Spectrophotometric data evaluation

Long, J. R. Drago, R. S. The Rigorous Evaluation of Spectrophotometric Data to Obtain an Equilibrium Constant, /. Chem. Educ. 1982, 59, 1037-1039. 

In addition to designing experiments to avoid the above complications, caution should be exercised in the work up of the data. The procedure we recommend for evaluating spectrophotometric data has been reported (26, 27). An improved method for selecting the best K i was subsequently reported (20). Adaptation of these equations to calorimetric (20) and magnetic resonance (23) experiments have also been reported. For the spectrophotometric experiment in which there is an overlap of the absorption band of the acid and the adduct it forms, the equation has the form ... 

In an optical study of sugar products in solution, it is essential to differentiate between the color, the spectrophotometric data, and the evaluation of the colorant. The term color should be reserved solely as an expression of visual appearance. In addition, a uniform nomenclature for spectrophotometric data should be adopted by the sugar industry. 

The spectrophotometric data were first used to evaluate the number of species formed in the system and it was found that four significant components were needed to reproduce the data. 

Finally, the spectrophotometric data were analysed under the same assumption in order to obtain the absorption spectra of the different species and their distribution as a function of the mean composition of the solution. The result of this analysis was found to be in good agreement with the evaluation from the redox-potential data. 

Based on spectrophotometric data, Battaglia and Miller (5) evaluated the constant K at pH 3.9 and 22 °C, where... 

General discussion. In a spectrophotometric titration the end point is evaluated from data on the absorbance of the solution. For monochromatic light passing through a solution, Beer s Law may be written as ... 

Objective Evaluation of Color. In recent years a method has been devised and internationally adopted (International Commission on Illumination, I.C.I.) that makes possible objective specification of color in terms of equivalent stimuli. It provides a common language for description of the color of an object illuminated by a standard illuminant and viewed by a standard observer (H). Reflectance spectro-photometric curves, such as those described above, provide the necessary data. The results are expressed in one of two systems the tristimulus system in which the equivalent stimulus is a mixture of three standard primaries, or the heterogeneous-homogeneous system in which the equivalent stimulus is a mixture of light from a standard heterogeneous illuminant and a pure spectrum color (dominant wave-length-purity system). These systems provide a means of expressing the objective time-constant spectrophotometric results in numerical form, more suitable for tabulation and correlation studies. In the application to food work, the necessary experimental data have been obtained with spectrophotometers or certain photoelectric colorimeters. 

Neither visible nor spectrophotometric evidence has ever been secured to indicate that any of the dye is transferred to the petroleum ether. If, however, for other reasons it is deemed undesirable to extract oils and waxes at this stage, the extraction may be performed similarly just prior to the addition of the sodium nitrite solution. Extraction at this earlier stage is best accomplished with 30° to 60° C. petroleum ether, for the 60° to 70° C. fraction will remove significant amounts of the reduced parathion hydrochloride. This point is illustrated by the data in Table V. In each instance, 194 micrograms of the reduced amine in 43 ml. of water at pH 3.1 were extracted twice with 5-ml. portions of the petroleum ether, then color development and evaluation were carried out in the usual manner. 

Alcock, R. M. Hartley, F. R. Rogers, D. E., A damped non-linear least-squares computer program (dalsfek) for the evaluation of equilibrium constants from spectrophotometric and potentiometric data, J. Chem. Soc. Dalton Trans. 115-123 (1978). 

The limitations of the Gutzeit method for determining arsenic are well-known. The spectrophotometric molybdenum blue or silver diethyldithio-carbamate procedures tend to suffer from poor precision. Sandhu [34] has described a spectrophotometric method for the direct determination of hydrochloric acid-releasable inorganic arsenic in soils and sediments. The method provides reliable data on the quantitative recovery of 2.0 xg of arsenic(V) added to 5.0 g (0.4 mg/kg) of soil, clay, sand and sediment samples. The method is simple, reliable and relatively rapid 24 samples can be analysed in about an hour. It does not require elaborate equipment and can be routinely used for the quantitative determination of arsenic in soil and soil-like material. The detection limit has been established as 0.5 xg of arsenic. The extent of ionic interference when this method is used for arsenic determination in soil was also quantitatively evaluated. 

The following table is provided to aid in the use of applications of ultraviolet spectrophotometric detectors. The data here are used to evaluate the potential of detection of individual chromophoric moities on analytes.1-3... 

