Accuracy and reproducibility

Since the positions of hydrogen atoms are not well determined by X-ray analysis, they must be recalculated by some kind of geometrical canon, as described in 

on a typical lattice energy of 150 kJ mol , a change of just 0.02 A in C—H distance results in an average lattice energy difference of about 1 kJmol while stabilizations or destabilizations of up to 2-3 kJ moU for single cases are frequent. 

In carboxylic acids, extensive thermal motion or disorder over the —COOH group quite often causes the carbon-oxygen distances to vary over ranges of 1.30-1.25 and 1.25-1.20 A for the C=0 and C—O bonds, respectively. Test calculations on benzoic acid using either the observed distances of 1.275 and 1.264 A or renormalized distances of 1.30 and 1.22 A show oscillations of 1-2 kJ moU in the packing energy. 

X-ray determinations are nowadays routinely carried out at low temperature, because the resulting determination is more accurate. The effect of the temperature of the X-ray determination on calculated lattice energies has been studied by carrying out UNI calculations on variable-T crystal structures. The results are shown in Table 8.5 a 100 K change in the temperature of the crystal stracture determination brings about a variation in lattice energy from 0.1 kJmoP, for the crystal with the smallest expansion coefficient, naphthalene, to about 1 kJ mol for dinitrobenzene. 

This discussion highlights some of the many lurking variables that affect the calculation of lattice energies. Calculations can give results that differ by up to 2-5 kJ moU for a number of often-hidden reasons while this is demonstrated here for atom-atom 

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The first stage in the interpretation of a physisorption isotherm is to identify the isotherm type and hence the nature of the adsorption process(es) monolayer-multilayer adsorption, capillary condensation or micropore filling. If the isotherm exhibits low-pressure hysteresis (i.e. at p/p° < 0 4, with nitrogen at 77 K) the technique should be checked to establish the degree of accuracy and reproducibility of the measurements. In certain cases it is possible to relate the hysteresis loop to the morphology of the adsorbent (e.g. a Type B loop can be associated with slit-shaped pores or platey particles). 

Electrochemical Impedance Spectroscopy (EIS) and AC Impedance Many direct-current test techniques assess the overall corrosion process occurring at a metal surface, but treat the metal/ solution interface as if it were a pure resistor. Problems of accuracy and reproducibility frequently encountered in the application of direct-current methods have led to increasing use of electrochemical impedance spectroscopy (EIS). 

RMC can be selectively extracted into butyl acetate. Concentration coefficient 50 was achieved. Factors affecting accuracy and reproducibility of the proposed method were investigated. Method is simple and fast. Detection limit is 0,3 p.g/1 for P(V). 

The use of peroxyacids, including PMSA, makes it possible to improve photometric method of nickel determination - to increase selectivity, accuracy and reproducibility of measurements. Peroxyacids as oxidants ai e used for nickel determination in aluminium and copper alloys, natural waters, stomatological products. 

The possibility of preconcentration of selenium (IV) by coprecipitation with iron (III) hydroxide and lanthanum (III) hydroxide with subsequent determination by flame atomic absorption spectroscopy has been investigated also. The effect of nature and concentration of collector and interfering ions on precision accuracy and reproducibility of analytical signal A has been studied. Application of FefOH) as copreconcentrant leads to small relative error (less than 5%). S, is 0.1-0.2 for 5-100 p.g Se in the sample. Concentration factor is 6. The effect of concentration of hydrochloric acid on precision and accuracy of AAS determination of Se has been studied. The best results were obtained with HCl (1 1). 

This procedure was tested in the analysis of pharmaceutical products Poltava s bishofite (series Elite and Profi ) and a brine of bischofite with rusty precipitate. The data bear out the sufficient accuracy and reproducibility of the proposed procedure which allows to perform the determination magnesium, iron, copper and zinc ions at concentrations above 10 M. It was found that the content of Mg ion in the studied brine decreases in comparison with Poltava s bishofite . The Fe, Cu and Zn ions were not detected in the brine. 

Other instruments have been described that have application in the electronics field. Special metallurgical hot and cold st es are being produced, and stages capable of large motions with sub-pm accuracy and reproducibility will become common. 

The analytical techniques covered in this chapter are typically used to measure trace-level elemental or molecular contaminants or dopants on surfaces, in thin films or bulk materials, or at interfaces. Several are also capable of providing quantitative measurements of major and minor components, though other analytical techniques, such as XRF, RBS, and EPMA, are more commonly used because of their better accuracy and reproducibility. Eight of the analytical techniques covered in this chapter use mass spectrometry to detect the trace-level components, while the ninth uses optical emission. All the techniques are destructive, involving the removal of some material from the sample, but many different methods are employed to remove material and introduce it into the analyzer. 

Accuracy and reproducibility are of vital importance to industry. Quite apart from the effect of these factors on the final product, several plant items are frequently links in a continuous chain of production processes. A sizing error in one machine, for example, could overstress and damage the succeeding machinery. Similarly, an error in a press may increase stress on the tool and could necessitate an additional operation to remove excessive flash . Wear in a material preparation unit could allow oversize material to be passed to a molding machine, creating an overload situation with consequent damage. 

