Evaluation of electrodeposited tungsten chemical modifier for direct determination of chromium in urine by ETAAS

The direct determination of chromium in urine by electrothermal atomic absorption spectrometry (ETAAS) using graphite tubes modified with tungsten is proposed. Modification of the graphite is made by tungsten electrodeposition over the whole surface atomizer followed by carbide formation by heating the tube inside its own furnace. For tungsten electrocoating, the graphite tube and a platinum electrode were connected to a power supply as cathode and anode, respectively, and immersed in a solution containing 2 mg of W in 0.1% v/v HNO₃. Then, 5 V was applied between the electrodes during 20 min for tungsten electrodeposition over the whole atomizer. A SpectrAA 220 Varian atomic absorption spectrometer equipped with a deuterium background corrector was used throughout. Undiluted urine (20 μl) was delivered over the tungsten-treated tube and the chromium-integrated absorbance was measured after applying a suitable heating program with maximum pyrolysis at 1300 °C and atomization at 2500 °C. With electrodeposited tungsten modifier, the tube lifetime increased up to four times when compared to previous published methods for Cr determination in urine by ETAAS, reaching 800 firings. Method detection limit (3 S.D.) was 0.10 μg l⁻¹, based on 10 integrated absorbance measurements of a urine sample with low Cr concentration. Two reference materials of urines (SRM 2670) from National Institute of Standards and Technology (NIST) were analyzed for method validation. For additional validation, results obtained from eight human urine samples were also analyzed in a spectrometer with Zeeman effect background correction.     

A new type of Zeeman-effect atomic-absorption spectrophotometer

A new type of Zeeman-effect atomic-absorption spectrophotometer has been developed. It uses fast heating of a special atomizer made from a pyro-coated graphite tube lined with tungsten-tantalum alloy, for easier determination of refractory and rare-earth elements. A boxcar integrator is used, and the atomic absorption, background absorption and atomization temperature can be recorded. By means of the Zeeman effect, the instrument can correct for background absorbance up to 2.0.     

Completely automated open-path FT-IR spectrometry

Atmospheric analysis by open-path Fourier-transform infrared (OP/FT-IR) spectrometry has been possible for over two decades but has not been widely used because of the limitations of the software of commercial instruments. In this paper, we describe the current state-of-the-art of the hardware and software that constitutes a contemporary OP/FT-IR spectrometer. We then describe advances that have been made in our laboratory that have enabled many of the limitations of this type of instrument to be overcome. These include not having to acquire a single-beam background spectrum that compensates for absorption features in the spectra of atmospheric water vapor and carbon dioxide. Instead, an easily measured “short path-length” background spectrum is used for calculation of each absorbance spectrum that is measured over a long path-length. To accomplish this goal, the algorithm used to calculate the concentrations of trace atmospheric molecules was changed from classical least-squares regression (CLS) to partial least-squares regression (PLS). For calibration, OP/FT-IR spectra are measured in pristine air over a wide variety of path-lengths, temperatures, and humidities, ratioed against a short-path background, and converted to absorbance; the reference spectrum of each analyte is then multiplied by randomly selected coefficients and added to these background spectra. Automatic baseline correction for small molecules with resolved rotational fine structure, such as ammonia and methane, is effected using wavelet transforms. A novel method of correcting for the effect of the nonlinear response of mercury cadmium telluride detectors is also incorporated. Finally, target factor analysis may be used to detect the onset of a given pollutant when its concentration exceeds a certain threshold. In this way, the concentration of atmospheric species has been obtained from OP/FT-IR spectra measured at intervals of 1 min over a period of many hours with no operator intervention.     

Determination of nanomolar concentrations of phosphate in natural waters using flow injection with a long path length liquid waveguide capillary cell and solid-state spectrophotometric detection

A flow injection manifold incorporating a 1 m liquid waveguide capillary cell and a miniature fibre-optic spectrometer for the determination of low phosphorus concentrations in natural waters is reported. The limit of detection (blank + 3 S.D.) was 10 nM using the molybdenum blue chemistry with tin(II) chloride reduction. The sensitivity of the flow injection manifold was improved by 100-fold compared with a conventional 1 cm flow cell. The response was measured at 710 nm and background corrected by subtracting the absorbance at 447 nm. Interference from silicate was effectively masked by the addition of 0.1% (m/v) tartaric acid and results were in good agreement (P = 0.05) with a segmented flow analyser reference method for freshwater samples containing 1 μM phosphate.     

