Polydimethylsiloxane permeability-based method for the continuous and specific detection of hydrogen sulfide

Hydrogen sulfide (H(2)S) is known to play a physiological role in processes as diverse as vasodilation, maintenance of vascular tone, neurotransmission, and immune response. The multitude of physiological functions in which H(2)S is involved warrants the development of useful methods for its detection. Here, we introduce a simple and continuous H(2)S detection method that exploits the relatively high polydimethylsiloxane (PDMS) permeability of H(2)S in comparison to other thiols typically encountered in the cellular milieu. In this method, 96-well inserts constructed of PDMS act as an H(2)S-permeable membrane, eliminating nonspecific thiol detection. This design also makes it possible to use virtually any available thiol-specific probe such as Ellman's reagent which was used here to detect H(2)S once it crossed the PDMS membrane. Utilizing this method, a detection limit of 9.2 ± 1.9 ppb(m) (parts per billion (by mole) or ~0.51 μM in 1.6 mL of buffer) free H(2)S (detected as solution sulfide) was achieved. In addition, the assay was used to determine K(M) and V(max) for natural substrates of cystathionine γ-lyase (CSE), the main enzyme responsible for H(2)S production in peripheral tissues. The K(M) and V(max) of CSE for cysteine were 3.79 ± 2.07 mM and 0.37 ± 0.02 nmol H(2)S/min, respectively. K(M) and V(max) for homocysteine were 6.90 ± 1.78 mM and 1.10 ± 0.19 nmol H(2)S/min, respectively. In addition, the assay was used to examine the potential for a direct interaction of H(2)S and NO. The levels of detected H(2)S decreased in the presence of NO under normoxia but not under anoxia indicating that H(2)S does not react with NO but with N(2)O(3) likely formed in the hydrophobic environment of PDMS.     

连续测氡仪测定空气中氡浓度方法探讨

在民用建筑工程室内环境中氡浓度的测定方法中,用连续测氡仪测定氡浓度是一种方便、快捷的方法,但在实际检测过程中,由于操作等原因,仪器的测量准确度较低。在标准氡室(HD-1型)里模拟实验用标准氡浓度,以RAD7连续测氡仪为例,探讨了取样测量时间、空气湿度对空气中氡浓度测量的准确性的影响。结果表明,在取样测量时间不低于30min、较低空气湿度(10%)条件下,用连续测氡仪测量空气中氡浓度可以获得满意的数据。     

A pulse amperometric sensor for the measurement of atmospheric hydrogen peroxide

Gaseous H(2)O(2) is sampled through a Nafion membrane diffusion scrubber while 1 mM HCl is maintained stationary in the scrubber. After a preselected preconcentration time (typically, 5-10 min), a valve is opened to allow the scrubber liquid to flow by gravity over an electrochemical H(2)O(2) sensor for a brief period. The miniature flow-over sensor consists of a Pt/Rh wire working electrode and a Pt wire counter electrode wound respectively on separate segments of a Nafion solid polymer electrolyte tubing supported on a Ag/AgCl wire reference electrode. A simple electronic interface and a personal computer are used to control and record the electrochemical measurement. The liquid phase detection limit for this sensor is ～30 nM H(2)O(2) in the anodic oxidation mode. For a 9 min gas sample preconcentration period, the LOD (S/N = 3 criterion) is 0.11 ppbv H(2)O(2)(g). Ambient H(2)O(2) data obtained with this instrument were in excellent agreement with those obtained by an established fluorometric technique in a blind intercomparison.     

Hybrid microfabricated device for field measurement of atmospheric sulfur dioxide

A miniaturized planar-membrane-based gas collector of 800 nL internal liquid volume was integrated with a microfabricated conductivity detector to measure atmospheric SO2. This device is operated with a dilute H2SO4/ H202/2-propanol absorber for a finite integration period (typically, 1.5 min) without liquid flow. During this period, sulfuric acid is formed from SO2 that diffuses into the liquid and accumulates therein. The increase in conductivity with ongoing sampling is measured. The absorber is then replaced with fresh solution, and the process starts anew. The most important factors that govern sensitivity and the detection limit are the choice of the membrane, the nature of the internal collector solution, and the thickness of the solution layer. A porous polypropylene membrane with some 2-propanol (IPA) incorporated in the internal solution was found to be the best combination. The sensitivity was inversely proportional to the solution layer thickness, and a layer thickness of 100 microm resulted in a practical device with good performance characteristics. Greater applied pressure on the gas phase relative to the liquid side also can improve device performance. The system is operated with 12 V DC and does not require a liquid pump. Under optimized conditions, the LOD is 0.7-1.0 ppbv for a sampling period of 1.5 min. The device was field-tested around Mt. Aso in Japan. Changes in ambient SO2 concentrations could be followed with good time resolution. The results are compared with data obtained by a collocated macroscale instrument.     

