cavity ring-down spectroscopy (EW-CRDS) for surface-binding studies under flow-injection analysis (FIA) conditions is demonstrated. The EW-CRDS setup consists of an anti-reflection coated Dove prism inside a linear cavity (with standard or super-polishing of the total internal reflective (TIR) surface). A teflon spacer with an elliptical hole clamped on this surface acts as a 20 muL sized flow cell. The baseline noise of this system is of the order of 10(-4) absorbance units; the baseline remains stable over a prolonged time and the prism surface does not become contaminated during repeated injections of the reversibly adsorbing test dyes Crystal Violet (CV) and Direct Red 10 (DR10). At typical FIA or liquid chromatography (LC) flow rates, the system has sufficient specificity to discriminate between species with different surface affinities. For CV a much stronger decrease in ring-down time is observed than calculated based on its bulk concentration and the effective depth probed by the evanescent wave, indicating binding of this positively charged dye to the negatively charged prism surface. The amount of adsorption can be influenced by adjusting the flow rate or the eluent composition. At a flow rate of 0.5 mL/min, an enrichment factor of 60 was calculated for CV; for the poorly adsorbing dye DR10 it is 5. Super-polishing of the already polished TIR surface works counter-productively. The adsorbing dye Crystal Violet has a detection limit of 3 muM for the standard polished surface; less binding occurs on the super-polished surface and the detection limit is 5 muM. Possible applications of EW-CRDS for studying surface binding or the development of bio-assays are discussed.     

Selective Surface Enhanced Raman Scattering for Quantitative Detection of Lung Cancer Biomarkers in Superparticle@MOF Structure

Surface enhanced Raman scattering (SERS) is a trace detection technique that extends even to single molecule detection. Its potential application to the noninvasive recognition of lung malignancies by detecting volatile organic compounds (VOCs) that serve as biomarkers would be a breakthrough in early cancer diagnostics. This application, however, is currently limited by two main factors: (1) most VOC biomarkers exhibit only weak Raman scattering; and (2) the high mobility of gaseous molecules results in a low adsorptivity on solid substrates. To enhance the adsorption of gaseous molecules, a ZIF‐8 layer is coated onto a self‐assembly of gold superparticles (GSPs) in order to slow the flow rate of gaseous biomarkers and depress the exponential decay of the electromagnetic field around the GSP surfaces. Gaseous aldehydes that are released as a result of tumor‐specific tissue composition and metabolism, thereby acting as indicators of lung cancer, are guided onto SERS‐active GSPs substrates through a ZIF‐8 channel. Through a Schiff base reaction with 4‐aminothiophenol pregrafted onto gold GSPs, gaseous aldehydes are captured with a 10 ppb limit of detection, demonstrating tremendous prospects for in vitro diagnoses of early stage lung cancer.     

Miniaturized cavity ring-down detection in a liquid flow cell

A novel method for applying cavity ring-down spectroscopy in the liquid phase, compatible with LC analyses, is presented. The core of the setup is a home-built cavity ring-down flow cell (cell volume 12 microL) that is constructed using a silicon rubber spacer, which is clamped leak-tight between two high-reflectivity mirrors. The mirrors are in direct contact with the liquid flow, which provides for a small path length and short ring-down times. Inside the cavity there are no windows, reflection losses, or Brewster angles to be considered. Due to the small size of the presented cavity geometry, the setup can be implemented in conventional-size LC apparatuses. With a flow injection setup, a detection limit of 2.5 nM was obtained for Crystal Violet in ethanol, and the linear dynamic range of the system is at least 2 orders of magnitude. The method has the potential to become a powerful alternative for commercial LC UV/visible absorbance detectors.     

Electric time-domain reflectometry sensor for online flow sensing in liquid composite molding processing

This paper describes the development of a new sensor type for resin flow detection in liquid composite molding (LCM) processing. The sensor can be applied in any LCM process where lineal and high-resolution flow front detection is required, i.e. during prototyping or as a feedback sensor during flow front control. The operating principle of the embedded sensor is based on electrical time domain reflectometry (E-TDR). The system analyzes changes in the transmission line response during wet-out of the preform. The flat band transmission line, which is interrogated by E-TDR changes its dielectric properties when the resin is on or near the sensor resulting in reflection of the electrical signal. The signal is evaluated in the time-domain by mapping the areas of resin on the sensor. The study illustrates an analytical model to predict the TDR response for different resin systems, validates the accuracy and resolution of the system in a lab-scale set-up and implements the sensor in several different injection scenarios.     