Detection of atmospheric nitrogen dioxide using a miniaturised fibre-optic spectroscopy system and the ambient sunlight

A miniaturised fibre-optic spectrometer based system is presented for direct detection of one of the major atmospheric pollutants, nitrogen dioxide, by absorption spectroscopy using the ambient sunlight as light source. The detection system consists of a 10 cm collimator assembly, a fibre-optic cable and a portable diode-array spectrometer. The absorbance spectrum of the open-path is calculated using a reference spectrum recorded when the nitrogen dioxide (NO2) concentration in the atmosphere is low. The relative concentration of the pollutant is calculated normalising the detected spectra and subtracting the background broadband spectrum from the specific NO2 absorbance features, since the broadband spectrum changes according to atmospheric conditions and solar intensity. Wavelengths between 400 and 500 nm are used in order to maximise sensitivity and to avoid interference from other species. Calibration is carried out using Tedlar sample bags of known concentration of the pollutant. A commercial differential optical absorption spectroscopy (DOAS) system is used as a reference standard detection system to compare the results with the new system. Results show that detection of NO2 at typical urban atmospheric levels has been achieved using an inexpensive field based fibre-optic spectrometer and a readily available, easy to align, light source. In addition the new system can be used to get a semi-quantitative estimation of the nitrogen dioxide concentration within errors of 20%. While keeping the typical benefits of open-path techniques, the new system has important advantages over them such as cost, simplicity and portability.     

Computer-controlled switch for temperature ranging with a recording optical pyrometer

The measurement of temperature is a useful analytical probe for industrial processes as well as applied research. However, temperature ranges for most monitoring equipment are not designed to deal with the broad temperature ranges common in electrothermal atomization atomic absorption spectroscopy. A simple circuit that enhances the temperature ranging of a commercial recording optical pyrometer, specifically, an Ircon Series 1100 optical pyrometer, is presented. This circuit used with the included “pseudo-code” can measure an increasing or decreasing temperature over the range 1000–3000°C.     

Plasma spraying of alumina: Plasma and particle flow fields

A comprehensive experimental examination of the interaction between a subsonic thermal plasma jet and injected alumine, particles is presented. Measurements of plasma velocity, temperature, and entrained air were obtained from an enthalpy probe and mass spectrometer combination. A diffusive separation, or demixing, of the Ar and He plasma gas was observed. Centerline plasma velocities and temperatures ranged from 1501500 m/s and 2000 to 14,000 K, respectively, in the region between the torch and a typical substrate location of 90 mm. Measurements of particle size, velocity, tempearture and local number density were obtained from a combination laser particle sizing system, Laser doppler velocimeter (LDV), and two-color pyrometer. Centerline temperatures and velocities for the nominally 30 m particles used were 2400–2800 K and 150–200 m/s, respectively.     

Catalytic determination of trace manganese using initial redox reaction of Malachite Green and periodate

Malachite Green of 2.2×10^–5 M and sodium periodate of 3.4×10^–3 M were reacted at 48 °C and pH 3.3 in a cuvette of a spectrophotometer. The slight color fading at 615 nm was measured with a reference of an absorption plate of about 1.8 A, and was recorded on a strip chart as a function of time. From a tangent of the recorded linear trace, 2 to 200 ng Mn(II) was determined with a standard deviation (S. D.) of 0.5 ng within 10 min. Using the absorbance at the reaction time of 5 min, 5 to 30 ng was determined with a S. D. of 2 ng. Experimental conditions, sensitization and enhanced uncatalyzed reaction are discussed. The color fading of the wide absorbance range is also described for more than 200 ng Mn.     

