消除水汽吸收峰干扰的红外光谱测量方法

红外光谱测量时,水汽吸收潜带常掩蔽重要的样品光谱信息.克服水汽干扰的方法有真空技术、干燥气体吹扫技术、样品穿梭技术、光谱差减技术和水汽补偿湿度滴定方法等.该文重点评述了新近发展的用于除去水汽噪音的湿度滴定法.不同于以往方法,该方法允许水汽带在光谱采集前期出现,并根据水汽吸收带的大小和正负方向,适时向光谱仪样品室通入干燥...     

Freeze-etching and vapor matrix deposition for ToF-SIMS imaging of single cells

Freeze-etching, the practice of removing excess surface water from a sample through sublimation into the vacuum of the analysis environment, has been extensively used in conjunction with electron microscopy. Here, we apply this technique to time-of-flight secondary-ion mass spectrometry (ToF-SIMS) imaging of cryogenically preserved single cells. By removing the excess water which condenses onto the sample in vacuo, a uniform surface is produced that is ideal for imaging by static SIMS. We demonstrate that the conditions employed to remove deposited water do not adversely affect cell morphology and do not redistribute molecules in the topmost surface layers. In addition, we found water can be controllably redeposited onto the sample at temperatures below -100 degrees C in vacuum. The redeposited water increases the ionization of characteristic fragments of biologically interesting molecules 2-fold without loss of spatial resolution. The utilization of freeze-etch methodology will increase the reliability of cryogenic sample preparations for SIMS analysis by providing greater control of the surface environment. Using these procedures, we have obtained high quality spectra with both atomic bombardment as well as C 60 (+) cluster ion bombardment.     

Analysis of Organic Pollutants in Surface Water by Solid-Phase Extraction and Gas Chromatograph-Mass Spectrometry

Solid-phase extraction (SPE) is an emerging chromatographic sample preparation technique. The novel extraction technique can reduce the time and volume of organic solvents required, and alleviate problems associated with the formation of emulsions as compared to conventional liquid-liquid extractions. This study was designed to apply SPE vacuum manifold to determine organic pollutants in surface water of Huan River binding with GC-MSD system.     

Determination of deuterium in organic compounds by infrared spectrophotometry

The Trenner-Arison-Walker method for the micro-analysis of deuterium in organic compounds involves oxidation of the compound with copper oxide in a sealed tube, collection of the water by vacuum distillation, and analysis of the water by infrared spectrophotometry. Experience in applying this technique to a variety of organic compounds in our laboratory has suggested a number of procedural modifications. These principally affect the methods of sample handling and water collection. Difficulties associated with temperature changes on the spectrophotometry of the deuterium-enriched water are overcome by differential analysis against natural-abundance water using a double-beam spectrophotometer.     

Effect of quenching time and quenching agent dose on total organic halogen measurement

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX measurement involves concentration of halogenated organic DBPs by adsorption onto activated carbon. Prior to activated carbon adsorption, quenching the chlorine residual in a water sample is an indispensable step to eliminate the positive interference resulting from continued chlorination with organic compounds adsorbed on the activated carbon surface or with the activated carbon surface itself. Arsenite is generally applied as the quenching agent. In this study, the arsenite quenching agent dose that was 100% of the stoichiometric amount of the chlorine residual in a water sample was demonstrated to be most appropriate. In practice, to ensure complete reduction of chlorine residual, slight overdose of arsenite is often recommended, but this was found to cause negative interferences in the TOX measurement due to two reasons. First, the competitive adsorption existed between halogenated organic DBPs and the excessive arsenite on the activated carbon. This competitive adsorption effect was pronounced within a quenching time of 15?min. After 15?min of quenching, a large fraction of arsenite might have reacted with some easily-reduced halogenated DBPs to become arsenate, which is partially ionized at pH 2 and less likely adsorbed on the activated carbon. In this case, more halogenated organic DBPs could be adsorbed on the activated carbon, resulting in the measured TOX concentrations to be much closer to the actual one contained in the sample. Second, excessive arsenite might lead to reduction or decomposition of halogenated organic DBPs with a prolonged quenching time (>60?min). Thus, to avoid the negative interferences, the appropriate quenching time should be 15–60?min.     

