Concentration precision

Prindle and Ray (ZB.) have recently analyzed the same styrene data using a hybrid model consisting of the micellar nucleation mechanism above the CMC and of the homogeneous nucleation and coagulation mechanism below the CMC. Their simulations show a much steeper rise in the particle number concentration precisely at the CMC than predicted by EPM. Their hybrid model does not appear to predict that the particle concentration levels off at high surfactant concentrations. 

The recovery of different concentrations of detergents added to seawater was used to evaluate the accuracy of the method. The recovery is 80% at 1 xg/l but reaches 90% at 10 ig/l. The recovery is 97% or better at higher concentrations. Precision was very good. 

Method Equipment Sample form Quantitative Concentration Precision... 

In the first studies of detonation the efforts of scientists were directed toward proving general agreement between the calculated and measured values of the detonation velocity. Later, interest was concentrated precisely on the small differences between the calculated and measured values of the velocity. This interest was based on the idea that the lag of the measured value from the calculated one was due to the fact that part of the reaction energy did not have time to be released in the wave and was released somewhere later, no longer influencing the detonation velocity. 

Investigation of the degradative effects of ozone on elastomeric materials has necessitated developing techniques to measure ozone concentration precisely. The literature ( 4, 7, 9, 10, 13) has presented tJie efforts of several workers. However, the techniques used costly equipment such as infrared and ultraviolet spectrophotometers, aqueous colorimetric methods involving the formation or destruction of fluorescence or dyes, and iodometric procedures. 

CAD was found to be superior to both UV and ELSD. CAD generated nearly uniform responses and showed the best accuracy and LOD in comparison to the other two detection methods. At higher concentrations, precision was similar to UV, while UV detection showed better precision at lower concentrations than did CAD or ELSD. The LOD of CAD was up to two five times higher for the compounds investigated than that of ELSD. 

The maximum in this curve, first observed by Norton and Lewis (1963), is similar to the one found in the Zr-C system. Later measurements of density by these authors show that it is not caused by a variable metal vacancy concentration. Precision density measurements by Storms (1966b) support this conclusion and place the number of metal atom vacancies at less than 0.5% of the total metal positions. In addition, Gorbunov et al. (1961), using neutron diffraction, found the carbon atoms statistically distributed in the octahedral voids and all the metal positions filled by Ti atoms. 

It is of course of interest to determine which of the methods of quantitation provides the most accurate and precise quantitative data. It is equally important to consider the constant trade-off for precision and sensitivity. At very low concentrations, precision often becomes limited by extraneous factors, such as wall effects. In such cases, high-precision measurements are becoming virtually unobtainable. In analogy to the Quantitative Ingredient Declarations (QUID) in food analysis, which require statements as to the uncertainty of the measurement and the variability of the results (sampling ), also for industrial polymer analysis intra- and interlaboratory variation and the meaning of average analytical results needs to be established. It is the responsibility of the analyst to adequately describe the instrumentation and performance to duplicate the repeatability and accuracy of the developed method. 

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