Table 1. The effect of 1 mM NaF + 20 pM A1C13 on the acetylcholinesterase activity (AChE) in freshly prepared intact RBC and in hemolysate of patients with AD (mean age 72.5 5.1 years), age-matched healthy controls (AM-HS) (72.1 1.6 years), and the group of young healthy subjects (YS) (35.9 8.5 years). Whole venous blood samples were drawn from each subject after overnight fasting., always at 07 30 AM. Red blood cells (RBC) were isolated from the blood of patients with AD, AM-HS, and YS by centrifugation [68], RBC AChE activity was evaluated in intact freshly prepared RBC or hemolyzate following the spectrophotometric method [45] with modifications. Buffer was Tris-HCl, pH 7.5 in the solution of 154 mmol L 1 NaCl, acetylthiocholine iodide was a substrate. Measurement of enzymatic activity was performed in fluorimeter polystyrene cuvettes for 3 min (UV/VIS spectrophotometer Shimadzu, Japan). The effects of 1 mmol L-1 NaF in the presence of 20 pmol L 1 A1C13 were measured. Data are expressed in percentage of the AChE activity in the absence of aluminum and fluoride ions. No differences between the AChE activity were found between the investigated groups...

Following successful recovery of peptide/protein molecule from the microspheres, a simple spectrophotometric method does not always allow discrimination between the monomeric protein form and its aggregates. However, HPLC might separate these species and thus provides more accurate qualitative data [96], But HPLC cannot quantify exclusively the amount of active protein antigen, as is the case with ELISA techniques [97], Nowadays, Fourier transform infrared (FTIR) spectroscopy has become a popular, noninvasive method, as it is able to characterize the secondary structure of entrapped proteins [26, 95, 98-101], Only recently, the integrity of their primary structure was evaluated, thanks to a new matrix-assisted laser... 

The first step in the evaluation process is to define and document the current system use and user requirement specifications. If the system will be changed in the foreseeable future, any resulting changes in the intended use of the system should be described as well. The definition should include a list of system functions, operational parameters and performance limits. For chromatography software required functions may include instrument control, data acquisition, peak integration through quantitation, file storage and retrieval and print-out of methods and data. If the system also includes spectrophotometric detectors, the functions for spectral evaluation should be specified as well. Table 2 lists items that should be included in the system documentation. 

The difference spectrophotometric technique (38) has been applied to P. notatum cellulase at pH 1.9 and 2.4 relative to native cellulase. Only a minor acid difference spectrum was obtained, while after heat denatura-tion a much more pronounced spectrum was observed. It was possible to evaluate from these measurements that a striking structural change has occurred in the environment of the tryptophyl groups upon heat denaturation. It may be concluded from these data that tryptophyl groups are buried in the interior of the native protein. 

ZEK/NAG] Zekany, L., NagypM, I., PSEQUAD a comprehensive program for the evaluation of potentiometric and/or spectrophotometric equilibrium data using analytical derivatives. Computational methods for the determination of formation constants, Leggett, D. J., Ed., Plenum Press, New York, (1991). Cited on page 317. 

This assertion is supported by the data in Table 1 concerning the behaviour of ARMCO iron in 1 m HCl solutions at various temperatures [40]. The direct evaluation of the corrosion current density. Id, was obtained from the determination of the concentration of ferrous ions, entered the solution, by the spectrophotometric technique. The galvanostatic pulse polarization curves were performed using the CORRCONTROL system [41] and the GALIMP program [42]. The corrosion current density, Ic, was computed using the NOLI method [34]. 

The spectrophotometric measurements in Table 2.1 are to be tested versus a normal distribution by means of Kolmogorov-Smirnov s test at a significance level of a = 0.05. In the first step, the empirical distribution function, F x), is evaluated as shown in Figure 2.10. For comparison of the hypothetical distribution function, the cumulative frequency by using the mean and the standard deviation of the data in dependence on the (standard normal) deviate z are plotted (cf. Eq. (2.28)). 

The latter ones have been determined by spectrophotometric measurements at four different wave numbers. The data in the table show the accuracy of measurement and evaluation.)... 

The FI methods developed for automation of ABTS +-based assay are listed in Table 31.2. All the methods have been successfully employed for the rapid evaluation of the anti-oxidative abilities of pure compounds, beverages, and food extracts. The TEAC values were calculated according to formula (31.9) or (31.10) in case of pure compounds and unknown samples, respectively. As can be seen from the data presented in Table 31.3, the Tr equivalents obtained by the FI methods are in quite good agreement with each other and with the TEAC values determined by the classic spectrophotometric ABTS assay. 

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