Colorimetric measurements

Phosphatase Test. The phosphatase [9001-78-9] test is a chemical method for measuring the efficiency of pasteurization. AH raw milk contains phosphatase and the thermal resistance of this enzyme is greater than that of pathogens over the range of time and temperature of heat treatments recognized for proper pasteurization. Phosphatase tests are based on the principle that alkaline phosphatase is able, under proper conditions of temperature and pH, to Hberate phenol [108-95-2] from a disodium phenyl phosphate substrate. The amount of Hberated phenol, which is proportional to the amount of enzyme present, is determined by the reaction of Hberated phenol with 2,6-dichloroquinone chloroimide and colorimetric measurement of the indophenol blue formed. Under-pasteurization as well as contamination of a properly pasteurized product with raw milk can be detected by this test. 

As an example, take the molecule aminoazobenzene, one of the solutes listed in Table 39. When colorimetric measurements were made at room temperature on very dilute aqueous solutions of HC1, containing a trace of this substance, it was found that neutral molecules and (BH)+ ions were present in equal numbers when the concentration of the HCl was 0.0016 molal.1 At this low concentration the activity coefficient of the HCl is very near unity, and we may use (216) to find how far the vacant proton level provided by the aminoazobenzene molecule in aque-... 

The scales of spectrophotometers are often calibrated to read directly in absorbances, and frequently also in percentage transmittance. It may be mentioned that for colorimetric measurements I0 is usually understood as the intensity of the light transmitted by the pure solvent, or the intensity of the light entering the solution /, is the intensity of the light emerging from the solution, or transmitted by the solution. It will be noted that ... 

The basic principle of most colorimetric measurements consists in comparing under well-defined conditions the colour produced by the substance in unknown amount with the same colour produced by a known amount of the material being determined. The quantitative comparison of these two solutions may, in general, be carried out by one or more of six methods. It is not essential to prepare a series of standards with the spectrophotometer the molar absorption coefficient can be calculated from one measurement of the absorbance or... 

Principles and Characteristics Combustion analysis is used primarily to determine C, H, N, O, S, P, and halogens in a variety of organic and inorganic materials (gas, liquid or solid) at trace to per cent level, e.g. for the determination of organic-bound halogens in epoxy moulding resins, halogenated hydrocarbons, brominated resins, phosphorous in flame-retardant materials, etc. Sample quantities are dependent upon the concentration level of the analyte. A precise assay can usually be obtained with a few mg of material. Combustions are performed under controlled conditions, usually in the presence of catalysts. Oxidative combustions are most common. The element of interest is converted into a reaction product, which is then determined by techniques such as GC, IC, ion-selective electrode, titrime-try, or colorimetric measurement. Various combustion techniques are commonly used. 

Laing, D.K. Dudley, R.J. Issacs, M.D.J. Colorimetric Measurements of Small Paint Fragments Using Microspectrophotometry, Forensic Science International. 1980, 16, 159-171. 

Differential refraction( ) and colorimetric measurements ) were used to determine the amount of carbohydrate polymer adsorbed from solution. A Phillips X-ray diffractometer was used to quantify the degree of interlayer expansion(60. The cation exchange capacity of the peptized sodium and potassium... 

Temperature of measurement varies between 22.5-35°C. 6 O. P. = osmotic-pressure measurements t = light-scattering measurements C. = colorimetric measurements S. D. = sedimentation and diffusion measurements. 

Flow injection analysis has been used for the automated determination of hydrogen sulfide in seawater [20]. A low-sensitivity flow injection analysis manifold for concentrations up to 200 imol/l hydrogen sulfide had a detection limit of 0.12 xmol/l. Sulfide standards were calibrated by colorimetric measurement of the excess tri-iodide ion remaining after reaction of sulfide with iodine. The coefficient of variation was less than 1% at concentrations greater than 10 imol/l. The method was fast, accurate, sensitive enough for most natural waters, and could be used both for discrete and continuous analysis. 

