Colorant testing sampling methods

The other two methods used by industry to examine the purity of maleic anhydride are the crystallization point (168) and color deterrnination of the sample (169). These tests determine the temperature at the point of solidification of the molten sample and the initial color properties of the melt. Furthermore, the color test also determines the color of the sample after a two-hour heat treatment at 140°C. The purpose of these tests is to determine the deviation in properties of the sample from those of pure maleic anhydride. This deviation is taken as an indication of the amount of contaminants in the maleic anhydride sample. 

Rapid, simple, quaUtative methods suitable for determining the presence of benzene in the workplace or surroundings have been utilized since the 1930s. Many early tests offered methods for detection of aromatics but were not specific for benzene. A straightforward test allowing selective detection of benzene involves nitration of a sample to y -dinitrobenzene and reaction of the resultant ether extract with an ethanoHc solution of sodium hydroxide and methyl ethyl ketone (2-butanone), followed by the addition of acetic acid to eliminate interferences from toluene and xylenes. Benzene imparts a persistent red color to the solution (87). The method is claimed to be sensitive to concentrations as low as 0.27 ppm benzene from 10 mL air samples. 

In this method, an ale soln of benzene-sulfonic acid(previously standardized with phosgene by weighing the pptd diphenyl-carbamide) is added from a burette to a sample of aniline(or its nitrated compd not jiighvr thsji tctrsnitro-) until the 3ppcufuptcc of a dirty-bluish coloration, when a drop of the reaction mist is placed on a filter paper previously impregnated with amino-/3-naphthol indicator(spot test). This method is not applicable for analysis of penta-nitroani ine(Ref 15)... 

The principle approach to immunoassay is illustrated in Figure 1, which shows a basic sandwich immunoassay. In this type of assay, an antibody to the analyte to be measured is immobilized onto a solid surface, such as a bead or a plastic (microtiter) plate. The test sample suspected of containing the analyte is mixed with the antibody beads or placed in the plastic plate, resulting in the formation of the antibody—analyte complex. A second antibody which carries an indicator reagent is then added to the mixture. This indicator may be a radioisotope, for RIA an enzyme, for EIA or a fluorophore, for fluorescence immunoassay (FIA). The antibody-indicator binds to the first antibody—analyte complex, free second antibody-indicator is washed away, and the two-antibody—analyte complex is quantified using a method compatible with the indicator reagent, such as quantifying radioactivity or enzyme-mediated color formation (see Automated instrumentation, clinical chemistry). 

Color Strength, Hue, Chroma [20, p. 99-105], The coloring properties of a dye are assessed by preparing a dyed test sample whose color is evaluated. This must, in principle, always be done by the human eye because color perception, being a subjective sense impression, is not accessible to direct measurement. However, with the aid of colorimetry this visual perception can be represented more or less closely by measurable quantities. Since colorimetry is an objective method and is therefore more accurate and reproducible than subjective visual assessment, it is veiy widely used today. Color is a three-dimensional quantity and must therefore be expressed by a set of three numbers (color coordinates). In practice, these are typically the values of color strength, hue, and chroma. 

Active Oxygen Method for Fat Stability (AOM) (Cd 12-57) determines the time (in hours) for a sample of fat or oil to attain a predetermined peroxide value (PV) under the conditions of the test. The method is used to estimate the comparative oxidative stability of fats and oils. The method has been placed in surplus, in favor of Cd 12b-92 (Oil Stability Index), but retains official status and is still used in domestic industry. p-Anisidine Value (AV) (Cd 18-90) determines the amount of aldehydes (principally 2-alkenals and 2,4-dienals) in animal and vegetable fats and oils. These are degradation products of peroxides, which are not removed by bleaching. Some fats and oils chemists propose increased use of this method in purchase specifications. Bleaching Test for Soybean Oil (Cc 8e-s63) determines the color of a sample of soybean oil after treatment with a specified bleaching earth. Specific methods exist for other oil species. 

Free formaldehyde is reacted with acetylacetone in the presence of an excess of an ammonium salt to form the yellow fluorescent compound, 3,5-diacetyl-1,4-dihydrolutidine and subsequently determined spectrophotometrically in methods A-E (14). In these methods, the test sample must be colorless and free from other carbonyl compounds. Some other derivatives have been used to analyze formaldehyde. For example, formaldehyde was reacted with sodium 4,5-dihydroxy-2,7-naphthalene disulfonate in sulfuric acid solution to yield a purple color (580 nm) and then subjected to colorimetric analysis. A purple-colored pararosaniline derivative was used to analyze formaldehyde in air (15). Air sample was passed through an aqueous solution which contained 0.4% of 3-methyl-2-benzothiazolone hydrazone hydrochloride and then a dye produced was determined at 635 or 670 nm (16). Molecular sieve (1.6 mm pettet) was used to trap formaldehyde in air samples. The formaldehyde... 