Speciation-capable field instrument for the measurement of arsenite and arsenate in water

Hydride generation to form arsine and in-line preconcentration of the arsine into an alkaline KMnO4 receiver followed by molybdenum blue (MB) colorimetric determination of the arsenate formed is proposed for the highly sensitive and separate measurement of total inorganic As and As(III). Reduction of As to AsH3 is carried out by NaBH4; when the reduction is carried out at pH 1, all the inorganic As is reduced to AsH3, and when carried out at pH 7, only As(III) is reduced. Reductions at the two different pH levels are carried out in two different arsine generators simultaneously using constant addition of NaBH4 with solenoid pumps. The AsH3 is collected by individual porous membrane diffusion scrubbers filled with a stationary solution of KMnO4, and the contents of the two scrubbers sequentially enter a flow analysis stream. MB is formed by merging with a ammonium molybdate-ascorbic acid reagent, passing through a heated reactor, and is then measured by a LED/photodiode-based absorbance detector. Robustness was confirmed for total As using three types of certified natural water samples. Speciation analysis data from well water samples analyzed by this method agree well with HPLC-ICPMS measurements in a different laboratory. The system has been successfully applied to field measurements of As(III) and As(V), where levels were significantly below 1 mug/L. For a 20-mL sample, the limits of detection (LODs) for this inexpensive instrument are 0.3 microg/L for both As(III) and total As. When an 80-mL sample is analyzed, LODs are 0.07 microg/L As(III) and 0.09 microg/L total As. The general approach should be applicable to many other analyte species of interest that can be isolated from the matrix by the formation of a suitable volatile compound that can be recaptured.     

Evaluation of small hydrogen sulfide concentrations in calibrating commercial gas analyzers for hydrogen sulfide

Conclusions Small concentrations (10^–5–10^–2 by volume) of hydrogen sulfide in gas mixtures can be analyzed by means of the photocolorimetric method based on the formation of molybdenum blue by the interaction of hydrogen sulfide with ammonium molybdate in an acidic medium.The optimum conditions for reducing molybdate by hydrogen chloride are provided by a content of 50 mg/ml of ammonium molybdate in the absorbing solution, a sulfuric solution with an acidity of 0.6 N, and a coloration ripening time of 15–20 min.     

Aerosol counterflow two-jets unit for continuous measurement of the soluble fraction of atmospheric aerosols

A new type of aerosol collector employing a liquid at laboratory temperature for continuous sampling of atmospheric particles is described. The collector operates on the principle of a Venturi scrubber. Sampled air flows at high linear velocity through two Venturi nozzles "atomizing" the liquid to form two jets of a polydisperse aerosol of fine droplets situated against each other. Counterflow jets of droplets collide, and within this process, the aerosol particles are captured into dispersed liquid. Under optimum conditions (air flow rate of 5 L/min and water flow rate of 2 mL/min), aerosol particles down to 0.3 microm in diameter are quantitatively collected in the collector into deionized water while the collection efficiency of smaller particles decreases. There is very little loss of fine aerosol within the aerosol counterflow two-jets unit (ACTJU). Coupling of the aerosol collector with an annular diffusion denuder located upstream of the collector ensures an artifact-free sampling of atmospheric aerosols. Operation of the ACTJU in combination with on-line detection devices allows in situ automated analysis of water-soluble aerosol species (e.g., NO2-, NO3-)with high time resolution (as high as 1 s). Under the optimum conditions, the limit of detection for particulate nitrite and nitrate is 28 and 77 ng/m(3), respectively. The instrument is sufficiently rugged for its application at routine monitoring of aerosol composition in the real time.     

Pulsed excitation source multiplexed fluorometry for the simultaneous measurement of multiple analytes. Continuous measurement of atmospheric hydrogen peroxide and methyl hydroperoxide

Presently, solid-state sources such as light-emitting diodes (LEDs) provide for intense, nearly monochromatic light. They are available over a broad range of emission wavelengths. Unlike incandescent and discharge lamps, LEDs can be turned on and off at high speeds. The resulting light pulses are highly reproducible. This allows the use of a single photomultiplier tube (PMT), often the most expensive component in a high-sensitivity measurement system, as a multiplexed detector with multiple, fiber-optic-coupled, fluorescence-detection cells excited by solid-state sources. A time resolution of 1 min is adequate in many continuous detection schemes. This enables multiple-channel single-detector multiplexed measurement without any loss of S/N. On the basis of this principle, we describe a new automated continuous instrument for the simultaneous measurement of atmospheric hydrogen peroxide and methyl hydroperoxide (MHP). A Nafion membrane diffusion scrubber (DS) is used with hematin-catalyzed oxidation of thiamine to thiochrome for the measurement of H2O2, and an expanded poly(tetrafluoroethylene) (ePTFE) DS is used with a H2O2 destruction catalyst and horseradish peroxidase-catalyzed oxidation of thiamine to thiochrome for the measurement of MHP. The respective limits of detection are 25 pptv and 15 pptv. Design, performance details, and illustrative results from a field campaign (Philadelphia NEO3PS study, 2001) are presented.     