In colorimetric terms, color differences are generally characterized by the distance between two colors in one of the color notation systems, most commonly the CIELAB system. The difference determined in this way represents the total color difference. Since a color is characterized by three quantities, a color difference can also be expressed in terms of three difference components (that is, differences in the color coordinates) and thus described in greater detail. Visually equal color differences between almost equal colors may, upon colorimetric measurement, be considered distinct if the colors of one pair differ strongly from those of the other pair. The formulas for color differences are further elaborated in order to remedy this defect. 

Also, boron can be analyzed by colorimetry techniques (APHA, AWWA, and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington DC American Public Health Association). Boron in acidified aqueous phase reacts with curcumin to form a red-colored product, roso-cyanine. Presence of calcium and magnesium at high concentrations can interfere in the test. Another colorimetric measurement involves the reaction of boron with carmine or carminic acid in concentrated sulfuric acid. The color of the solution changes from bright red to bluish red or blue, depending on boron concentration. 

Iron ammonium sulfate is an analytical reagent in titrations and colorimetric measurements to measure oxidizing substances, such as chlorine, or to measure the chemical oxygen demand in waste water. The compound is used to prepare Fe(II) standard solution for these analyses. It also is a cahbration... 

The orthophosphate anion, P04 can be analyzed readily in aqueous solution by either ion chromatography or colorimetry. The aqueous solution must be diluted for such analyses. In colorimetric measurement, the solution is treated with a reagent mixture containing ammonium molybdate and ammo-... 

Elemental composition Ag 69.19%, S 10.28%, O 20.52%. The salt is dissolved in nitric acid, the solution diluted, and analyzed for sdver. It is very slightly soluble in water. The supernatant solution containing trace sulfate anion may be measured by ion chromatography or by treating with barium chloride followed by colorimetric measurement at 420 nm. 

Tellurium and its compounds can be analysed by AA, ICP-AES and other spectrophotometric methods. Also, the metal can be identified by volumetric, gravimetric, and simple colorimetric measurements. 

Colorimetric measurements have been applied to various analyses of red wines and model wine solutions. °° ° ° Accurate definitions of the wines have been achieved by the L (lightness) and a (redness) values, while the representation of AL against AC revealed the color differences between various wines. ° The color stability of wine and model wine solutions toward storage time and bleaching by sulfur dioxide has been extensively studied by Bakker et while the color stability of a range of anthocyanin-containing... 

JJ)M,A. Laccetti, S. Semel M. Roth, AnalChem 31, 1049—50(1959). The fermus sulfate-sulfuric acid method is used to differentiate HMX and RDX from NGu, Tetryl, TEGN, PETN, NG K nitrate. Following the procedure given (which requires the colorimetric measurement of the color produced on dissolving the sample in the reagent) reveals that HMX and RDX have Beet s Law... 

Refs on Analysis of NG 1) Marshall 2(1917), pp 739—40 (Estimation of small quantities by reaction with phenol disulfonic acid to form. PA and colorimetric measurement against K nitrate standards) 2) Koehler et al, AnnChimAnal-ChimAppl 2, 271-2(1920) CA H 3794(1920) (Devarda method) 3) W.W. Becker, lECAnalEd 5, 152-4(1933) CA 27, 2909U933)(Redox method for NG and NGc in the presence of DNT)... 

St CA 45, 6l56(1951)(Reverse Redox method) 9) M. Halse, MeddNotskFarm-Selskap 16, 166-9(1954) CA 49, 13024(1955) (Determination of NG in mixtures with PETN) (Saponification to nitrite at 20°, then reaction with sulfanilic acid and a-naphthyl amine for a colorimetric measurment against nitrite standards) 10) P. Lhoste, MP 37, 149-52(1955)... 

Apparent In Situ Particulate Burden Based on Colorimetric Measurement... 

Matsuda, Y., Akazawa, R.,Teraoka, R., and Totsuka, M. (1994), Pharmaceutical evaluation of carbamazepine modifications Comparative study of photostability of carbamazepine polymorphs by using fourier-transformed reflection-absorption infrared spectrocopy and colorimetric measurement, / Pharm. Pharmacol., 46,162-167. 

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