A new approach for radon monitoring in soil as an earthquake precursor using optical fiber

Temporal variations of radon concentration in soil before the earthquake are known as an earthquake precursor. For using of radon as an earthquake precursor, it is necessary to constantly monitor radon concentration variations in a relatively wide range in the vicinity of a fault which is virtually impossible for radon detectors that already exist. This paper proposes a new method for continuous measurement of radon concentration variations in a wide range, using optical fiber as radon detector. For this purpose, an experimental system consisting of radon source, optical-fiber holding chamber, radon gas detector, optical laser source, and optical power meter have been arranged to with the aim to create different concentrations of radon gas in the vicinity of the optical fiber; the attenuation which creates on optical fiber is subsequently measured. As a result, the average of the attenuation is 0.004 μw per each meter per Bq/l since the fault’s length is more than ten kilometers; sensitivity of the measurement can be improved many times over.     

Evaluation of the performance of various universal and selective detectors for sulfur determination in natural gas

In the present contribution, the performance of a number of commercially available selective and universal detectors that can be used in the analysis of sulfur components in natural gas is evaluated in terms of sensitivity, selectivity, reproducibility, quenching effect, stability, and compound dependence of the sulfur response. Investigated detectors include the sulfur chemiluminescnce, the flame photometric, the electron capture, the mass spectrometric, the thermal conductivity, and the flame ionization detector. The sulfur chemiluminescence detector was found to have the best overall performance, e.g., low picogram amounts of sulfur can be detected accurately and the linear dynamic range is more than five orders of magnitude. After careful optimization, the sulfur response of this detector was found to be almost compound independent. All other detectors, including the flame photometric and the electron capture detector, have more or less compound dependent responses.     

气相色谱用氦直流等离子体离子化检测器的研究

报道三种不同类型的气相色谱用氦直流等离子体离子化检测器。以氦气为载气和工作气体, 白金电极为放电电极, 通过测量检测器的工作参数, 考察了检测器对H2, O2, Ar, N2, CH4, CO, CO2等永久气体的响应特性及分析性能, 并应用于实际样品分析。对检测器的离子化机理进行了研究和探讨。     

A simultaneous multielement non-dispersive atomic-fluorescence spectrometer using modulated sources and frequency discrimination of fluorescence signals

Commercial radiofrequency-excited electrodeless discharge lamps can be run from a square-wave modulated power supply so as to give a low level of continuous emission when modulated in the frequency range 3–10 kHz. Use of a different modulation frequency and lock-in amplifier for each lamp allows multielement non-dispersive atomic-fluorescence spectrometry to be performed. Very low detection limits have been obtained for arsenic, selenium, tin and mercury. The use of low-cost electronic components in the system largely offsets the high cost of the individual excitation power supplies and tuned a.c. detectors.     

高精度四极质谱检测限测试和影响因素分析

高精度四极质谱仪(QMS)的气体分压精确测量功能与其使用方法关系密切.采用包含有四极质谱仪、真空系统和进样系统的质谱参数测试装置,针对工作及系统参数对质谱测试结果的影响开展研究.试验结果表明:无论是扫描速率、质量数分辨率、电压和探测器等质谱工作参数,还是真空本底、工作真空和气体种类等系统参数都会对质谱测试结果尤其检测限产生一定影响.试验获得了特定条件下的最优参数并进行比较.采用获得的最优参数组合,通过测量空气中极低含量稀有氪气和氙气的同位素谱图,可获得一定条件下法拉第杯(FC)、二次电子倍增器(SEM)和离子计数器(CP)等3种探测器的最小可检浓度,分别为17.3×10-9、0.34×10-9和0.15×10-9.其中SEM和CP的检测限最低,适合用于微量气体分析.     

Analysis of pesticide residues in fruits, vegetables, and milk by gas chromatography/tandem mass spectrometry.

