Computer simulation of the uncertainty of analytical results

Uncertainty is an important quality parameter of any analytical result. Estimating the uncertainty of analytical procedures can be rather difficult in many instances. Computer simulation based on multiple repetition of calculation of the resulting quantity while varying slightly the input parameters is an alternative option. The input parameters for the various computation runs are composed of two terms: the constant mean value and the error, obtained as the product of the standard uncertainty of the parameter in question and a random number with the normal distribution N(0.1). This approach can also serve to optimize measuring procedures, as demonstrated on an example of the determination of lead in biological materials by isotope dilution mass spectrometry. The accuracy of the optimized method was tested by analysis of some CRMs, the robustness of the method was examined, and the detection limit (10 ng/g Pb) and repeatability (4 ng/g Pb) were determined. Received: 30 September 1998 / Revised: 3 December 1998 / Accepted: 8 December 1998     

Attrition of dolomitic lime in a fluidized-bed reactor at high temperatures

Results of an experimental study on the rate of attrition of lime catalyst/sorbent in a high-temperature, turbulent fluidized bed with quartz sand are presented. Batch measurements were conducted at 850°C in an electrically heated gasification reactor of the inner diameter of 5.1 cm with three samples of high-grade dolomitic lime of the particle size 450 ??m, 715 ??m, and 1060 ??m, respectively. In addition to the influence of the particle size, the effect of operating (elapsed) time was investigated at different superficial gas velocities. Assuming that the attrition rate decreases exponentially with time, a simple mechanistic model, enabling the correlation of the measured experimental data, was developed. The course of the lime particles attrition is described as a function of the elapsed time, excess gas velocity, and particle size. The presented approach and the results might be applicable for the attrition of high-grade dolomitic lime, particularly in fluidized gasification of biomass.     

Analysis of antiepileptic drugs by capillary gas chromatography with on-column injection

A simple and quick gas chromatographic method has been developed for the determination of up to six commonly used antiepileptic drugs in human serum. The antiepileptics are isolated from serum by solid phase extraction on to a reversed phase sorbent and recovered with ethyl acetate as eluent. The ethyl acetate eluate is suitable for direct on-column injection on to a phenyl methyl siloxane capillary column; hydrogen is used as carrier gas and the compounds are separated with a two-ramp temperature program. Detection is by FID. The reproducibility of the method varies between 2 and 6% RSD, depending on the drug and the level analyzed; limits of detection were found to be 14–51 pg and minimum assayed concentrations in serum were between 14 and 51 ng/ml.     

Separation of microamounts of yttrium from strontium in the two‐phase water/nitrobenzene system

A rapid and very effective separation of carrierfree 90 Y in the aqueous phase of the water/nitrobenzene system from an 90 Y/90 Sr generator is proposed. After a twostage extraction separation, the radionuclide impurity of 90 Sr in the final aqueous phase containing carrierfree 90 Y is approximately 10 16%, while the chemical yield of 90 Y in this phase is practically 100%.     

Synthesis, Properties, and Reactions of 5-Substituted Derivatives of 2,3-Diphenylquinoxaline [1]

Catalytic hydrogenation of 5-nitro-2,3-diphenylquinoxaline led to the corresponding amine which, in turn, afforded products of nucleophilic substitution on reaction with alkoxymethylene derivatives. Thermal cyclization of selected alkoxymethylene derivatives yielded substituted pyridoquinoxalines. The conditions for successful hydrolysis of ester, decarboxylation of the acid, following chlorination of pyridone and reductive removal of the chlorine atom from it to produce parental heterocycle 2,3-diphenyl-pyrido[2,3-f]quinoxaline were found. All of the tested products of the nucleophilic substitution showed no antibacterial activity.     

Uncertainty of determination of palladium in road dust sample by inductively coupled plasma mass spectrometry

The determination of palladium in a road dust sample taken close to the highway (w _Pd=450 ng g⁻¹) was carried out by the ICP-MS method after sample decomposition by aqua-regia. Analyses were evaluated by two methods: external calibration accompanied with mathematical correction of spectral interferences (EC) and isotope dilution measurement after separation of Pd by extraction to dibutyl sulfide solution (ID). In both cases, the uncertainties and accuracy of results were investigated. Although in the case of ideally homogeneous sample the repeatability of EC results (11 ng g⁻¹ Pd) was somewhat lower than those of ID results (16 ng g⁻¹ Pd), the uncertainties of results of both techniques were almost the same and they reached the level of 19 ng g⁻¹ Pd. The main uncertainty source of the EC method is represented by the correction of spectral interferences. In case of real non-homogeneous sample, the main uncertainty component represents the soil sampling. The uncertainty of results (approx. 75 ng g⁻¹ Pd) only slightly exceeded the repeatability (approx. 70 ng g⁻¹ Pd). The accuracy of results was proven by analyses of CRM TDB–1 Diabas Rock (in case of ID) and by the standard addition method (in case of EC).     

On the convergence of a combined finite volume-finite element method for nonlinear convection-diffusion problems

We present the convergence analysis of an efficient numerical method for the solution of an initial-boundary value problem for a scalar nonlinear conservation law equation with a diffusion term. Nonlinear convective terms are approximated with the aid of a monotone finite volume scheme considered over the finite volume mesh dual to a triangular grid, whereas the diffusion term is discretized by piecewise linear conforming triangular elements. Under the assumption that the triangulations are of weakly acute type, with the aid of the discrete maximum principle, a priori estimates, and some compactness arguments based on the use of the Fourier transform with respect to time, the convergence of the approximate solutions to the exact solution is proved, provided that the mesh size tends to zero. © 1997 John Wiley & Sons, Inc.