Determination of boron isotope ratios by Zeeman effect background correction-graphite furnace atomic absorption spectrometry

A new method for the determination of isotopic ratio of boron using Zeeman effect background correction-graphite furnace atomic absorption spectrometry with conventional atomizer and natural-boron hollow cathode source is described. The isotope-shift Zeeman effect at 208.9 nm is utilized for isotopic ratio determination. At a given concentration of total boron, the net absorbance decreases linearly with increasing ¹⁰B/¹¹B ratio. The absorbances are recorded at the field strength of 1.0 T. The isotope ratios measured by the proposed method were in good agreement with the results obtained by inductively coupled plasma-quadruple mass spectrometry or thermal ionization mass spectrometry. The present method is fairly fast and less expensive compared to the above techniques and is quite suitable for plant environments.     

Critical behavior of 2,6-dimethylpyridine-water: measurements of specific heat, dynamic light scattering, and shear viscosity

The specific heat C(p) at constant pressure, the shear viscosity eta(s), and the mutual diffusion coefficient D of the 2,6-dimethylpyridine-water mixture of critical composition have been measured in the homogeneous phase at various temperatures near the lower critical demixing temperature T(c). The amplitude of the fluctuation correlation length xi(0)=(0.198+/-0.004) nm has been derived from a combined evaluation of the eta(s) and D data. This value is in reasonable agreement with the one obtained from the amplitude A(+)=(0.26+/-0.01) J(g K) of the critical term in the specific heat, using the two-scale-factor universality relation. Within the limits of error the relaxation rate Gamma of order parameter fluctuations follows power law with the theoretical universal exponent and with the amplitude Gamma=(25+/-1)x10(9) s(-1). No indications of interferences of the critical fluctuations with other elementary chemical reactions have been found. A noteworthy result is the agreement of the background viscosity eta(b), resulting from the treatment of eta(s) and D data, with the viscosity eta(s)(nu=0) extrapolated from high-frequency viscosity data. The latter have been measured in the frequency range of 5-130 MHz using a novel shear impedance spectrometer.     

High-precision isotopic ratio measurement system for methane (12CH3D/12CH4,13CH4/12CH4) by using near-infrared diode laser absorption spectroscopy

We demonstrate that the absorption spectroscopic method can be applied to a precise deltaD (an index of 12CH3D/12CH4) and delta13C (an index of 13CH4/12CH4) analysis for methane samples of natural isotopic abundance. We chose an appropriate absorption line pair whose absorption coefficients have nearly the same temperature dependences so as to minimize the temperature effect in absorbance ratio measurements. We measured 12CH3D/12CH4 ratio by using near-infrared external cavity diode lasers and a new type multi-pass cell. The deltaD value can be determined from the 12CH3D/12CH4 signal-intensity ratio with a fine correction by taking account of the interference of 13CH4 lines. Similarly, the delta13C value is determined from the 13CH4/12CH4 signal-intensity ratio, which is measured by using distributed-feedback laser and a modified Herriot-type cell and corrected for the abundance of 12CH3D. The precision was +/-0.7 and +/-0.027/1000 for deltaD and delta13C, respectively.     

Analysis of vitamin D and its metabolites using thermospray liquid chromatography/mass spectrometry.

A new method is described for the analysis of vitamin D and its metabolites utilizing thermospray (TSP) mass spectrometry as an on-line detector for high performance liquid chromatography. Ionization conditions were optimized for use with isocratic reversed phase chromatography. TSP mass spectrometry was employed in series with a UV absorbance detector to facilitate comparisons between the two methods of detection. Positive ion TSP mass spectra were recorded for vitamin D2, vitamin D3, 25-hydroxyvitamin D3 (25(OH)D3), 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3). The spectra contained protonated molecular ions, ammonium adduct ions and fragment ions due to the loss of one or more molecules of water. A comparison of quantitative precision was made by determining UV absorbance and TSP standard curves for vitamin D3 using two different methods: (1) External standard method with post-column (post UV detector) addition of ammonium acetate. (2) As (1) but using the method of internal standards with a closely eluting internal standard (vitamin D2). In each case the quantitative precision (correlation coefficient) for UV absorbance detection was superior owing to intrinsic instability of the TSP ion beam. A stable isotopically labelled internal standard was employed in the development of an assay for 1,25(OH)2D3. The assay was used to quantify in vitro enzymic conversion of 25(OH)D3 to 1,25(OH)2D3 in guinea pig and sheep renal mitochondrial incubations. TSP LC/MS was also applied to analysis of an extract of human blood plasma in which D3 and each of its principal metabolites were identified in a single analysis.     