A method for detection, quantitation, and confirmation of more than 100 pesticides by gas chromatography (GC) with ion trap mass spectrometry (MS/MS) has been developed. The sensitivity of this method for many analytes is equal to or lower than those of selective GC detectors such as flame photometric detectors and electrolytic conductivity detectors. Using MS/MS, very low detection limits and good confirmation (1 precursor ion and 2 or more product ions) are achieved simultaneously. The entire list of pesticides is screened with 2 injections per sample. Samples are introduced onto the column by a temperature-programmed cold injection to maximize response. Each pesticide is run with its own unique set of parameters, which fragment the compound, retaining only the precursor ion. This ion is then refragmented to create a product spectrum. The selectivity of MS/MS gives a very clean spectrum, making compound identification and confirmation clear, even with a relatively dirty food matrix. If care is taken to maintain the injection port and guard column, this method can reliably identify and confirm more than 100 pesticides at the low parts-per-billion range.     

X-ray spectrometry in the eighties

X-ray fluorescent spectroscopy anno 1983 is a superb analytical technique which allows precisions of one part in 2000. The main impediments to reaching this accuracy are sampling and sample preparation. Nevertheless, very accurate results can be obtained on a wide variety of materials. After fusion, a wide range of oxides can be analyzed using one calibration.Recent advances in analytical instrumentation will further contribute to improved performance for specific analytical problems. the scandium side window tube is the first of a series of side window tubes which will greatly enhance light element performance. The developement of multilayer technology shows great promise for the improvement of light to ultra-light element dispersion. Advances in detector technology will mainly be reached through selecting gas detectors per element range, and the use of high resolution gas detectors such as the gas scintillation proportional counter. Data treatment will show improvements through the increased use of fundamental parameter methods using theoretical alphas, on-line fundemental parameter calculations, or a combination of both. In addition, there will be a strongly increasing use of laboratory management systems which handle the automatic logging of samples and combine the XRF results with results from other techniques.Hardware in Energy Dispersive Spectroscopy (EDS) has not shown major changes in recent years. The use of room temperature HgI₂ detectors with a resolution around 400 eV could be usefull for sorting or identification applications. In the field of EDS, some extremely usefull software packages have been developed. These include packages for the analysis of samples without standards, and packages to analyse coatings.     

The routine use of selective gas chromatographic detectors

Summary The availability of gas chromatographic detectors selective for phosphorus, sulfur, nitrogen and halogens and the possibility of their simultaneous operation with each other or with conventional universal detectors has tremendously increased the amount of qualitative information that can be gathered from an unknown sample. Selective detectors when used simultaneously permit the calculation of percentage ratios of heteroatoms which represent additional information for qualitative identification. Combination of parallel columns with selective detectors reduces the total time needed for analysis and introduces additional information due to the different polarity of the columns.     

Atomic spectroscopy with surface wave plasmas

The use of microwave induced plasmas, particularly of surface wave plasmas, as detectors in atomic emission spectrometry for elemental analysis is reviewed. Surface wave plasmas have been produced at low HF power and used as gas chromatographic detectors. The analytical performances for the detection of non-metals with a Fourier transform spectrometer and a two-channel filter unit are reported. The excitation behavior of non-metals in helium-based mixed gas-plasmas has also be studied. In particular, the effect of power and of nitrogen concentration on the bromine emission has been systematically investigated. A nine-fold improvement of the detection limits for bromine can be obtained in a high power (900 W) helium-nitrogen (0.1-0.2%) plasma.     

Size‐exclusion chromatography for the determination of the boiling point distribution of high‐boiling petroleum fractions

The paper describes a new procedure for the determination of boiling point distribution of high‐boiling petroleum fractions using size‐exclusion chromatography with refractive index detection. Thus far, the determination of boiling range distribution by chromatography has been accomplished using simulated distillation with gas chromatography with flame ionization detection. This study revealed that in spite of substantial differences in the separation mechanism and the detection mode, the size‐exclusion chromatography technique yields similar results for the determination of boiling point distribution compared with simulated distillation and novel empty column gas chromatography. The developed procedure using size‐exclusion chromatography has a substantial applicability, especially for the determination of exact final boiling point values for high‐boiling mixtures, for which a standard high‐temperature simulated distillation would have to be used. In this case, the precision of final boiling point determination is low due to the high final temperatures of the gas chromatograph oven and an insufficient thermal stability of both the gas chromatography stationary phase and the sample. Additionally, the use of high‐performance liquid chromatography detectors more sensitive than refractive index detection allows a lower detection limit for high‐molar‐mass aromatic compounds, and thus increases the sensitivity of final boiling point determination.     