光伏并网式家用空调系统性能的实验研究

针对目前的家用空调系统,本文设计了一种以太阳能光伏发电技术为基础,与国家电网并网,共同驱动空调工作的系统,称为光伏并网式家用空调系统。利用光伏发电技术,通过逆变器将太阳能提供的电力转变为220 V、50 Hz家用电源,实现与市电电网的并网,来共同驱动空调运行。利用焓差实验室,对光伏并网式家用空调系统在连接100 W、135 W和185 W不同功率太阳能电池板进行空调系统的性能实验。实验结果表明:光伏并网式空调系统能稳定驱动运行。在标准工况下,与常规家用空调系统相比,制冷模式下,光伏并网式空调系统的制冷功率分别减少52 W、78 W和104 W,能效比分别提高4.2%、5.5%和10.2%。制热模式下,光伏并网式空调系统的制热功率分别减少68 W、84 W和116 W,性能系数分别提高6.4%、8%和11%。这表明光伏并网式家用空调系统是可行的,还可以有效节能。     

基于改进遗传算法的光伏系统储能优化配置

为应对光伏发电随机性及波动性对电力系统造成的不利影响,可以从系统概率潮流角度分析光伏出力特征,进而研究储能的接入对于抑制该影响的可行方案.首先,建立概率潮流元件分布模型和储能选址定容模型,采用随机行走理论和拉丁超立方理论进行样本分析和排序;其次,以降低储能投资成本、降低支路有功越限概率和减少网络损耗作为优化目标函数并进...     

On-line liquid chromatography-accurate radioisotope counting coupled with a radioactivity detector and mass spectrometer for metabolite identification in drug discovery and development

A novel detection method combining on-line liquid chromatography-accurate radioisotope counting (LC-ARC, advanced stop flow controller) coupled with a radioactivity detector and mass spectrometer has been developed. One of the major benefits of this method is that this system enhances the sensitivity of radioisotope measurement for metabolite identification in drug metabolism studies. Another advantage to this system is the easy interface with the mass spectrometer, which allows acquisition of mass spectrometric data on-line. For purposes of evaluating this system, in vitro microsomal incubations with [3Hlpropranolol were conducted. On-line separation and identification of [3H]propranolol metabolites was achieved without intensive sample preparation, concentration, or fraction collection. Mass spectrometric analysis showed the presence of propranolol major metabolites formed by hydroxylation, correlating with previously published results. Further evaluations of this system also were conducted using two 14C compounds, which are herein labeled X and Y. As our results show, 14C peaks were detected down to 6 cpm, which is approximately 20 times more sensitive than commercially available flow through radioactivity detectors. The overall results suggest that the combination of LC-ARC with radioactivity detection and mass spectrometry has great potential as a powerful tool for improving the sensitivity of radioisotope measurement in metabolite identification studies during drug discovery and development.     

Chemical reaction interface mass spectrometry with high efficiency nebulization

A high efficiency nebulizer (HEN) coupled to a heated spray chamber and a membrane desolvator is used for liquid sample introduction in chemical reaction interface mass spectrometry (CRIMS). Compared to the conventional thermospray nebulizer operated at solvent flow rate of 1 mL/min, the HEN provides small droplets at lower flow rates (10-100 microL/min), improving the desolvation and analyte transport efficiency. As a result, the sensitivity for carbon detection by CRIMS is improved by a factor of 4. The new arrangement offers an easy-to-use and robust interface, facilitating the availability of a variety of liquid chromatographic techniques to the CRIMS. Separation and detection of labeled peptides in a mixture of unlabeled biopolymers is illustrated at a solvent flow rate of 45 microL/min as an example of new possibilities offered by the improved liquid introduction interface.     

Liquid-phase chemical and biochemical detection using fully integrated magnetically actuated complementary metal oxide semiconductor resonant cantilever sensor systems

A novel resonant cantilever sensor system for liquid-phase applications is presented. The monolithic system consists of an array of four electromagnetically actuated cantilevers with transistor-based readout, an analog feedback circuit, and a digital interface. The biochemical sensor chip with a size of 3 mm x 4.5 mm is fabricated in an industrial complementary metal oxide semiconductor (CMOS) process with subsequent CMOS-compatible micromachining. A package, which protects the electrical components and the associated circuitry against liquid exposure, allows for a stable operation of the resonant cantilevers in liquid environments. The device is operated at the fundamental cantilever resonance frequency of approximately 200 kHz in water with a frequency stability better than 3 Hz. The use of the integrated CMOS resonant cantilever system as a chemical sensor for the detection of volatile organic compounds in liquid environments is demonstrated. Low concentrations of toluene, xylenes, and ethylbenzene in deionized water have been detected by coating the cantilevers with chemically sensitive polymers. The liquid-phase detection of analyte concentrations in the single-ppm range has been achieved. Furthermore, the application of this sensor system to the label-free detection of biomarkers, such as tumor markers, is shown. By functionalizing the cantilevers with anti-prostate-specific antigen antibody (anti-PSA), the corresponding antigen (PSA) has been detected at concentration levels as low as 10 ng/mL in a sample fluid.     

