Color determination method

Apparent equivalent weight deterrnined by titration with hydrochloric acid. APHA color determined by ASTM D1209, platinum—cobalt method. 

Hassan et al. [39] used a sensitive color reaction method for the determination of primaquine in pharmaceutical preparation. Primaquine was treated with diazo-p-nitroaniline in acidic medium to give an orange-yellow product with an absorbance maximum at 478 nm. When the medium was made alkaline, bathochromic, and hypochromic shifts occurred the new maximum was located at 525 nm. The mean percentage recoveries for authentic samples amounted to 100 and 100.21 by the acid and alkaline procedures, respectively (P = 0.05). Both reactions could be used to determine primaquine salts in pharmaceutical preparations. The results obtained were in good agreement with those of the official methods. Recoveries were quantitative by both methods. 

The perception of color is subjectively developed in the mind of an individual, and consequently different people can perceive a given color in various ways. Such variability in interpretation causes great difficulty in the evaluation of color-related phenomena, leading to problems in making objective judgements. The development of quantitative methods for color determination was undertaken to eliminate the subjectivity associated with visual interpretative measurements. 

This difference in kinetics was exploited to develop a procedure to determine free and reversibly bound sulfite in food. The mobile phase consisted of an aqueous solution of 0.05 M tetra-butylammonium hydroxide adjusted to the desired pH by the addition of glacial acetic acid (34). Fluorimetric detection is also possible, because a reaction of the formaldehyde-bisulfite complex with 5-aminofluorescein gives a nonfluorescent product. The sulfite is measured indirectly by its suppresion of the fluorescence of the reagent (31). This method is applicable to the determination of S02 at > 10 ppm and is not applicable to dark-colored foods or ingredients where SO, is strongly bound, e.g., caramel color. This method does not detect naturally occurring sulfite. Sulfur dioxide is released by direct alkali extraction. 

TheNafion-H given above exhibits acidic character comparable to 100% H2S04. The physical and chemical properties of the resins as reported by the manufactures are summarized in Table IV (55). It has been suggested that Nafion-H has an acidity between -11 and - 13 (8, 9), and we also determined it to be -12 by the visual color change method of the... 

Indian Pharmacopoeia determines the copper content using a color intensity method, according to the following procedure. Moisten 1 g of... 

As described in the previous section, azophenol crown 4 (n = 1) shows a characteristic coloration only for Li+ ion among alkali metal ions. After extensive examinations in a number of solvent systems, lithium analytical conditions were determined as shown in Table 2 [18a]. The resulting reddish purple color is very stable and its absorbance is maintained for 10-90 min after developing color. The calibration curve for Li+, in other words, sensitivity is linear from 25-250 ppb. Na+ does not interfere, but K+, Rb+, Ca2+, Sr2+, Ba2+, and Mg2+ interfered in the determination with a similar coloration. This method was applied to the analysis of a commercial pharmaceutical preparation, a lithium carbonate tablet, since the Li2C03 tablet has been used for medical treatment of manic depressive illness [18 b]. On the other hand, the azophenol crown 4 (n = 1) is also useful as a reagent for colorimetric determination of Rb+ and Cs+ [19]. 

Total Color Determine the total color strength as the weight percent of the sample taken using Methods I and II in Total Color under Colors, Appendix IIIC. Express the Total Color as the average of the two results. 

Color Determine by any suitable method, such as ASTM D 1500. 

Further studies into the possible effects historic cleaning methods had on garments could be valuable in explaining some fabric colorant behaviors presently exhibited by collected textile items of historical significance. It is recommended that the usefulness of x-ray analysis techniques to determine colorant type or residual effects of treatment be studied further. Tests similar to those conducted in this study could be done to test colorant responses to situations using a more refined color comparison method, such as the Hunter Color Difference Meter. 

Many varieties of red pepper, derived from plants of the genus Capsicum, are used in different cuisines around the world for their sensory properties of oral chemical "heat", volatile flavor and color. Determination of the degree of heat in a pepper sample has been a difficult problem for both sensory and instrumental analysts of flavor. Furthermore, the literature concerning the sensory physiology and perceptual responses of the "common chemical sense" (as defined later) has lagged behind other areas of study of the chemical senses. The purpose of this paper will be to review recent developments in two areas, the development of a standard method for sensory analysis of ground red pepper heat and the psychophysical characterization of observers responses to oral chemical Irritation induced by spice-derived compounds. 