Methods in high resolution gas chromatography. Two-dimensional techniques

Basic methodology to effect the separation of complex samples by gas chromatography is discussed from an experimental point of view. Several possibilities are presented which are commonly used to enhance the information content of a gas chromatographic run. These include incorporation of more than one set of retention data, multiple detectors, and special column switching techniques. These and other techniques have sometimes been labeled “multidimensional” in the literature. An attempt is made to define the term “two-dimensional chromatography”. The review is divided into sections which point out the different directions which have been taken to deconvolute chromatographically unresolved components. Particular emphasis is placed on technology which is capable of dealing with samples of extreme complexity, and instrumentation for trace- and ultratrace analysis is dicussed with specific examples. The future of two-dimensional techniques in gas chromatography is looked into.     

Comparison of the response of four aerosol detectors used with ultra high pressure liquid chromatography

The responses of four different types of aerosol detectors have been evaluated and compared to establish their potential use as a universal detector in conjunction with ultra high pressure liquid chromatography (UHPLC). Two charged-aerosol detectors, namely Corona CAD and Corona Ultra, and also two different types of light-scattering detectors (an evaporative light scattering detector, and a nano-quantity analyte detector [NQAD]) were evaluated. The responses of these detectors were systematically investigated under changing experimental and instrumental parameters, such as the mobile phase flow-rate, analyte concentration, mobile phase composition, nebulizer temperature, evaporator temperature, evaporator gas flow-rate and instrumental signal filtering after detection. It was found that these parameters exerted non-linear effects on the responses of the aerosol detectors and must therefore be considered when designing analytical separation conditions, particularly when gradient elution is performed. Identical reversed-phase gradient separations were compared on all four aerosol detectors and further compared with UV detection at 200 nm. The aerosol detectors were able to detect all 11 analytes in a test set comprising species having a variety of physicochemical properties, whilst UV detection was applicable only to those analytes containing chromophores. The reproducibility of the detector response for 11 analytes over 10 consecutive separations was found to be approximately 5% for the charged-aerosol detectors and approximately 11% for the light-scattering detectors. The tested analytes included semi-volatile species which exhibited a more variable response on the aerosol detectors. Peak efficiencies were generally better on the aerosol detectors in comparison to UV detection and particularly so for the light-scattering detectors which exhibited efficiencies of around 110,000 plates per metre. Limits of detection were calculated using different mobile phase compositions and the NQAD detector was found to be the most sensitive (LOD of 10 ng/mL), followed by the Corona CAD (76 ng/mL), then UV detection at 200 nm (178 ng/mL) using an injection volume of 25 μL.     

气相色谱用微波诱导氩等离子体光离子化检测器的研究

本文报道了以Surfatron 表面波为激发器件的微波诱导氩等离子体光离子化检测器,以氩气为载气和工作气体,研究了三种不同类型检测器的结构性能, 通过测量检测器的工作参数及苯的检出限等,对检测器的基本特性和离子化机理进行了探讨,并应用于实际样品分析,结果令人满意     

Methods in high resolution gas chromatography. Two-dimensional techniques

Basic methodology to effect the separation of complex samples by gas chromatography is discussed from an experimental point of view. Several possibilities are presented which are commonly used to enhance the information content of a gas chromatographic run. These include incorporation of more than one set of retention data, multiple detectors, and special column switching techniques. These and other techniques have sometimes been labeled “multidimensional” in the literature. An attempt is made to define the term “two-dimensional chromatography”. The review is divided into sections which point out the different directions which have been taken to deconvolute chromatographically unresolved components. Particular emphasis is placed on technology which is capable of dealing with samples of extreme complexity, and instrumentation for trace- and ultratrace analysis is dicussed with specific examples. The future of two-dimensional techniques in gas chromatography is looked into.     