Selective detection of volatile aromatic compounds using a compact laser ionization detector with fast gas chromatography

We report results for a new gas chromatography detector that is comparatively sensitive and far more selective for aromatic compounds than the traditional photoionization detector. The detection means is multiphoton ionization at atmospheric pressure. The ionization source in these experiments is a diode-pumped passively Q-switched microchip laser operating at 266 nm. Experiments were conducted with the detector interfaced to a fast gas chromatograph. For <20 s elution time, limits of detection were <1 pg for toluene, ethylbenzene, xylenes, and isopropylbenzene; the limit of detection for benzene is approximately 10 pg. Detector response was linear over 5 orders of magnitude, including these low levels. Negligible signals were observed for nonaromatic ketones, aldehydes, ethers, and cycloalkanes at levels as high as 0.1 microg (10 mg/L concentration). Detector efficiency after fast GC separation was 0.002% when using a detector cell with a radius of 1.1 cm and a purge gas flow of 500 mL/min. The advantages of this detector are further illustrated by the fast GC analysis of fuel samples.     

A novel method of determining the permittivity of liquids

A novel method to measure the permittivity of liquids is used in a microwave gauging system, developed for the detection of liquid levels in tanks. The system is described as a frequency stepped continuous wave (FSCW) radar for precision liquid level detection. Usually a radar system is only employed to find the surface of the liquid. With the microwave measurement system described here, one can detect a second level that may be the tank bottom or an impurity level, for example. To monitor the permittivity of the liquid with the same measurement system, a novel algorithm is derived. Measured uncertainties of ±0.2 mm have been achieved for the multilevel range detection performed in the frequency range from 2 to 3 GHz. From these measured data, the error of the calculated permittivity was about 2%. By using this technique to determine the permittivity of the liquid, it is possible to reduce the complexity of the measurement system     

Sample dispersion for segmented flow in microchannels with rectangular cross section

Hydrodynamic dispersion in microchannels can be significantly reduced by segmentation with a second immiscible phase. We address the effect of microchannel cross section on the dispersion of analytes in a segmented gas-liquid flow of alternating bubbles and liquid segments. Channels of square or nearly square cross section are considered. A significant fraction of the liquid surrounds the bubbles and wets the channel walls in the form of films or menisci. This stagnant fraction of the liquid remains when gas and liquid segments flow by, and it is connected to the liquid within the liquid segments by diffusion only and it effectively increases dispersion. We design and fabricate a microchip with integrated analyte injection and detection to investigate the effects of the influence of the stagnant liquid in segmented flow through square microchannels on the analyte bandwidth. The measured data and a corresponding model confirm the experimental trends and suggest operating conditions at which the unwanted effect of dispersion in segmented microchannel flow is minimized. Dispersion is least when the liquid flow rate is greater than the gas flow rate, and the optimum ratio of the two flow rates slightly increases with increasing bubble velocity.     

N-Methyl-4-hydrazino-7-nitrobenzofurazan as a New Reagent for Air Monitoring of Aldehydes and Ketones

The synthesis of N-methyl-4-hydrazino-7-nitrobenzofurazan (MNBDH) and its application as a new reagent for the determination of aldehydes and ketones are described. MNBDH reacts with carbonyl compounds in acidic media to the corresponding MNBD-hydrazones. In contrast to the established reagent 2,4-dinitrophenylhydrazine (DNPH), MNBDH is oxidized by both ozone and nitrogen dioxide quantitatively to only one product, N-methyl-4-amino-7-nitrobenzofurazan (MNBDA). This can easily be separated from the hydrazones of lower aldehydes by means of HPLC. Due to larger molar absorptivities and absorption maxima at wavelengths over 470 nm, selectivity is higher and limits of detection are lower for the new reagent compared to DNPH. MNBDH reacts slightly faster than DNPH with carbonyl compounds and significantly faster than other N-alkylated hydrazine reagents.