Reproducibility of data

In homopolymer analysis this meant a closer study of the accuracy and reproducibility of data from GPC to see how resolution correction techniques could be either circumvented or practically applied. In copolymer analysis the limitation of conventional molecular size fractionation emerged as the fundamental difficulty. An orthogonal coupling of GPCs operated so as to achieve the desired cross fractionation before detection is presented as a novel approach with considerable potential. 

Whereas precision (Section 6.5) measures the reproducibility of data from replicate analyses, the accuracy (Section 6.4) of a test estimates how accurate the data are, that is, how close the data would represent probable true values or how accurate the analytical procedure is to giving results that may be close to true values. Precision and accuracy are both measured on one or more samples selected at random for analysis from a given batch of samples. The precision of analysis is usually determined by running duplicate or replicate tests on one of the samples in a given batch of samples. It is expressed statistically as standard deviation, relative standard deviation (RSD), coefficient of variance (CV), standard error of the mean (M), and relative percent difference (RPD). 

Table 4.3. They vary with the electrode material and with the tetraalkylammonium cation used. Early workers used mercury electrodes but mercury may be involved in the overall reaction. Glassy carbon is generally favoured as the electrode material. Reproducibility of data depends critically on methods used for cleaning the glassy carbon surface [33].

Absolute accuracy has no real meaning in this experiment critical information consists of significant changes in mass loss or temperature of mass loss between samples. Inhomogeneity of samples, sample geometry, and sample size differences can have adverse effects on the reproducibility of data. 

Only a few studies [453,543-547] have been carried but on the photoelectrochemical behaviour of YBCO ceramics and single crystals. In nonaqueous media, in the absence of degradation, the data show that the usual concepts of photoelectrochemistry of p-type semiconductors apply to those systems. Such studies have not yet been actively developed, probably because of the high sensitivity of photoelectrochemical processes to the nature of materials. Reproducibility of data for such complex systems as HTSC oxides is an issue. At the same time, the photoassisted electrochemical processes on HTSC electrodes can lay the basis for certain effective technologies. This is especially true for the photoelectrochemical etching and metallization which prove to be extremely effective as applied to semiconductors [503,504]. 

Although we have access to an enormous amount of information, the quality and reproducibility of data varies considerably. Governmental and regulatory influences have not provided any guarantees as to the accuracy of data related to xenobiotics and the researcher needs to understand the purpose and mandates behind an information resource to fully evaluate the data contained within. For example, the National Institute for Occupational Safety and Health (NIOSH) Registry of Toxic Effects of Chemical Substances (RTECS) criteria for selection of data is not based on the reproducibility of that data. Other sources, such as the National Library of Medicine s Hazardous Substances Databank (HSDB), present information compiled from a wide variety of source materials that are extensively reviewed by experts. 

Methods. Using an Agla microsyringe, alkyl alcohol solution (0.025 ml) was spread on the subsolution of 0.01 M HC1. A time interval of 5 minutes was allowed for spreading solvents to evaporate or diffuse in the subsolution from the monolayers. The monolayer was compressed at a constant rate by an electrically operated motor. The surface pressure area curve for a monolayer was recorded automatically by x-y recorder. Three to five mono-layers of each mixture were studied and the results reported are average values. The reproducibility of data was + 0.15 8 /molecule. The detailed discussion of the apparatus is given elsewhere (17). 

In Table II the results are presented of investigations conducted in the United Kingdom [2] and the United States [15. 21] to compare the data for azide ion content of various commercial azides as determined by the above four methods. Different samples were used for each of the investigations, and thus it is not possible to make direct comparison with respect to the reproducibility of data from investigation to investigation. Despite the precise results, manipulation of azides in acid solution is always subject to error through possible loss of hydrazoic acid it is preferable to work in neutral solution. 

To develop the most cost efficient proeess, scale-up data must be collected by repeating experiments at the bench and pilot scale level. These data must be extensive. Unfortunately, the collection is far more difficult than it would be in the chemical and petrochemical industries. The nature of working with living material makes contamination commonplace and reproducibility of data difficult to achieve. Such problems quickly distort the relevant scale-up factors. 

In general, a satisfying method for quantitative analysis has to provide high sensitivity, low limits of detection (LOD), low limits of quantification (LOQ), a linearity range of at least three to four orders of magnitude, high precision (repeatability and reproducibility of data), and accuracy (experimental data as close as possible to the true value ). 

