Colorants standardization

Procedures for determining the quaUty of formaldehyde solutions ate outlined by ASTM (120). Analytical methods relevant to Table 5 foUow formaldehyde by the sodium sulfite method (D2194) methanol by specific gravity (D2380) acidity as formic acid by titration with sodium hydroxide (D2379) iron by colorimetry (D2087) and color (APHA) by comparison to platinum—cobalt color standards (D1209). 

Table 4. Commercial Pigment Colors, Standard Strength Pigments ...

Color Color Association of the United States 24 East 39th Street New York, NY 10016 Color standards for fabrics, paints, wallpaper, plastics, floor coverings, automotive and aeronautical materials, china, chemicals, dyestuffs, cosmetics, etc. 

Terephthahc acid is pure white, and molten dimethyl terephthalate is colorless. Impurities or degradation products can be yellow or brown, so the darkness of either a solution of terephthahc acid in dimethylform amide or molten dimethyl terephthalate can be compared to APHA color standards. 

Experienced color matchers can achieve a good color match by trial and error without using any instmmentation. In some cases, however, this technique can be a lengthy process, and should the desired match be outside the color space defined by the available color standards, the technician might spend too much time just to determine that the match is not possible. To get the most cost-effective match using a low metamerism in the shortest possible time, the use of a computet color matching system is preferable. 

Liquid cycloahphatic amines and diamines have exacting purity and color standards. Almost all are sold to specification, not performance standards. Use as isocyanate precursors requites low water content criteria for these hygroscopic fluids, hence nitrogen blanketing is often specified for product sampling as well as storage and transport. 

The acid wash test consists of shaking a mixture of 96% sulfuric acid with benzene and comparing the color of the (lower) acid layer with a set of color standards. Other quaUtative tests include those for SO2 and H2S determination. The copper strip corrosion test indicates the presence of acidic or corrosive sulfur impurities. The test for thiophene is colorimetric. 

Benzene reacts with concentrated sulfuric acid and formaldehyde to produce a brown precipitate. A similar reaction occurs with ferrous sulfate and hydrogen peroxide. The resulting brown soHd is dissolved in nitric acid for comparison with color standards. 

Gardner Color. Color measurement is obtained by comparing the sample with 18 separately numbered Gardner color standards. These are convenientiy mounted as glass disks on wheels. The entire apparatus, consisting of two wheels containing nine disks each, a case to enclose the wheels, and a slot ia the case for the sample, is commercially known as the HeUige Comparator (3). 

It is desirable for the record to have an objective statement of the nature and degree of color deterioration. The simplest, but least desirable, method is comparison of sample color with color charts or plates such as those used in the Munsell system, Ridgeway s color standards, or the Maerz and Paul dictionary of color. Such a method is limited in value because of the difficulty of obtaining true color matches, and because of variations due to human error. The use of color charts or plates may be much improved in the Munsell system by employing a disk colorimeter (29). Kramer and Smith (21) have pointed out that the results obtained in its application to foods are sometimes difficult to explain and compare, and that the method requires special training of the operator and is tedious and cumbersome. 

Not darker than color standard No 5 of ASTM platinum-cobalt scale Not more than 1° and shall... 

Thompson, T.E., Grauke, L.J., and Young, E., Pecan kernel color standards using the Munsell color notation system, J. Am. Soc. Hort. ScL, 121, 548, 1996. 

Color. Standards Stock standard. Dissolve 1.245g of potassium chloroplatinate (K2PtCl6) and l.OOOg of cobaltous chloride (C0CI26H2O) in water. Add 100ml of coned HQ, and dilute the soln to 1000.0ml with water. (This soln has a color of 500 on the APHA and ASTM platinum-cobalt scales)... 

The white plate is used by most investigators for standardization, but there may be instances where the colored standard is preferred. Whichever is chosen, that same plate must be used throughout the discoloration study. Additionally, the exact specifications of the standardization plate should be indicated in any scientific report. 

The choice of test equipment and methods has become extremely wide and, apart from large, integrated, electronic colorimetric and spectrophotometric instrumentation, field personnel can choose from miniburettes, direct-reading titrators (modified syringes), digital titrators, drop tests, tablet tests, permanent color standard comparators, indicator papers, portable colorimeters, immunoassays, etc. Today, field-test methods tend to be tailored by equipment manufacturers to their own analytical systems, and consequently the specified use of particular standard methods for the examination of water, from any one technology or official body, is probably not realistic. Rather it is the fitness-for-purpose rule that is more relevant. 

Lovibond tintometer—device for measuring the color of a petroleum product, particularly petrolatums. The melted petrolatum is contained in a cell and the color is compared with a series of yellow and red Lovibond glasses. The length of the cell and the color standards that give the best match are reported. See color scale. 

In Florida, color standards for fresh fruit are based entirely on the color of the peel (57). Subjective means are used to describe the color. For example, some of the USDA color grade standards for Florida oranges and tangelos are ... 

A. The color of orange juice is evaluated by comparing the color of the single strength or the properly reconstituted product with the USDA orange juice color standards, so that these color standards become points of reference. 

C. Classify the juice by inserting the sample tube where it fits best in the series of color standards. See Table IV. 

Availability of Color Standards. The USDA orange juice color standards cited in this section are official color standards. Information regarding the color standards and their availability may be obtained from ... 

As pink or red—fleshed grapefruit ripen, the color of the juice loses the distinct coloration and gives a juice that is definitely amber with a very slight brownish cast. Mixtures of white-fleshed and pink-fleshed grapefruit have a dull appearance and may look grayish to dull amber. There are no visual color standards for grapefruit juice products. However, color characteristics may be measured on tristimulus colorimeters using the L, a, b, color notation. 

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