A novel ion detector aiming at the homogeneous of drift gas

In standalone ion mobility spectrometry (IMS) instruments, the effect of drift gas turbulence reduces the sensitivity and resolution of the instrument. A traditional ion detector constructed with a Faraday plate and used to detect ions in an IMS is positioned at the end of the drift region. Drift gas flowing through this detector may introduce turbulence near the detector, possibly affecting the sensitivity and resolution of the device. To address this problem, a novel Faraday detector with a double layer structure was constructed. A number of dense and staggered holes were created on each layer of the detector. This design enabled the drift gas to pass through the holes of the detector, and the staggered nature of holes in the detector ensured that the ions could be detected. Theoretical simulations were conducted using the finite element method to obtain velocity distributions for both a standard Faraday detector and the modified Faraday detector. The results indicated that the novel ion detector created a homogenous gas under at high inlet flow rate while turbulence was still evident for the traditional Faraday detector. When the inlet flow rate was 1000 mL/min, the range of the unstable region of the drift gas in the axis of the drift tube with the novel ion detector was reduced by 97% relative to that for the traditional detector. The data suggests that due to such gains, sensitivity and resolution may be improved for standalone IMS instruments.     

气相色谱仪检定装置的使用方法

依据JJG 700–1999《气相色谱仪检定规程》介绍气相色谱仪检定装置的使用方法。检定项目包括载气流速稳定性、柱箱温度稳定性和程序升温重复性、衰减器换挡误差以及检测器的灵敏度。给出了热导检测器(TCD)、火焰离子化检测器(FID)、火焰光度检测器(FPD)、电子俘获检测器(ECD)和氮磷检测器(NPD)检定时的色谱条件及使用注意事项。正确使用气相色谱仪检定装置能保证仪器测量数据的准确可靠。     

Comparison of different detectors for amino acid analysis

Summary Three different detectors for gas chromatography are compared in respect to sensitivity and selectivity: the flame-ionization detector, the nitrogen-selective alkali-flame ionization detector and the electron-capture detector. Their suitability for amino acid analysis is discussed, especially concerning sensitivity and linearity of detection. The nitrogen-selective detector proved to be most suitable both in respect to sensitivity and selectivity. The detection limit is in the range of less than 1 pg using the nitrogen-selective detector, about 1 – 2 pg with the electron-capture detector and about 5 –15 pg using the flame-ionization detector.

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Vergleich verschiedener Detektoren für die Analyse von Aminosäuren

     

Compton suppression system at Penn State Radiation Science and Engineering Center

A Compton suppression system is used to reduce the contribution of scattered gamma-rays that originate within the HPGe detector to the gamma-ray spectrum. The HPGe detector is surrounded by an assembly of guard detectors, usually NaI(T1). The HPGe and NaI(T1) detectors are operated in anti-coincidence mode. The NaI(T1) guard detector detects the photons that Compton scatter within, and subsequently escape from the HPGe detector. Since these photons are correlated with the partial energy deposition within the detector, much of the resulting Compton continuum can be subtracted from the spectrum reducing the unwanted background in gamma-ray spectra. A commercially available Compton suppression spectrometer (CSS) was purchased from Canberra Industries and tested at the Radiation Science and Engineering Center at Penn State University. The PSU-CSS includes a reverse bias HPGe detector, four annulus NaI(T1) detectors, a NaI(T1) plug detector, detector shields, data acquisition electronics, and a data processing computer. The HPGe detector is n-type with 54% relative efficiency. The guard detectors form an annulus with 9-inch diameter and 9-inch height, and have a plug detector that goes into/out of the annulus with the help of a special lift apparatus to raise/lower. The detector assembly is placed in a shielding cave. State-of-the-art electronics and software are used. The system was tested using standard sources, neutron activated NIST SRM sample and Dendrochronologically Dated Tree Ring samples. The PSU-CSS dramatically improved the peak-to-Compton ratio, up to 1000:1 for the ¹³⁷Cs source.     

毛细管电泳光学检测器的进展

对毛细管电泳的光学检测器作了简要评述。根据所采用的检测原理。光源检测器可分为紫外检测器，激光诱导荧光检测器、化学肆光检测器、荷耦合器件检测器、折射指数检测器等许多种类，具有简单方便、使用广泛，信息量较大等特点，是一类有良好诉检测器。     

A theoretical model of the electron capture detector

Summary This paper reports a theoretical model of the ECD detector. The model presented here can be used to examine the influence of pulse parameters on the current and signal characteristics of the detector. On the basis of this model it was found that a space charge is created in the detector when it is supplied with pulse voltage. Due to the electric potential generated by the space charge, in the time between the pulses the electrons and negative ions move towards the detector electrodes. The ionization current of the detector is the sum of the electron current flowing to the anode under the influence of the supplied pulse voltage and the current flowing under the space charge potential in the time between the pulses. It was also found that the detector signal is the sum of the differences between those two currents caused by introducing the sample molecules to the detector. The model was tested for a detector with different electrode configurations which worked at temperature of 300 K or 573 K and which was supplied with nitrogen or Ar+10% CH₄ as the carrier gas.     