Spectrofluorometric method for determination of the total mercury content in environmental samples — Waste waters

A highly selective spectrofluorometric method for the determination of total mercury (Hg) in waste waters is described. Fluorescence quenching of rhodamine B with Hg(II) in the presence of iodide, after a concentration step, is the basis of this sensitive method. All forms of mercury, including organic compounds, are pre-oxidized to ionic mercury by acidic potassium permanganate. The final and complete oxidation is achieved by adding potassium persulphate and heating. Hg(II) was reduced by tin(II) chloride and Hg vapour driven by an air stream into an absorption solution containing potassium permanganate and sulphuric acid, using a closed, recirculating air stream. In this solution fluorescence quenching of rhodamine B at an excitation wavelength of 485 nm and emission wavelength of 586 nm was measured. The recoveries were done by adding 3.0 g Hg/100 ml to each sample before the digestion. It was indicated that the recoveries for determining mercury in waste waters were 98.3%–102.7%. The method gives reliable results down to a concentration of 10 ng Hg/ml waste water.     

Two dimensional mapping of cancer cell extracts by liquid chromatography-capillary electrophoresis with ultraviolet absorbance detection

A two-dimensional liquid chromatography/capillary electrophoresis technique was developed for rapid and comprehensive mapping of cell extracts. The cell extracts were first separated by reversed-phase HPLC based on hydrophobicity. Fractions of the effluent from the HPLC system were collected into 96-well microtiter plates and dried under vacuum. The fractions were reconstituted with deionized water, separated by capillary array electrophoresis based on charge-to-size ratio, and detected by UV absorption at 214 nm. Prior to analysis by multiplexed capillary electrophoresis, the reconstituted fractions were concentrated on-column using large volume sample stacking with polarity switching. In this way, high-resolution analysis of even the minor components in the complicated mixture was possible.     

Analysis of aerosols for light elements by forward alpha scattering technique

By forward alpha scattering technique (FAST) light elements, from hydrogen through fluorine, are shown to be determined nondestructively and simultaneously, though these elements cannot be measured satisfactorily by any other physical method. We have studied on the application of this method to atmospheric aerosol, photochemical and aerosol, etc. It was assured that the whole mole ratio of aerosol can be determined by the cooperative application of the FAST and the conventional fluorescent X-ray analysis. FAST has been realized to give the water content of aerosol, although the sample should be analyzed in vacuum.     

The Photophysics of Thin Polymer Films of Poly-(meta-phenylene-co-2,5-dioctoxy-para-phenylenevinylene)

Summary.  We have investigated the effect of film preparation procedures on the photoluminescence efficiency of the luminescent co-polymer poly-(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV). The photoluminescence efficiency of PmPV films improved by up to 50% when the solution was degassed by bubbling argon gas through it prior to spin casting in an inert atmosphere and baking under vacuum. Photoinduced absorption and doping measurements show that this preparation method reduces polaron photogeneration, which reduces the photoluminescence (PL) yield through exciton quenching and excited state absorption. It is proposed that this sample preparation method increases interchain separation, reducing the formation of polarons and non-radiative quenching routes, thus resulting in increased PL efficiency. Received June 23, 2000. Accepted (revised) August 3, 2000     

Comparison of a modified Kjeldahl and a vacuum fusion technique for determination of nitrogen in tantalum alloys

Results obtained for the determination of nitrogen in the tantalum alloys T-111 (Ta-8 W-2 Hf) and T-222 (Ta-10 W-2.5 Hf-0,1C) by Kjeldahl and vacuum fusion procedures are compared. Results obtained by each technique are shown for the determination of nitrogen m the MAB T-111 sample, two commercial T-111 samples and a commercial sample of T-222 alloy. In the 5-25 ppm range, the relative standard deviation was 3-9% by the Kjeldahl procedure and 4-8% by vacuum fusion. This is a measure of the homogeneity of the material as well as of the reproducibility of the results. The agreement of the results obtained by these two techniques increases confidence in the vacuum fusion results for nitrogen in tantalum.     

The application of microbalance technique in study of the high temperature superconductors

Many physical-chemical properties of oxide superconductors depend on oxygen content and its distribution in the sample. Investigations of the thermal decomposition of the oxide superconductors in dynamic vacuum are valuable, particularly in view of the high oxygen diffusion coefficient in these cuprates. Dynamic vacuum protects against the readsorption of oxygen from the environment. Samples of the high-temperature superconductors were synthesised from stoichiometric mixtures of high-purity oxides and carbonates.The lattice parameters of all preparations were controlled, in both initial and final experiments using a Stadi P (Stoe) diffractometer with a positron-sensitive detector (CuK radiation). The oxygen content was measured by iodometric titration with a reproducibility of at least 0.02.DC four probe resistivity measurements were performed on pellets to which copper contacts were attached by using silver paint. Thermogravimetric analyses (TG) were performed by using a Cahn RG ultramicrobalance system.The purpose of the present paper is to show the application of microbalance technique in study of high-temperature superconductors.This revised version was published online in November 2005 with corrections to the Cover Date.     