The acid strengths shown in Table 17.3 were examined by the visual color change method using the Hammett indicators shown in Table 17.1 [43, 48]. The indicator dissolved in solvent was added to the sample in powder form in a nonpolar solvent, sulfuryl chloride [38] or cyclohexane [40]. The strength of colored materials such as S04/Fe203 and Mo03/Zr02 was estimated from their catalytic activities in comparison with those of the catalysts determined by the Hammett-indicator method. 

Color is a problem for scientific study. One aspect is the vocabulary one used to describe color. Mint green, bottle green, and Kelly green are nice names but not of great utility in that people s physical perception of color is not always the same. In some industries, such as colored fabric manufacture, current use is to send a set of standard colors which are matched by the producer. This is similar to the use of the Munsell color charts in geology. None of these processes makes use of physical optical spectral studies. The reason is that they are difficult to obtain and interpret. For a geologist, color is very important but we rarely have the possibility to standardize the method of our color perception. One reason is that color is both a reflective and transmission phenomenon. The thickness of the sample is critical to any transmission characteristics. Hence, a field color determination is different from one... 

Altliough methods involving organic solvent extraction or protein precipitation wfil estimate both free and protein-bound cortisol in tlie circulation, immunoassay-based methods that determine cortisol directly from serum have essentially replaced all extraction-based methods for routine cortisol measurements save for urine free cortisol methods. Flistorically four general methods have been used for the quantitative estimation of total blood cortisol concentrations in the clinical laboratory. These are the Porter-Silber color reaction method modified for plasma,the use of sulfuric acid-induced fluorescence, HPLC methods, or immunoassay. In general, HPLC and immunoassay are now used in both clinical laboratories and reference laboratories for the quantitative determination of cortisol in serum or urine. 

The mixing time can be determined by chemical means, if the tank contents is mixed with a reaction component and the component to be added is mixed with a (1 4- x)-fold equivalent of the second reaction component, so that after intimate mixing the two reaction partners react with one another. The disappearance of the reaction partner is shown by a color indicator, which experiences a sudden color change. ( Method of the last color change is used, in contrast with decolorizing reaction which is proportional to the degree of conversion, see e.g. Kappel [262]). The redox reactions of thiosulfate with iodine (indicator starch) and the neutralization of sodium hydroxide with sulfuric acid (indicator phenolphthalein) have been found to be simple fast ionic reactions, suitable for this purpose. 

The acid numbers obtained by this color indicator test method (ASTM D-974, IP 139) may or may not be numerically the same as those obtained by the potentiometric titration method (ASTM D-664, IP 177). In addition, the color of the crude oil sample can interfere with observation of the end point when the color indicator method is used. Determination of the acid number is more appropriate for various petroleum products. 

The Lowry assay [16] uses the reaction of cupric sulfate at alkaline pH in the presence of tartrate, producing a blue chromogen formed from four peptide bonds and one atom of copper. Addition of folin phenol reagent further enhances the color, with a maximum absorbance at 750 nm. The Lowry assay demonstrates the greatest sensitivity of the common protein concentration determination methods and varies only slightly when using the two common calibrators, BS A and BGG. Not surprisingly, this remains a very commonly used method. 

In the study of essential oils, the separation and isolation of the individual chemical constituents is critical in understanding the origin of the biological activity of these oils. This process also can eliminate undesirable compounds such as colorants and other materials, which may impart toxicity or have a detrimental effect on the biological activity or quality of the essential oil products. In follow-up studies, complete structural determination, in particular the relative and absolute stereochemical assignments, is critical for a complete understanding of the active compounds and their structure-activity-relationships. In this section, a brief general review of separation, isolation, and structure determination methods will be discussed. 

Birefringence Measurement. The polymer film was uniaxially heat-drawn at 90O at a rate of ca. 6.6 mm/min. in hot silicone oil. Birefringence of the drawn film was determined by a measuring the optical path difference between the parallel and perpendicular directions to the draw, using a crossed sensitive color plate method (Toshiba Glass Co., SVP-30-II). 

Moser, P. and Anliker, R. (1991) BCF and P limitations of the determination methods and interpretation of data in the case of organic colorants, in Bioaccumulation in Aquatic Systems (eds R. Nagel and R. Loskill), VCH, Weinheim. 

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