Interpolation and extrapolation of NaI detector efficiencies

The concept of representing a cylindrical detector volume as a virtual point detector in order to simplify the evaluation of the detector efficiency was proposed in the past for HPGe detectors in the case of measuring point sources. In the present work, the validity of the point detector model was studied and confirmed for the direct measurement of small volume sources, when using a common 7.5×7.5 cm² NaI(T1) detector.     

Estimation of the properties of an energy-dispersive X-ray fluorescence spectrometer based on a composite double-layer detector

A mathematical model of double-layer Si-Ge and Si-AsGa energy-dispersive detectors of X-rays based on the analysis of processes of radiation and electron transfer in the detector is proposed along with a model of an energy-dispersive X-ray fluorescence spectrometer on the basis of this detector. The probabilities of recording of photons in different sections of the detector response function are calculated using the Monte-Carlo technique. It is shown that, in using an anticoincidence circuit and a Si detector as the first layer and Ge or AsGa detectors as the second layer, a detector with improved characteristics can be obtained, namely, the suppressed loss peaks of Ge or As and Ga and the efficiency of detection at the high radiation energy close to that of the Ge or AsGa detector. This detector in the energy-dispersive X-ray fluorescence spectrometer in some cases allows the reduction of the background level.     

Effects of contamination on ion mobility detection after gas chromatography

The ion mobility detector is a device that can be used for the selective, ultratrace detection of organic compounds after capillary gas chromatography. It is the only gas chromatographic detector which does not require heteroatomic compounds for selective response, yet concern is often expressed over its quantitative capabilities. Being a secondary ionization device, competitive charge transfer reactions from unseparated compounds or detector gas contamination may decrease the accuracy of measurement. This paper investigates the effects of both electronegative and electro-positive contaminants on the detector's response. In general, it was found that contamination of the detector did affect response but no more severely than in conventional detectors such as the electron-capture detector or the flame ionization detector.     

Evaluation and comparison of selective gas chromatographic detectors for the analysis of pesticide residues

Summary A series of studies is described on the evaluation and comparison of some selective gas chromatographic detectors used in pesticide residue analysis. A detailed study of the optimization and response characteristics of the CsBr and RbCl three-electrode alkali flame ionization detector for N and P compounds, the Coulson electrolytic conductivity detector in the nitrogen, sulphur and pyrolytic modes of operation and the sulphur phosphorus emission detector, a type of flame photometric detector, was carried out to obtain maximum sensitivity and reliability for the analysis of pesticide residues in various biological substrates. It was observed that the alkali flame and electrolytic conductivity detector responses to nitrogen compounds were of the same order, while the electrolytic conductivity detector was more sensitive than the flame photometric detector to sulphur compounds. Also, attempts were made to correlate the responses from these different detector systems using the insecticide chlorpyrifos which contains P, S, Cl and N atoms. The use of chlorpyrifos as an evaluation standard in verifying the acceptable performance of these types of detectors is recommended.Chemistry and Biology Research Institute Contribution No 901     

用于天文成像探测的IRFPA性能参数测试

天体的红外成像探测在天文学领域中有其特殊和重要的作用,高性能红外探测器是红外天文观测的关键器件,因此红外焦平面阵列探测器性能参数的测试评价对于红外天文观测具有非常重要的意义。针对天文应用的特殊性,通过分析红外焦平面阵列(Infrared focal plane array,IRFPA)探测器的特点,给出了增益、读出噪声、线性和暗流等性能参数的测试原理和方法,建立了测试平台,该测试平台可实现1~14μm波长范围的IRFPA探测器性能参数测试;完成了一台采用国产3~5μm HgCdTe芯片研制的IRFPA探测器性能参数的测试。测试结果表明,该IRFPA探测器的线性度非常好,可以达到99.9%以上,但读出噪声和暗电流较大,与国外为天文观测研制的高性能探测器相比尚有很大的差距。     

Advances in HPGe Detectors for Real-World Applications

Germanium detector use and crystal production has progressed to such a degree that the IEEE standard for the performance of the detector is no longer adequate to predict the efficacy for a different situation. The specifications of the standard do not predict how a detector will perform at other energies or geometries. One such geometry that is poorly predicted is extended sources. Many parts of the detector and electronics that can be changed to make the total system perform better for a specific case, but such changes can worsen the performance of the detector at the IEEE specification. Examples will be given for the efficiency, MDA, throughput, and resolution for different source—detector and crystal configurations.     

A computer program for calculating Ge(Li) detector counting efficiencies for Marinelli beakers

A novel computing method has been developed to calculate the absolute photopeak efficiency of a Ge(Li) detector for Marinelli beakers of different heights and diameters and with variable density. For each point in the cylindrical sample the detection efficiency is calculated taking into account the distance from the detector and gamma-ray attenuation and the efficiency is integrated numerically over the volume of the sample. The detector is approximated as a point detector with an experimentally determined effective interaction depth. It is necessary to measure the absolute efficiency for a point source located on the detector axis and on a line beside the detector parallel to the axis. The computer program calculates the absolute counting efficiency for Marinelli beakers of any geometry and for any density. The measured and calculated values for three different densities give a good (–2.2%) overall agreement.     