Color assessments include visual and spectrophotometric methods, both of which employ reference standards to aid in the communication of results. For instance, the visual method involves a comparison of the color of the test sample with known concentrations of potassium chloropalatinate (K PtCip and cobalt (II) chloride (CoCl ) in distilled water. The estimated color of the test sample is then used to calculate color units, using the following equation ... 

The American Public Health Association (APHA) also developed a method for evaluating the color of wastewater. Initially, this method was used as an indication of water purity and involved making comparisons of test samples with dilutions of a 500-ppm Pt-Co stock solution. In the APHA index system, distilled water is assigned a value of 0 (zero) and the stock Pt-Co solution has a value of 500. Details pertaining to the preparation of solutions and sample measurements are provided in ASTM D1209-93. In addition, ASTM D1209 describes how to correlate data from color measurement instruments with data from physical APHA and Pt-Co color standards. 

The test method for the determination of the acid number by the color indicator titration method (ASTM D-3339, IP 431) measures the acid number of oils obtained from a laboratory oxidation test (ASTM D-943) using smaller amounts of samples than those used in other acid number tests (ASTM D-664, ASTM D-974, IP 139, IP 177). 

The Saybolt color test method (ASTM D-156) is used for nearly colorless waxes, and in this method a melted sample is placed in a heated vertical tube mounted alongside a second tube containing standard color disks. An optical viewer allows simultaneous viewing of both tubes. The level of the sample is decreased until its color is lighter than that of the standard and the color number above this level is the Saybolt color. 

The optical microscope is a valuable tool in the laboratory and has numerous applications in most industries. Depending on the type of data that is required to solve a particular problem, optical microscopy can provide information on particle size, particle morphology, color, appearance, birefringence, etc. There are many accessories and techniques for optical microscopy that may be employed for the characterization of the physical properties of materials and the identification of unknowns, etc. Utilization of a hot-stage accessory on the microscope for the characterization of materials, including pharmaceutical solids (drug substances, excipients, formulations, etc.), can be extremely valuable. As with any instrument, there are many experimental conditions and techniques for the hot-stage microscope that may be used to collect different types of data. Often, various microscope objectives, optical filters, ramp rates, immersion media, sample preparation techniques, microchemical tests, fusion methods, etc., can be utilized. 

In the absence of any color, test io cc. of the sample in the same manner, using sufficient fusel oil, amyl alcohol or pentasol to nearly fill the tube, and shake several times. A deeply colored lower layer is an indication of a coal tar dye its identity should be confirmed by using the methods under 51. 

Small plastics extruders are often used to produce test samples for color matching, gel counts, physical testing, fire tests, etc. A capillary die can be added and used as a rheometer using the method described in ASTM D5422 [24]. 

The same sample was then analyzed for protein by the modified Folin-Ciocalteu method." A correction was made for the color of the antigen. To test the method ten triplicate analyses were run on purified antibody samples by both the modified Folin-Ciiocalteu and the Nessler method by two analysts. The first method gave values which averaged 1.035 0.035 times the second. 

British suspended particulate sampler In recent years the old British standard method has been super-ceded by European directives such as EN12341 Air Quality - Field test procedure to demonstrate reference equivalence of sampling methods for the PMIO fraction of particulate matter. The determination of smaller size fractions (PM2.5) is also covered by a further directive. The US EPA have similar standard reference methods for particulate material (USEPA 40 CFR part 50). An early method was to simply compare the color of a filter paper through which a volume of air was drawn to an incremental gray scale (16 shades from white to black) this was then converted into an integrated particle loading with reference to the size cut-off offered by the pore size of the filter used. This was known as the black smoke index method. 

Citotoxicity assays using murine neuroblastoma cells (Neuro-2A) have been proposed for the assessment of ciguatoxins and brevetoxins. The simplest method is based in the ability of metabolically active cells to reduce the tetrazolium compound MTT. After incubation with serial dilutions of test samples, cells are exposed to MTT and formation of color due to MTT reduction is read using a spectrophotometer. A new cytotoxicity assay is based on a c-fos-luciferase reporter gene that uses luciferase-catalyzed light generation as an endpoint and a microplate luminometer for quantification. After... 

In the blood, uric acid is distributed between red cells and serum. The proportion found in each fraction of the blood is determined by the Gibbs-Donnan equilibrium. Two types of methods are available for determining uric acid in blood—colorimetric and enzymic analyses. The colorimetric methods require preliminary precipitation of blood proteins, which entails coprecipitation of urates. In addition, the color tests are never rigidly specific for urates. For these reasons, accurate uric acid determinations are obtained only by treating the serum with uricase. The disappearance of uric acid from the sample can be determined by a spectrophotometric reading at 292 mp before and after enzymic treatment. 

---