Temperature and gas-phase composition measurements in supersonic flows using tunable diode laser absorption spectroscopy: the effect of condensation on the boundary-layer thickness

We used a tunable diode laser absorption spectrometer and a static-pressure probe to follow changes in temperature, vapor-phase concentration of D2O, and static pressure during condensation in a supersonic nozzle. Using the measured static-pressure ratio p/p0 and the mass fraction of the condensate g as inputs to the diabatic flow equations, we determined the area ratio (A/A*)wet and the corresponding centerline temperature of the flow during condensation. From (A/A*)wet we determined the boundary-layer displacement thickness during condensation (delta#)wet. We found that (delta#)wet first increases relative to the value of delta# in a dry expansion (delta#)Dry before becoming distinctly smaller than (delta#)Dry downstream of the condensation region. After correcting the temperature gradient across the boundary layers, the temperature determined from p/p0 and g agreed with the temperature determined by the laser-absorption measurements within our experimental error (+/-2 K), except when condensation occurred too close to the throat. The agreement between the two temperature measurements let us draw the following two conclusions. First, the differences in the temperature and mole fraction of D2O determined by the two experimental techniques, first observed in our previous study [P. Paci, Y. Zvinevich, S. Tanimura, B. E. Wyslouzil, M. Zahniser, J. Shorter, D. Nelson, and B. McManus, J. Chem. Phys. 121, 9964 (2004)], can be explained sufficiently by changes in delta# caused by the condensation of D2O, except when the phase transition occurs too close to the throat. Second, the extrapolation of the equation, which expresses the temperature dependence of the heat of vaporization of bulk D2O liquid, is a good estimate of the heat of condensation of supercooled D2O down to 210 K.     

Spectrophotometric determination of aqueous acidity constants of three azo dyes

The two successive steps acidity constants of three azo dye derivatives D1–D3, were determined by a spectrophotometric method using 0.10 M KNO₃ as supporting electrolyte in water solvent. The electronic spectra of the compounds were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants can be solved very satisfactorily from absorbance data, by combining the data obtained in the spectrometric determinations with graphic methods as the absorbance diagrams. An A-diagram shows the relative absorbance changes at two wavelengths as a function of the pH. For a one-step system, the absorbance at any wavelength must be proportional to the absorbance at any other wavelength, so an A-diagram for all wavelength combinations for such a system must be linear (rank, s=1). However, if a system is governed by two or more equilibria, the A-diagrams corresponding to multi-step titrations will change direction every time a new equilibrium becomes dominant in the system. Analysis of the each uniform sub-region can then be used in evaluating of the corresponding equilibrium. A-diagrams for all wavelength combinations suggest that these systems have the rank two(s=2). The results revealed that the K_a(1) and K_a(2) values of different azo dyes follow the order D3>D2>D1.      

燃料高速燃烧动态温度的测量

利用多通道高温计测量燃料高速燃烧动态温度的方法,在爆炸激波管中模拟异辛烷,正庚烷、正辛烷、正庚烷+异辛烷混合物等烷烃高速燃烧。并用该方法考察了氧气对异辛烷高速燃烧温度的影响,及上述烷烃的辛烷值与高速燃烧温度的关系。结果表明,对于富含异辛烷的混合物,增加氧含量可以使高速燃烧温度增加;随着烷烃辛烷值的增加,高速燃烧温度下降,与利用传感器测量结果相吻合。本文所述的方法可以用于各种气-液相混合物高速燃烧温度的测量。     

Gas-phase hydrogen/deuterium exchange as a molecular probe for the interaction of methanol and protonated peptides

The gas-phase hydrogen/deuterium (HID) exchange kinetics of several protonated amino acids and dipeptides under a background pressure of CH₃OD were determined in an external source Fourier transform mass spectrometer. H/D exchange reactions occur even when the gas-phase basicity of the compound is significantly larger (> 20 kcal/mol) than methanol. In addition; greater deuterium incorporation is observed for compounds that have multiple sites of similar basicities. A mechanism is proposed that involves a structurally specific intermediate with extensive interaction between the protonated compound and methanol.     

