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1.
An improved automated continuous sample introduction system for microfluidic capillary electrophoresis (CE) is described. A sample plate was designed into gear-shaped and was fixed onto the shaft of a step motor. Twenty slotted reservoirs for containing samples and working electrolytes were fabricated on the “gear tooth” of the plate. A single 7.5-cm long Teflon AF-coated silica capillary serves as separation channel, sampling probe, as well as liquid-core waveguide (LCW) for light transmission. Platinum layer deposited on the capillary tip serves as the electrode. Automated continuous sample introduction was achieved by scanning the capillary tip through the slots of reservoirs. The sample was introduced into capillary and separated immediately in the capillary with only about 2-nL gross sample consumption. The laser-induced fluorescence (LIF) method with LCW technique was used for detecting fluorescein isothiocyanate (FITC)-labeled amino acids. With electric-field strength of 320 V/cm for injection and separation, and 1.0-s sample injection time, a mixture of FITC-labeled arginine and leucine was separated with a throughput of 60/h and a carryover of 2.7%.  相似文献   

2.
Summary Thermal field-flow fractionation separates polymers with high selectivity according to their Soret coefficient,S τ, hence, according to their molar mass, and therefore consitutes an efficeint physicochemical tool for the determination of the Soret coefficient of a given polymer in the carrier liquid from its retention time. However, the polymer concentration in the sample influences the retention time and, hence, the value ofS τ derived from it. An experimental study of the influence of sample concentration on retention,S τ, and peak shape was performed for the polystyrene-decalin system over a relatively large temperature domain and for various molar masses. It is found that the retention time and the value ofS τ increase with increasing sample concentration, the more so as the cold wall temperature is lower. This appears to be in contradiction with the general non-equilibrium thermodynamic expression derived for polymer-solvent systems with positive second virial coefficients, such as the present system over the temperature range investigated. There seems to be a temperature for which the dependence ofS τ on sample concentration vanishes. This temperature is about 375 K for the polystyrene-decalin system. As the sample concentration increases, the peak barycentre and the standard deviation increases. As the peaks are fronting, the skewness is negative and becomes more negative as the sample concentration increases. The peak skewness appears to be a good indicator of the onset of sample concentration effects. The threshold concentration, for which these effects begin to become significant, decreases with increasing molar mass.  相似文献   

3.
Stability and reproducibility of gel-suspension samples were investigated in order to evaluate the characteristic feature of the gel-suspension method for14C activity measurement. Commercially available gelling agent, N-lauroyl-L-glutamic-α,γ-dibutylamide, was used for the gelformatio of the samples. No change of the counting rate for the gel-suspension sample was observed for more than 2 years after the sample preparation. Four samples used for checking the reproducibility of the sample preparation method. The same values were obtained for the counting rate of14C activity within the counting error. No change of the counting rate was observed for the “re-gelated” sample. These results show that the gel-suspension method is appropriate for the14C activity measurement by the liquid scintillation method and is useful for a long-term preservation of the sample for repeated measurement.  相似文献   

4.
In this study, we compare near-infrared (NIR) and Raman spectroscopy for the determination of the density of linear low density polyethylene (PE) (in a pellet form). As generally known, Raman spectral features are more selective than those of NIR for most chemical samples. NIR spectroscopy has been more extensively used for the quantitative analysis of polymers, but Raman spectroscopy is the better choice as long as the problem of reproducibility of Raman measurements (especially for solid samples), mostly resulting from insufficient sample representation due to probing only localized chemical information and the sensitivity of sample placement with regard to the focal plane, can be overcome. To improve sample representation and reproducibility of Raman measurements, we have employed the wide area illumination (WAI) Raman scheme, capable of illuminating a laser onto a large sample area (28.3 mm2) for Raman spectral collection (a 6-mm laser spot with a focal length of 248 mm). Diffuse reflectance NIR spectra of PE pellets were collected using a sample moving system which allowed for the scanning of large areas. The prediction error was 0.0008 g cm−3 for Raman spectroscopy and 0.0011 g cm−3 for NIR spectroscopy. The harmonization of inherently selective Raman features and a reproducible spectral collection with correct sample representations using the WAI scheme led to an accurate determination of the density of the PE pellets.  相似文献   

5.
In x‐ray photoelectron spectroscopy (XPS) the Auger parameter is often used to study the electronic properties of elements, particularly in insulator materials, because this parameter is assumed to be independent of charging effects. In this paper we report on subtle differences in sample structure and experimental conditions for which the sample potential may not remain constant during the measurements for some spectrometers or experimental arrangements; for such conditions the Auger parameter is not independent of charging. We compare a series of measurements with insulating plate substrates of Al2O3 on which different amounts of SnO2 and Au were deposited. X‐ray photoelectron spectra were collected for different conditions of the sample that was placed either grounded or left floating on a metallic sample holder during measurement. It is found that the Auger parameter is independent of the experimental conditions for Au but substantial differences were found for deposited SnO2. Surprisingly, measurement artifacts due to charging appeared in the Auger parameter for Sn when the sample holder was grounded but not when it was left floating. In the grounded samples differences up to 0.6 eV in the Auger parameter for Sn were found with respect to the actual value of this parameter measured with substrates where charging effects were not significant. Because no differences in peak broadening have been observed under different measurement conditions, it has been assumed that the shift was not caused by a conventional differential charging phenomenon. Considering the different response of the substrate and the deposited layer on stabilizing the charge when the sample is grounded, we have worked out a possible explanation to account for the observed artifacts. Instrumental specifications should be optimized very carefully, especially if (as here) relatively high charging shifts point to a non‐optimum self‐biasing of the surface potential at the insulating samples. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

