In modern materials science the characterisation of nanostructures is becoming increasingly important. For measurement of the quality of nanoscale multilayer arrangement with high spatial resolution a method is described that is based on the broadening of the spots in the Fourier transformation of transmission electron microscopic images of multilayer cross-sections. Using this method on Si/Ge superlattices with periodic lengths between 4 and 12 nm it could be quantitatively shown that the layer perfection decreases with increasing periodic length. The transition from elastic to plastic deformation between the Si and Ge layers at larger periodic lengths can be the reason for this behaviour. 相似文献
The National Analytical Reference Laboratory of the Australian Government Analytical Laboratories was initially accredited to ILAC Guide G 12:2000 in January 2000 and is currently accredited to ISO Guide 34 (2000) for the production of a range of pure organic substance reference materials. This paper discusses the practical challenges and rewards of developing and implementing a quality system for reference material production and discusses some of the barriers, and potential solutions, to more general implementation of third-party accreditation. 相似文献
Every analytical result should be expressed with some indication of its quality. The uncertainty as defined by Eurachem ("parameter
associated with the result of a measurement that characterises the dispersion of the values that could reasonably be attributed
to the, . . ., quantity subjected to measurement") is a good tool to accomplish this goal in quantitative analysis. Eurachem
has produced a guide to the estimation of the uncertainty attached to an analytical result. Indeed, the estimation of the
total uncertainty by using uncertainty propagation laws is components-dependent. The estimation of some of those components
is based on subjective criteria. The identification of the uncertainty sources and of their importance, for the same method,
can vary from analyst to analyst. It is important to develop tools which will support each choice and approximation. In this
work, the comparison of an estimated uncertainty with an experimentally assessed one, through a variance test, is performed.
This approach is applied to the determination by atomic absorption of manganese in digested samples of lettuce leaves. The
total uncertainty estimation is calculated assuming 100% digestion efficiency with negligible uncertainty. This assumption
was tested.
Received: 3 November 1997 · Accepted: 2 January 1998 相似文献
Since the 1980s, quality systems have become an essential element in successful companies and institutions. Today those systems are indispensable to fulfill the needs of the customers and last but not least the requirements of the society. Depending on the company's activities and fields of services, it is necessary to establish various quality systems. The Institut Fresenius (IF) Group runs a number of analytical laboratories and sampling groups. The whole group was accredited according to DIN EN 45001 in 1994. Good Laboratory Practice (GLP) was introduced in 1992 and was certified by the national authority. For certain customers, IF Group is also obliged to work according DIN EN ISO 9001 or GMP. A comparison of these systems with respect to their different priorities shows the possibility of integrating their rules into one comprehensive quality system. The IF Group has therefore installed a quality system operating in parallel. Multilocation accreditations and/or certifications are taking these efforts into account. The benefits are: high transparency of the system for the customers, auditors and personnel, a reduction of maintenance costs, and great flexibility to react to new standards. Could these activities lead to a new Integrated Management System? 相似文献
Ion-exchange resins have been often used as catalysts especially those based on styrene-divinylbenzene copolymers with sulfonic acid groups in the aromatic rings of polymer chains. That is due to the advantages of heterogenous catalysis over the homogeneous acid catalysis. Moreover, resin catalysts can often lead to high selectivity in organic reactions due to the matrix effects. Therefore, the study of copolymers synthesis conditions to determine the type of polymer structure produced as well as the characterization of sulfonic resins obtained thereof are of great interest. The current paper describes the synthesis, characterization and evaluation as catalysts of sulfonic resins derived from polymer supports synthesized by aqueous suspension polymerization of styrene and divinylbenzene. The reaction conditions were varied and polymer supports with different physical properties and morphological characteristics were obtained. The polymer supports were chemically modified by sulfonation. The resultant sulfonic resins had their catalyst activity evaluated in the esterification of acetic acid with n-butanol. 相似文献
Pan, H. and Han, S., 1993. New forms of McKay-Perring equations for mixed electrolyte solutions. Fluid Phase Equilibria, 90: 289-306.
A rigorous derivation is given for new forms of the McKay-Perring equations and the partial differential equation relating the activity coefficients of two electrolytes in mixed electrolyte solutions. They all have simple and symmetrical forms when the independent variables are the total ionic concentration and the fraction of ionic concentration. However, the simple and symmetrical forms remain only when the electrolytes are of the same charge types and when the independent variables are ionic strength and the fraction of ionic strength. The method of surface fitting is introduced to evaluate the McKay-Perring equations. The calculated results for four systems are in good agreement with those from the Pitzer equations. 相似文献
Summary To measure the five classical protein fractions in human serum several electrophoretic techniques are available. Besides separation
on cellulose acetate membrane or agarose gel, capillary zone electrophoresis (CZE) may be a useful analytical alternative
in clinical routine. We have compared the Dionex CES I capillary electrophoresis system with that of the Olympus Fractoscan
using specimens submitted for routine analysis. For clinical evaluation 102 samples from patients with various diseases have
been analysed. Serum protein fractions were judged on separation performance, precision and the regression method ofBablok-Passing. Regression analysis revealed variable agreement between both methods with a slope ± intercept of 2.10–0.52 (α1-fraction) and 1.0–0.20 (α2-fraction) as worse and best, resectively; and the coefficient of variation of migration time: 5.9 %–6.8 % (between-run imprecision).
Differences in the comparison of fractions are mainly caused by the improved resolution of CZE; e.g. one β-globulin peak on
cellulose acetate is separated into two distinct protein fractions in CZE, including more detailed diagnostic information—as
is also the case with γ-fraction. In some cases monoclonal gammopathy with low concentrations of immunglobulin clone can only
be detected in CZE, whereas the cellulose acetate membrane (CAME) electropherogram is inconspicuous. The within-run precision
(N=18) gave coefficients of variation of peak areas 1.3–5.9 % (CZE) and 1.0–3.8 % (cellulose acetate membrane). This is the
first time that a complete clinical evaluation of CZE serum protein fraction analysis has been performed. CZE with its higher
resolution and hence more detailed diagnostic information in some cases, showed good separation patterns, precision and correlation.
Interchangeability of results showed that this CZE method is well suited for analysis of serum protein fractions in clinical
routine.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996. 相似文献