Determination of caffeine in solid pharmaceutical samples by FTIR spectroscopy

Fourier transform infrared spectroscopy has been used for the quantitative determination of caffeine in several pharmaceutical products: acetyl salicylic acid, paracetamol and propyphenazone. The method is simple, rapid and selective, and allows the determination of caffeine without sample pretreatment and without separation from the matrix. Two techniques for measuring the infrared spectra of caffeine are described: transmission through pellets and diffuse reflectance from powder (DRIFT). In both methods, samples were diluted (1%) with KBr. Caffeine in pharmaceutical matrices was recovered within 5% error in pellets and 10% by DRIFT. Relative standard deviations were generally 1.5% for repeated measurements on a single pellet and 5% for measurements on different pellets. DRIFT in the vacuum mode gave rather large RSDs. The limit of detection of the pellet technique was about 0.5% caffeine in the original sample.     

A novel hybrid mode of sample injection to enhance CZE sensitivity for simultaneous determination of a pyridine-triphenylborane anti-fouling agent and its degradation products

We developed a novel hybrid sample injection mode (HSIM) that presents the combination of electrokinetic injection and vacuum injection to enhance detection sensitivity in CZE. Samples were introduced using both vacuum and electrokinetic injections simultaneously, with a water plug injected into the capillary prior to sample introduction (i.e. similarly to field-amplified sample injection, FASI). Using a sample mixture containing an anti-fouling agent applied to ship hulls, pyridine-triphenylborane and its degradation products (diphenylborinic acid, phenylboronic acid, and phenol) dissolved in ACN, the length of water plug, time, and voltage for sample introduction were optimized. The signal intensity (peak height) was found to be up to a 30-fold increased using HSIM by applying 4 kV for 4 s at the inlet end of the capillary as the cathode with supplementary vacuum in comparison with only vacuum injection for 4 s. The LODs (at a S/N of 3) for pyridine-triphenylborane, diphenylborinic acid, phenylboronic acid, and phenol were 0.88, 1.0, 21, and 23 μg/L, respectively. At the level of 0.04 mg/L, the RSDs (n=4, intra-day) for the above analytes were in the ranges of 1.9-11, 4.3-9.2, and 0.34-0.66% for peak area, peak height, and migration time, respectively. The HSIM is a simple and promising procedure useful for enhancing the sensitivity for both low-and high-mobility ions in CZE.     

纳米水滴及真空中β-环糊精和对-甲基苯酚1:1包结物的约束动力学模拟研究

Two systems of 1: 1 inclusion of host β-cyclodextrin and guest p-cresol in nano-drip including 427 H2O molecules and in vacuum have been studied by the constrain molecular dynamics simulation technique with pcff force field and Rattle bond algorithm. The analysis on the dynamic structure of inclusion and radial distribution function of several kinds of oxygen atoms shows that the CD inclusion was stable during the simulation time period in two systems and none of water molecule was found to move into the CD cavity in the drip within 200 ps which conformed the hydrophobic property of CD cavity. In the drip,an obvious hydration caused by H-bonding existing in the CD hydrophilic outsides was observed,and it agreed well with the CD properties. The obvious H-bonding interactions existing between phenyl hydroxyl and water molecules in the drip and between phenyl hydroxyl and CD cavity in vacuum made the guest molecule insert into the CD cavity shallower in drip case than in vacuum case. It was concluded that the constrain molecular dynamics simulation technique can be used to investigate the dynamic behavior of CD aqueous solution.     

Čerenkov spectroscopic assay of fission isotopes

A erenkov counting technique is presented for the radioassay of¹⁰⁶Ru in aqueous solutions containing nitrate, nitric acid, chloride as well as inactive ruthenium nitrosyl complex carrier. The counting efficiency was found to be a function of colour quenching by these substances in the UV and visible range. Measurements made on a three-channel automatic liquid scintillation spectrometer indicated that the counting efficiency can be calculated by use of the experimentally determined channel ratio of a quenched sample, without prior knowledge of the quencher concentration. The technique can be useful during studies on the removal of¹⁰⁶Ru from nuclear waste solutions. Special settings of discriminator windows enable radioassays in presence of weak -emitters such as¹³⁷Cs. The possibility of determining¹⁰⁶Ru in presence of⁹⁰(Sr/Y) was also investigated.     

