Accuracy in analysis

Maechandise H (1987) Accuracy in analysis of biological materials. Fresenius Z Anal Chem 326 613-617. 

It is difficult to cover a concentration range for kinetic systems in excess of a factor of 100 to 1000 without elaborate techniques. In the case of solutions, solubility or molar density generally limits concentrations to a maximum of about 1 mole/liter. At concentrations below 0.01 or 0.001 M it is almost impossible to achieve accuracy in analysis of better than a few per cent. Note, however, the work of Yost and Johnston and others who, by the employment of spectroscopic methods of analysis in conjunction with oscilloscope recorders, have managed to measure reactions with half-lives of 0.1 sec and less [H. S. Johnston and D. Yost, J. Chem. Phys., 17, 386 (1949) R. L. Mills and H. 8. Johnston, J. Am. Chem. Soc., 73, 938 (1951)]. 

The use labs have also been noted for their particular accuracy in analysis, including pinpointing new substances that look almost, but not quite like the old ones. They have standards for some elusive amphetamine-related.psychedelics, for example, as well as an analog of PCP which they now find frequently. USC ar PharmChem both do a lot of quantitative percentage work, thouj it is too bulky to publish in Conscientious Guide, and would not... 

Table 10.3 Example of atable used to record between-run precision and accuracy in analysis of QC samples during validation...

After the basic safety/process appreciation training, personnel are given training on analytical equipment including sampling methods (especially where new technology is involved). This training includes practice to assure repeatability and accuracy in analysis. 

Micro-mesh sieves have been applied to the determination of solid propint ingredients (Refs 17 35) and similar materials where sieve analyses are required with great accuracy in the very fine range. They are also applicable to specific problems such as the analysis of magnetic powders, and of powders consisting of mixts of substances of different specific gravities or the preparation of clearly defined particulate fractions in a short time... 

Functionalization yields have to be checked carefully by comparing the effective number average molecular weight Mn with its value calculated from the functional content of the sample, under the assumption that each macromolecule carries one function (two if a bifunctional initiator is used). Low molecular weight samples are preferred, as the functional analysis would otherwise lack accuracy. In all examples quoted high functionalization yields have been attained. 

State-of-the-art TOF-SIMS instruments feature surface sensitivities well below one ppm of a mono layer, mass resolutions well above 10,000, mass accuracies in the ppm range, and lateral and depth resolutions below 100 nm and 1 nm, respectively. They can be applied to a wide variety of materials, all kinds of sample geometries, and to both conductors and insulators without requiring any sample preparation or pretreatment. TOF-SIMS combines high lateral and depth resolution with the extreme sensitivity and variety of information supplied by mass spectrometry (all elements, isotopes, molecules). This combination makes TOF-SIMS a unique technique for surface and thin film analysis, supplying information which is inaccessible by any other surface analytical technique, for example EDX, AES, or XPS. 

In the final analysis, of greatest importance from the viewpoint of numerical analysis is the design of algorithms permitting one to obtain a solution of a differential equation on a computer with a prescribed accuracy in a finite number of operations. The user can encounter in this connection the question of the quality of an algorithm, that is, the manner in which the accuracy of the algorithm depends on... 

This chapter summarizes the computational methodologies used for conformational analysis. Specifically, Section 8.1 gives a theoretical outUne of the problem and presents details of various implementations of computer codes to perform conformational analysis. Section 8.2 describes calculations illustrative of the current accuracy in generating the conformation of a ligand when bound to proteins (the bioactive conformer) by comparisons to crystaUographically observed data. Finally, Section 8.3 concludes by presenting some practical... 

Certified value A value reported on an SRM Certificate of Analysis for which NIST has the highest confidence in its accuracy in that all known or suspected sources of bias have been fully investigated or accormted for by NIST. 

Cali JP, and Reed WP (1976) The role of the National Bureau of Standards standard reference materials in accurate trace analysis. In Lafleur PD, ed. Accuracy in Trace Analysis Sampling, Sample Handling, and Analysis, NBS Special Publication 422, Vol i pp 41-63. National Bureau of Standards, Washington, DC. 

Heydorn K (1980) Aspects of Precision and Accuracy in Neutron Activation Analysis. RIS-R-419, Roskilde, Denmark. 

Kingston HMS, Huo D, Lu Y, and Chalk S (1998) Accuracy in spedes analysis spedated isotope dilution mass spectrometry (SIDMS) exemplified by the evaluation of chromium species. Spectrochim Acta 536 299-309. 

Fairbairn HW et al. (1951) U.S. Geological Survey Bulletin 980. A cooperative investigation of precision and accuracy in chemical, spectrochemical and modal analysis of silicate rocks. 71 pp. 

This then provides a physical derivation of the finite-difference technique and shows how the solution to the differential equations can be propagated forward in time from a knowledge of the concentration profile at a series of mesh points. Algebraic derivations of the finite-difference equations can be found in most textbooks on numerical analysis. There are a variety of finite-difference approximations ranging from the fully explicit method (illustrated above) via Crank-Nicolson and other weighted implicit forward. schemes to the fully implicit backward method, which can be u.sed to solve the equations. The methods tend to increase in stability and accuracy in the order given. The difference scheme for the cylindrical geometry appropriate for a root is... 

Guidelines for acceptability of NADA and non-NADA methods are the same. For the determinative procedure, the criteria described in Method Criteria for accuracy and precision are used to evaluate data generated at participating laboratories. There are no criteria for accuracy in the analysis of the incurred residue samples however, the overall data set is reviewed to see if there is general agreement between results obtained by contract laboratories and relative to the levels reported in the sponsor s laboratory. 

WDXRF data processing with increasing accuracy of analysis (from left to right) is summarised in Figure 8.7. XRF is used to identify/quantify fillers, stabilisers,... 

To establish the well drainage boundaries and fluid flow patterns within the TFSA-waterflood pilot, an interwell chemical tracer study was conducted. Sodium thiocyanate was selected as the tracer on the basis of its low adsorption characteristics on reservoir rocks (36-38), its low and constant background concentration (0.9 mg/kg) in produced fluids and its ease and accuracy of analysis(39). On July 8, 1986, 500 lb (227 kg) of sodium thiocyanate dissolved in 500 gal (1.89 m3> of injection brine (76700 mg/kg of thiocyanate ion) were injected into Well TU-120. For the next five months, samples of produced fluids were obtained three times per week from each production well. The thiocyanate concentration in the produced brine samples were analyzed in duplicate by the standard ferric nitrate method(39) and in all cases, the precision of the thiocyanate determinations were within 0.3 mg/kg. The concentration of the ion in the produced brine returned to background levels when the sampling and analysis was concluded. 

Braithwaite RA, Brown SS. 1987. The need for accuracy in trace metal analysis A case study of childhood exposure to lead. Journal of the University of Occupational and Environmental Health 9 35-49. 

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