Scintillating-Glass-Fiber Neutron Sensors, their Application and Performance for Plutonium Detection and Monitoring

Most neutron detection sensors presently employ ³He gas-filled detectors. Despite their excellent performance and widespread use, there are significant limitations to this technology. A significant alternative neutron sensor utilizing neutron-active material incorporated into a glass scintillator is presented that offers novel commercial sensors not possible or practical with gas tube technology. The scintillating optical fiber permits sensors with a multitude of sizes ranging from devices of a single fiber of 150µm to sensors with tens of thousands of fibers with areas as large as 5 m² depending on the neutron flux to be measured. A second significant advantage is the use of high-speed electronics that allow a greater dynamic range, not possible with gas detectors. These sensors are flexible, conformable and less sensitive to vibration that optimizes the source-to-detector geometry and provides robust performance in field applications. The glass-fibers are sensitive to both gamma-rays and neutrons. However, the coincidence electronics are optimized for neutron to gamma-ray discrimination allowing very sensitive measurements with a low false-alarm rate. Applications include SNM surveillance, material control and accountability (MC&A), safeguard inspections, Pu health physics/bioassay and environmental characterization.     

Methods in high resolution gas chromatography. Two-dimensional techniques

Basic methodology to effect the separation of complex samples by gas chromatography is discussed from an experimental point of view. Several possibilities are presented which are commonly used to enhance the information content of a gas chromatographic run. These include incorporation of more than one set of retention data, multiple detectors, and special column switching techniques. These and other techniques have sometimes been labeled “multidimensional” in the literature. An attempt is made to define the term “two-dimensional chromatography”. The review is divided into sections which point out the different directions which have been taken to deconvolute chromatographically unresolved components. Particular emphasis is placed on technology which is capable of dealing with samples of extreme complexity, and instrumentation for trace- and ultratrace analysis is dicussed with specific examples. The future of two-dimensional techniques in gas chromatography is looked into.     

CONCURRENT SYNTHESIS OF METHANOL AND METHYLFORMATE CATALYZED BY COPPER-BASED CATALYSTS III. INFLUENCES OF CONCENTRATIONS OF CATALYSTSAND PROMOTERS

The influences of concentrations of catalysts and promoters on the catalytic activity and methyl formate selectivity in the cocurrent synthesis of methanol and methyl formate from synthesis gas at low temperature and pressure in a slurry phase catalyzed heterogeneously by copper-based catalysts have been studied. The experimental results exhibit that the catalytic activity goes up regularly with the increase of catalyst concentration and promoter concentration in the experimental range over all the tested catalysts.     

Atomic spectroscopy with surface wave plasmas

The use of microwave induced plasmas, particularly of surface wave plasmas, as detectors in atomic emission spectrometry for elemental analysis is reviewed. Surface wave plasmas have been produced at low HF power and used as gas chromatographic detectors. The analytical performances for the detection of non-metals with a Fourier transform spectrometer and a two-channel filter unit are reported. The excitation behavior of non-metals in helium-based mixed gas-plasmas has also be studied. In particular, the effect of power and of nitrogen concentration on the bromine emission has been systematically investigated. A nine-fold improvement of the detection limits for bromine can be obtained in a high power (900 W) helium-nitrogen (0.1–0.2%) plasma.     

Detection limits of thermal conductivity and photoionization detectors in high speed narrow bore CGC

Not only the required input band width and the availability of compatible instrumentation limit the reduction of column diameter but so do the column sample capacity and detector characteristics, such as volume and sensitivity. In this paper the scope and limitations of thermal conductivity and photoionization detection at atmospheric and reduced pressures for capillary gas chromatography are discussed at length. It is shown that the sensitivity of a thermal conductivity detector is inversely proportional to the pressure. Reduction of cell volume and decrease of pressure appear equivalent with respect to minimum detectable amount and peak broadening. This results in femtogram detection limits for column diameters as low as 10 μm. For photoionization detectors the sensitivity did not improve at reduced pressures, so that the effect of reduced pressure and addition of make-up gas on the detection limits is the same. Nevertheless, the applicability of a low volume photoionization detector (40 μl) for capillary columns with a diameter as low as 50 μm will be demonstrated by series coupled PID and FID detectors and illustrated with various applications.