6.
Chemical analysis is a multi-stage process, which starts with primary sampling and ends with evaluation of the resuts. Especially in trace analysis and microanalysis of solid materials, sampling can far outweigh all other sources of error. For estimating the reliability of complete analytical procedures, a method is needed which can be used to estimate the errors made in the primary and the secondary sampling and sample preparation steps. Based on Gy's theory of sampling, a computer program (SAMPEX) was written for the solution of practical sampling problems. The method involves the estimation of the sampling constant, C. For well-characterized materials, C can be estimated from the material properties. If the necessary material properties are difficult to estimate, C can be evaluated experimentally. The program can be used to solve the following problems: minimum sample size for a tolerated relative standard deviation of the fundamental sampling error; relative size for a tolerated for a given sample size; maximum particle size of the material for a specified standard deviation and sample size; balanced design of a multi-stage sampling and sample-reduction process; and sampling for particle size determination.  相似文献   

7.
A simple and new flow-injection manifold (CUDS) for the continuous ultrasound assisted dissolution of a soluble solid sample coupled to a flow-injection flame atomic absorption spectrometric manifold for the continuous iron determination is described. An experimental design was used for the evaluation of factors involving the CUDS. The method was applied to a certified reference material (CRM-151, skim milk powder) for quality assurance/validation and to real samples (milk powder and infant formulas). The total sampling frequency achieved was 80 samples per hour with a relative standard deviation for the complete procedure of 1.1%. The detection limit was 0.60 μg g−1 for a sample amount of 30 mg. The results demonstrated that the CUDS is an innovative and efficient tool as compared to the manual-traditional sample preparation methods, but with drastic increase of both sample throughput and precision.  相似文献   

8.
Monitoring metabolite uptake and excretion in the culture medium is a noninvasive technique that is used for the metabolic study of cleaving embryos after in vitro fertilization. Low sample consumption, the versatility of the detection, and optimal sensitivity and selectivity are essential elements for extracellular metabolome analyses, and can be conveniently achieved by combining CE with mass spectrometric detection. This paper reports a method for amino acid determination in a limited volume sample (8 μL) of spent culture media collected after the cultivation of in vitro fertilized embryos. Special attention was focused on the sample preparation procedure. The sample was processed with acetonitrile, which facilitates online sample preconcentration via field-amplified sample stacking, and undesired sample evaporation was significantly reduced by the simultaneous addition of dimethyl sulfoxide. Key parameters that affected electrophoretic separation and mass spectrometric detection were investigated, including the type of buffers and organic solvent, optimization of their concentrations, and finally the settings for their ionization. The separation and quantification of 19 amino acids were achieved using 15% acetic acid as the background electrolyte with a sheath liquid consisting of an equimolar mixture of methanol and water. The applicability of the optimized system was demonstrated by determining the amino acid profile in 40 samples of spent cultivation medium in this pilot study. This developed method also has great potential for amino acid analyses in minute sample volumes of other biological matrices.  相似文献   

9.
In this study a procedure for sample digestion based on sample combustion assisted by microwave radiation is proposed. Combustion is started by microwave radiation in the presence of oxygen under pressure using ammonium nitrate as aid for ignition. The system was adapted in a microwave oven with quartz closed vessels. A quartz piece is used simultaneously as a sample holder and as protection to the cap of quartz vessel from the flame generated in the combustion process. Sample was pressed into a pellet and placed on a disc paper in the holder and 50 μl of 50% m/v ammonium nitrate solution was added. The influence of the absorption solution (diluted and concentrated nitric acid or water) on the recoveries for Cu and Zn was evaluated. About 3 s of microwave irradiation was necessary to start the combustion. The combustion process was evaluated in relation to the influence of sample mass on the ignition time, combustion time and maximum operation pressure. Bovine liver, milk powder and oyster tissue certified reference materials were used to evaluate the accuracy of the procedure for determination of copper and zinc. Good agreement for zinc (96% to 103%) was obtained from bovine liver certified reference material when microwave combustion and microwave combustion followed by reflux were used to sample decomposition, even if water was used for absorption of analyte. For copper, the combustion followed by reflux of 5 min allows an agreement from 96% to 100%. Similar results were obtained for oyster tissue samples. However, for milk powder good agreement close to 100% was obtained only if 4 mol l− 1 HNO3 was used with a reflux step. Results from the proposed procedure were also compared to those from conventionally used procedures for biological samples decomposition, such as wet digestion in open vessels and microwave-assisted digestion in closed vessels. The advantages of this procedure include the complete sample decomposition in less time than other procedures and the acid consumption was always lower than 2%. Another advantage is the low residual carbon content, less of 1.4% without reflux and less than 0.3% with the reflux step and the possibility of use of diluted acid as absorbing solution. Moreover, the new holder allows an effective protection of the vessel cap to burnt high masses.  相似文献   

10.
Absence of gradients and Nernstian equilibrium stripping (AGNES) is a recently developed electroanalytical technique specifically designed for the direct determination of free concentrations of metal ions. AGNES is applied here to the determination of free Zn concentration in a river water sample. The method has been validated with synthetic solutions of low ionic strengths containing Zn and 2,6-pyridinedicarboxylic acid and then applied to synthetic river waters and to a natural sample collected from Besòs River in Montcada i Reixac (Catalonia, North-Eastern Spain). In the river sample, an average free Zn concentration of 12.8(4) nM was obtained, while the total dissolved Zn concentration was 0.51(8)?μM. To control and maintain pH and pCO2 constant during AGNES measurements, a novel device for N2/CO2 mixed purging has been developed.  相似文献   

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