Impulse-response functions of several detectors used in flow-injection analysis

A procedure for the determination of the impulse-response function of a detector is given. Its application to photometers, ion-sensitive field effect transistors, a potentiometric detector at constant current and a voltammetric detector shows that the impulse-response function can be used to obtain specific information about the performance of the detector in the manifold. This function clearly shows the contribution of the detector to the peak broadening and how the detector generates the final signal from the presented concentration profile. From this information one could derive improvements to the detector, such as changing the construction of the detector cell, minimizing the influence of other parts of the manifold or adapting the attached electronics.     

Ultraviolet photodetector based on ZnO nanorods grown on a flexible PDMS substrate

A flexible, reproducible, sensitive and low-cost ultraviolet (UV) detector has been fabricated based on zinc oxide (ZnO) nanorods grown on a patterned polydimethylsiloxane (PDMS) substrate. The substrate was seeded with ZnO nanoparticles synthesised via simple low-temperature hydrothermal method using pomegranate peel extract as a reducing agent. The produced ZnO-nanorods/PDMS (ZnO-NR/PDMS) samples were tested for their UV-sensing properties. Samples were characterised using scanning electron microscopy, X-ray diffraction, I–V characteristics, UV-Vis spectroscopy and photoluminescence measurements. The UV photoresponse mechanism of prototype UV detector was analysed. The detector exhibited quite high on/off ratios between photoresponse current and dark current. With the flexible PDMS substrate, the detector photoresponse was tested with and without bending and exhibited a very slight change in the photoresponse current. The detector current–time response was also tested under various UV light intensities for three test cycles to examine the detector stability, hysteresis behaviour and performance. It is anticipated that the fabrication of ZnO-NR/PDMS UV detector may have significant potential application in flexible optoelectronic devices.     

Semiconductor Detector for Gas Leakages from a Main Line without Digging Ground

A chromatographic semiconductor detector was developed for an instrument designed for finding main-line gas leaks without digging. The sensing element of the detector is an adsorption semiconductor sensor based on tin dioxide doped with antimony and containing palladium additives. The optimum operation conditions of the sensor as a chromatographic detector were determined. The detector was highly sensitive to hydrocarbons (to 0.5 ppm in terms of CH₄). The stability of the developed detectors was examined.     

Microchip Capillary Electrophoresis‐Electrochemistry with Rigid Graphite‐Epoxy Composite Detector

A new rigid graphite‐epoxy composite electrode for electrochemical detection in microchip electrophoresis is described. The end‐column wall‐jet detection design relying on tubular rigid composite working electrode shows favorably low noise level and high signal‐to‐noise ratio when compared to glassy carbon detector. The performance of rigid graphite‐epoxy composite detector was compared to glassy carbon detector using dopamine and catechol as model analytes. The various parameters of the microchip electrophoresis‐rigid graphite‐epoxy composite detector were optimized.     

A helium ionization detector with a thermionic electron emitter for gas chromatography

The principal circuit of a helium ionization detector with a thermionic electron emitter (He-IDTEE) is described. The detector works at atmospheric pressure. The characteristics of the detector were studied. The difference between the voltammetric characteristics of He-IDTEE and that of a helium ionization detector with a radioactive source was shown. The dependences of the analytical signal, background signal, and noise on an accelerating voltage were analyzed. The dependences of the signal-to-noise ratio on the accelerating voltage were studied at different cathode temperatures. The optimal working conditions of the detector were selected. The detection threshold and linear dynamic range were measured. For isobutane, they were 3 × 10^?9 vol % and 2–4 orders of magnitude, respectively.     

利用凝胶渗透色谱示差-紫外检测器联用测定丁苯共聚物的组成分布

将凝胶渗透色谱(GPC)中的示差与紫外检测器联用,测定了无规共聚丁苯橡胶和SBS三元嵌段共聚物中各级分的组成变化.实验方法选择中对比了两种浓度参数的确定方法,发现通过改变注射量来实现浓度变化的方法优于使用系列浓度样品的方法.分别测定标准样品在紫外和示差检测器上信号产生的时间间隔可以确定两个检测器上信号的时间差.根据紫外-示差检测器联用可以看到SBR无规共聚物和三嵌段SBS共聚物样品中每一个级分中随着相对分子质量的变化,苯乙烯含量的变化.     

Gas chromatographic determination of organolead compounds with an alternating current plasma detector

The performance of the gas chromatography/alternating current plasma detector as a selective detector for organolead compounds is investigated. The helium make-up flow rate and the spatial position from which the lead emission is viewed, have an effect on the detector response. The detection limit for tetrabutyl lead was established as 130 pg/s and the lead selectivity ratio was found to exceed 13,800. Some applications of organolead determination in complex matrices were also studied in order to demonstrate the selectivity and sensitivity of the alternating current plasma detector.