Study of the desorption/ionization mechanism in electrospray droplet impact secondary ion mass spectrometry

Electrospray droplet impact (EDI) secondary ion mass spectrometry (SIMS) is a desorption/ionization technique for mass spectrometry in which highly charged water clusters produced from an atmospheric-pressure electrospray are accelerated in vacuum by several kV and impact on the sample deposited on the metal substrate. The abundances of the secondary ions for C(60) and amino acids are measured as a function of the acceleration voltage of the primary charged water droplets. Two desorption/ionization mechanisms are suggested in the EDI ionization processes: low-energy and high-energy regimes. In the low-energy regime, the excess charges in the primary droplets play a role in the formation of secondary ions. In the high-energy regime, samples are ionized by the supersonic collision of the primary droplets with the sample. The yield of secondary ions increases by about three orders of magnitude with increase in the acceleration voltage of the primary droplets from 1.75 kV to 10 kV.     

Determination of trace amounts of molybdenum in water samples by inductively coupled plasma atomic emission spectrometry after cobalt-dithiocarbamate coprecipitation

Summary A method for the determination of trace amounts of molybdenum in fresh water and seawater samples by sequential ICP-AES with microsampling technique after cobalt-dithiocarbamate coprecipitation was developed. The precipitate was dissolved in 100 l of diluted nitric acid (1:2), and the solution obtained was then introduced into an ICP via a concentric nebulizer. By use of 1.7 ml sample, a preconcentration factor of 17 was achieved. Different factors including integration time, sample volume, pumping rate as well as coprecipitation conditions such as pH of the solution, amounts of reagents, standing time for the precipitate and matrix effects were examined and optimized in detail. Under selected conditions the detection limit of the method for Mo is 0.52 g/l using 1.7 ml sample. The procedure was applied to the analysis of water samples (artificial water and open ocean seawater reference material) with quantitative recovery. The analytical results were in good agreement with the certified value. The method is sensitive, simple, accurate and effective, also in the presence of interfering salts and can be applied to small sample volumes.On leave from the Department of Chemistry, Wuhan University, Wuhan, 430072 China     

Rapid determination of total trihalomethanes index in drinking water

A method for the rapid determination of total trihalomethanes (THMs) index in drinking water has been developed by using a headspace-mass spectrometry (HS-MS) system and partial least squares (PLS) multivariate regression approach. Due to the presence of residual amounts of chlorine and organic matter in the drinking water, the use of a quenching reagent in order to avoid THM generation during the sample manipulation is necessary. The optimization experiments revealed that ascorbic acid was the best quenching reagent compared with sodium thiosulfate and ammonium sulfate. The use of a classification chemometric technique as soft independent modeling of class analogy before the PLS regression improved the results obtained in the prediction of the total THMs index, lowering the relative standard error of prediction (RSEP) from 11.4% to lower than 6.0%. The results obtained by the proposed HS-MS method were compared with those provided by a conventional chromatographic method after analyzing 20 real drinking water samples. A good agreement in the results was observed and no systematic differences were found, which corroborates the good performance of the proposed method.     

Fluorescence Anisotropy Controlled by Light Quenching*

We demonstrated that fluorescence anisotropy can be effectively decreased or increased in the presence of light quenching, depending on relative polarizations of excitation and quenching pulses. For parallel light quenching, anisotropy decreases to 0.103 and z-axis symmetry is preserved. In the presence of perpendicular light quenching, the steady-state anisotropy of a pyridine-2-glycerol solution increases from 0.368 for an unquenched sample to 0.484 for a quenched one. We show that the angular distribution of transition moments loses z-axis symmetry in the presence of perpendicular light quenching. In these cases we used more general definitions of anisotropy. Induced by light quenching, anisotropy can be applied in both steady-state and time-resolved measurements. In particular, the systems with low or no anisotropy can be investigated with the proposed technique.     

High-temperature phase transitions in the La<Subscript>0.25</Subscript>Sr<Subscript>0.75</Subscript>FeO<Subscript>3−δ</Subscript> solid solution with a perovskite structure

Phase transformations in a sample from the series La_1?x Sr _x FeO_3?δ (x = 0.75) with cubic symmetry and perovskite type structure were studied by high-temperature X-ray diffraction. In air, the solid solution was stable to the synthesis temperature (1200°C), despite the loss of some part of oxygen. Heating in vacuum led to a two-phase state at 900°C (or even at 600°C when a small amount of palmitic acid was added to the sample); the unit cell parameter changed abruptly. The amount of the new phase increased with temperature, and at 1000°C, the sample, as well as the starting phase, was monophase perovskite with cubic symmetry; i.e., an isosymmetric phase transition occurred, which was accompanied by an abrupt change in the cell volume. Cooling in vacuum to ～800°C led to the ordering of the oxygen vacancies and the formation of a Grenier phase type structure. When the sample was heated again in vacuum, a reversible phase transition occurred from the Grenier phase type structure to a perovskite structure (again at ～800°C).