Differentiation and characterization of isotopically modified silver nanoparticles in aqueous media using asymmetric-flow field flow fractionation coupled to optical detection and mass spectrometry

The principal objective of this work was to develop and demonstrate a new methodology for silver nanoparticle (AgNP) detection and characterization based on asymmetric-flow field flow fractionation (A4F) coupled on-line to multiple detectors and using stable isotopes of Ag. This analytical approach opens the door to address many relevant scientific challenges concerning the transport and fate of nanomaterials in natural systems. We show that A4F must be optimized in order to effectively fractionate AgNPs and larger colloidal Ag particles. With the optimized method one can accurately determine the size, stability and optical properties of AgNPs and their agglomerates under variable conditions. In this investigation, we couple A4F to optical absorbance (UV–vis spectrometer) and scattering detectors (static and dynamic) and to an inductively coupled plasma mass spectrometer. With this combination of detection modes it is possible to determine the mass isotopic signature of AgNPs as a function of their size and optical properties, providing specificity necessary for tracing and differentiating labeled AgNPs from their naturally occurring or anthropogenic analogs. The methodology was then applied to standard estuarine sediment by doping the suspension with a known quantity of isotopically enriched ¹⁰⁹AgNPs stabilized by natural organic matter (standard humic and fulvic acids). The mass signature of the isotopically enriched AgNPs was recorded as a function of the measured particle size. We observed that AgNPs interact with different particulate components of the sediment, and also self-associate to form agglomerates in this model estuarine system. This work should have substantial ramifications for research concerning the environmental and biological fate of AgNPs.     

大米淀粉糊化过程的光谱分析

采用衰减全反射傅立叶变换红外光谱仪跟踪测定了不同品种大米淀粉的糊化过程,同时与X-射线衍射仪测定的淀粉结晶度相对比,研究了淀粉颗粒内结晶结构在糊化过程中变化的详细情况.利用红外光谱仪计算出天然大米淀粉及其在糊化过程中各个阶段代表结晶区特征的1047cm-1和代表非晶区特征的1022cm-1两处红外吸收峰强度的比值.结果表明,天然淀粉的结晶区主要由支链淀粉侧链的双螺旋结构所形成;在加热过程中淀粉的结晶结构被破坏,并且直链淀粉含量越高,其结晶结构在糊化过程中破坏越慢,说明直链淀粉能抑制淀粉结晶结构的破坏.利用X-射线衍射仪测定了大米淀粉糊化过程各个阶段的结晶度,进一步验证了淀粉的结晶结构在糊化过程中的损失.虽然,两种测定方法对"结晶度"的定义不同,但对于淀粉结晶程度的测定具有相关性和可比性,能为研究淀粉的糊化行为提供有利的补充信息.     

Column Preconcentration of Palladium Using Phenanthrenequinonedioxime Supported on Naphthalene by Atomic Absorption Spectroscopy

Abstract

A solid chelating compound, phenanthrenequinonedioxime(PQDO) supported on naphthalene provides a rapid and economical means of preconcentration of palladium from the aqueous samples. Palladium forms a complex with PQDO supported on naphthalene in the column at pH 1.2～2.7. The metal complex and naphthalene are dissolved out from the column with 5 ml of dimethylformamide-nitric acid (100+4) and the absorbance is measured atomic absorption spectrometer at 244.7 nm. A calibration curve is linear over the concentration range 1～24 μg of palladium in 5 ml of the final solution. The sensitivity for 1% absorption is 0.126 μg/ml (0.153 μg/ml for the direct AAS method from the aqueous medium). The method has been used for the determination of palladium in various synthetic samples and can be safely applied to the environmental samples too.