Further studies in this direction [79, 80] suggested the following possible causes of poor reproducibility of data and systematic errors (1) the presence of residual solvent in the test sample (2) the wide range of pyrolysis temperatures (3) contamination of the equipment by sample residues and residual products of previous pyrolyses and (4) widely differing sample sizes. To obtain reproducible results one should give equal attention to all stages sample preparation, pyrolysis and GC analysis. 

The Mossbauer effect has given useful information in the study of chemical reactions which involve surface states and chemisorption. Reproducibility of data and their interpretation are difficult in this type of work because the adsorbing material may be affected by its pre-history. Comparisons have to be made with iron cations in compounds of known site symmetry. 

For DVS experiments, the sample was placed into a glass pan and the vapour concentration was stepped up by 2.5% increments until 40%, 5% until 70% and 10% until 90%. Hexane and Dichloromethane have been used as probe molecules. The measurements were carried out at 25 C and two adsorption and desorption cycles have been recorded to check for hysteresis and reproducibility of data. Nitrogen was used as a carrier gas. Samples were equilibrated in-situ for 30 min in a pure gas stream prior to the experiment. 

This review of physical, bulk chemical, surface chemical, and spectroscopic techniques for the characterization of powders shows that no one or two techniques can provide all the necessary details regarding powder properties. In fact, each method reveals a distinctly different characteristic of the powder. Often, a choice must be made in terms of the selection and measurement of relevant properties of a powder. When one is faced with this question of which specific properties to measure, the relationships between powder properties and their effect on the final microstructure and properties of the ceramic should be explored. Currently, the quality and reproducibility of data are significantly affected by the unavailability of standard methods and standard reference materials. Efforts are underway in different organizations around the world to alleviate this problem. 

More and more physical data on ILs and their properties are being collected. For some measurements there are even multiple values. But there is a need for the reproducibility of data to be tested in several laboratories as well as an ever-growing list of ILs on which to collect data. At this early stage it is possible to draw some tentative general conclusions. 

Inasmuch as gas analysis was made continuously during a run, it was not considered necessary to rerun each experimental point several times. Instead, 50% of the points were rerun at different flow rates, in order to check attainment of equilibrium and reproducibility of data, to compare gas analysis of different analyzer cell lengths, and particularly to test the ability of the equilibrium cell to retain all solid particles. The results of all check runs agreed with the original data within the limits of gas analysis accuracy, thus indicating that the equilibrium cell was effective in retaining the solid particles. 

It is difficult to decide which of the criteria listed earlier for selection of an internal standard element is most important however, the rate of volatilization certainly is one of the more important. If the distillation rates of the internal standard and the analysis element differ greatly, the reproducibility of data will be adversely affected. If one element appears in the arc soon after the arc is ignited and the other appears later, the arc temperature will differ and variations in electrode spacing, arc current, and arc wandering will occur. Figure 8-2 illustrates volatilization rates of some selected elements. 

Prior to, during, and after fabrication of the reactor vessel, nondestructive tests based upon Section III of the ASME Boiler and Pressure Vessel Code are performed on all welds and forgings as indicated. The nondestructive examination requirements including calibration methods, instrumentation, sensitivity, reproducibility of data, and acceptance standards are in accordance with requirements of the ASME B PV Code, Section III. (See Table 5.2-1). These methods, procedures and requirements are compatible with Section XI of the ASME Code so that results of preservice inspections can be correlated with in-service inspections. Strict quality control is maintained in critical areas such as calibration of test instruments. 

Answer by author Initially in the determination of the 76°K pure methane isotherm, reactivation conditions were varied from room temperature and no evacuation to 250°F with evacuation for 24 hours with no noticeable effect on the reproducibility of data points. The authors feel that this maximum reactivation temperature is not high enough to affect a significant change in the surface of the adsorbent. Furthermore, the same effect of temperature on the adsorption of methane was observed in two separate sets of experiments. 

Particularly with derivative methods, great demands are made upon storage when a high reproducibility of data and a low noise level are sought, because rapid alteration of the y values with respect to the x values (that is, a steep rise of the curve) becomes... 

Torsional pendulums designed for adsorption measurements of gases on solids are not available commercially today. Also principles for optimal design aiming at high sensitivity and reproducibility of data have not yet been formulated though hints for this are given in [5.2, 5.7]. 

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