High-sensitivity instrument for measuring atmospheric NO2

We report on the development of a high-sensitivity detection system for measuring atmospheric NO2 using a laser-induced fluorescence (LIF) technique around 440 nm. A tunable broad-band optical parametric oscillator laser pumped by the third harmonic of a Nd:YAG laser is used as a fluorescence excitation source. The laser wavelength is tuned at peak and bottom wavelengths around 440 nm alternatively, and the difference signal at the two wavelengths is used to extract the NO2 concentration. This procedure can give a good selectivity for NO2 and avoid interferences of fluorescent or particulate species other than NO2 in the sample air. The NO2 instrument developed has a sensitivity of 30 pptv in 10 s and S/N = 2. The practical performance of the detection system is tested in the suburban area for 24 h. The intercomparisons between the LIF instrument and a photofragmentation chemiluminescence (PF-CL) instrument have been performed under laboratory conditions. The correlation between the two instruments is measured up to 1000 pptv. A good linear relationship between the LIF measurements and the PF-CL measurements is obtained.     

A virtual instrument for measurement of flicker

All types of fluctuations of the rms voltage in power systems may be assessed by using a “flickermeter” which complies with the specifications given in IEC-EN 60868. In this paper, a digital flickermeter is presented based on the implementation in the frequency domain of the weighting filter block of the eye-brain simulation chain. The virtual instrument, implemented with an acquisition board inserted into a PC and with a software developed with the LabView tools, samples the voltage and furnishes the instantaneous flicker level and other severity coefficients. Results of simulated and actual data are reported to validate the performance of the developed flickermeter     

机械振动测量虚拟仪器的设计

机械振动参数测量中信号变化频率高、数据处理工作量大、频谱分析所涉及的数学运算复杂,采用模拟式仪器很难达到测试要求,而数字式仪器又具有价格昂贵、功能不够灵活的缺点,针对以上特点,以l_abVlEW为开发环境设计了虚拟式机械振动测试和分析系统,系统采用普通的Pc机和数据采集卡,利用计算机强大的数据处理能力实现测量数据的波形显示、存储和打印等功能.实验结果表明,系统的结构简单、稳定性好,功能灵活、运算可靠.     

A digital signal-processing instrument for impedance measurement

A digital signal processing (DSP)-based instrument for impedance measurement is proposed. It implements two measurement techniques: the first technique allows the tracking of a time varying impedance to be carried out, and the second assures that good accuracy is obtained in reasonable measurement times. Both the software and the hardware of a prototype model are described in detail. The measurement rates and accuracy are evaluated and compared with those obtained using a reference Digibridge for a wide range of impedance values     

Noncontacting low-cost instrument for film thickness measurement

A low-cost, noncontacting, nondestructive technique is presented for measuring the thickness of thin liquid or solid films and coatings in real time by utilizing the resonance properties of microstrip structures. A new measurement system in which all the microwave components are internal to the instrument, thereby eliminating the need for microwave test equipment, is described. Only a low-voltage DC source, such as a battery, is required to power the unit; the output is also a DC voltage or current. Using a linear model, sample coefficients of determination, r², greater than 0.98 have been obtained for film thickness measurements of water, enamel paint, and silicon rubber up to 0.8-1.5- and 2-mm thick, respectively. Copper sheet metal up to 0.9-mm thick has been measured with an r² greater than 0.99. The measurement range can be extended or improved even further if nonlinear circuit behavior is accounted for     

A biofilter design tool for hydrogen sulfide removal calculations

Biofilters have been used for decades in the management of nuisance odors that are emitted from the collection and treatment systems of municipal sewage works. Typically hydrogen sulfide (H₂S) has been identified as the major odor contributor associated with waste water treatment applications. H₂S can be recognized at concentrations of even less than 0.0047?ppm, thus H₂S removal systems must have efficiencies exceeding 99% for complete removal of odor from plant facilities. In order to accurately size biofilters for wastewater industries a predictive software tool is required. In this study, based on biofiltration removal kinetics of H₂S, a mathematical model has been incorporated into computer software which allows users to design biofilters for municipal wastewater applications, and estimate pre-air conditioning and energy requirements for smooth operations biofilters.