Apparently, the main idea behind this approach needs certain clarification. For example, formula (38) necessitates imposing a nonzero background temperature prior to the front. In spite of this fact, there are some delays in introducing new intervals, thus causing large deviations of a solution in a vicinity of the front. Formula (37) is useless for very large values of the index cr a > 20). Formula (36) has the best accuracy and reproduces rather accurately without concern of the background temperature. 

Colorimetric methods, such as those which depend upon the measurement of the color developed when excess mercury salts are added to a chloride solution, are not reproducible enough for practical purposes. They are widely used in automatic equipment, but for the purpose of maintenance and treatment of newborns, this data does not have the adequate accuracy and reproducibility. 

Polak IF, Dobkin GR, O Leary DH, Wang AM, Cutler SS. Internal carotid artery stenosis accuracy and reproducibility of color-Doppler-assisted duplex imaging. Radiology 1989 173(3) 793-798. 

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. 

Sample preparation used to extract proteins from cells prior to analysis is an important step that can have an effect on the accuracy and reproducibility of the results. Proteins isolated from bacterial cells will have co-extracted contaminants such as lipids, polysaccharides, and nucleic acids. In addition various organic salts, buffers, detergents, surfactants, and preservatives may have been added to aid in protein extraction or to retain enzymatic or biological activity of the proteins. The presence of these extraneous materials can significantly impede or affect the reproducibility of analysis if they are not removed prior to analysis. 

Eisert R, Felau L, Brown LR (2006) Methods for enhancing the accuracy and reproducibility of Congo red and thioflavin T assays. Anal Biochem 353(1) 144-146... 

Accuracy is a measure of how close the result is to the true value while reproducibility or precision is a measure of how close a series of measurements on the same sample are to each other. The accuracy and reproducibility of pH measurements can be highly variable and are dependent on several factors electrode stability (drift and hysteresis), response slope/calibration curve, and accuracy of the pH meters. While some of these factors are determined by the properties of electrodes, some measures can be taken to improve measurement accuracy and reproducibility. 

Garst, J.E., Wilson, W.C. (1984) Accurate, wide range, automated, high performance liquid chromatographic method for the estimation of octanol/water partition coefficients. II Effects of chromatographic method and procedure variables on accuracy and reproducibility of the method. J. Pharm. Sci. 73(11), 1616-1623. 

The accuracy of the thermochemical data obtained by this technique has been examined in numerous systems. In general, the data compares well, 1 kcal/mol, with that obtained by other spectroscopic and calorimetric methods. The accuracy and reproducibility of the data is dependent on the magnitude and time scale of the heat deposition detected by PAC that is associated with a given chemical process. Highly exothermic reactions are easy to detect, whereas ones that are not are difficult to detect. A thermoneutral reaction is invisible to PAC. Reactions that occur significantly slower than the response time of the transducer are not detected. Reactions that occur either slightly slower or faster than the response time are difficult to resolve accurately. Clearly, the proper choice of the transducer is extremely important in order to resolve accurately a given chemical event. 

Fig. 13.14 Demonstration of angstrom accuracy and reproducibility of the measurement of the effective fiber diameter variation, (a) measurement along the 12 mm segment with 250 pm steps, (b) measurement along the 2.5 mm segment with 50 pm steps, (b) measurement along the 250 pm segment with 5 pm steps. Solid curve first measurement, dashed curve second measurement. Reprinted from Ref. 18 with permission. 2008 Optical Society of America...

Carbon content and hydrogen content can be determined simultaneously by the method designated for coal and coke (ASTM D3178) or by the method designated for municipal solid waste (ASTM E777). However, as with any analytical method, the method chosen for the analysis may be subject to the peculiarities or character of the feedstock under investigation and should be assessed in terms of accuracy and reproducibility. There methods that are designated for elemental analysis are ... 

Wavelength accuracy and reproducibility reproducibility of sensitivity/response factors Heteroscedasticity... 

The pH measurements of the mixed contents were made immediately after taking the soil and liquid samples. The presence of a very large amount of suspended sediment affected the accuracy and reproducibility of these pH measurements. The average values for each container are summarized in Table II. The deposited pesticides, the formulating agents and the decomposition products did not change the pH from that observed for ambient water except for... 

Often, for the purpose of laboratory analysis, it is necessary to obtain a small quantity of powder from a larger batch. For maximum accuracy and reproducibility it is necessary that the sample chosen be representative of the larger initial quantity. 

Comparative results. Figure 2 in conjunction with its legend documents the excellent accuracy and reproducibility obtained over a wide spiking range, even well below the high spike quantities that have to be used with the NIOSH method in the interests of an accurate titration difference. The latter was only 0.036 ml (0.425 ml subtracted from 0.461 ml) with the 0.49 mg spike. 

Equivalency. This test compares the results of the automated procedure with the results of the validated manual method. If accuracy of the automated procedure has been proven, it may not be necessary to perform the equivalency study. However, if the manual method does not exist, then accuracy and reproducibility data should be used to assess the suitability of the automated method. The recommended testing for content uniformity, assays, degradation and impurity methods and dissolution methods are listed in Table 5.4. 

Wavelength accuracy and reproducibility, stray light, resolution, photometric accuracy and reproducibility, noise, baseline flatness, stability, and linearity... 

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