Browning color measurement

Changes in concentration as a function of time can be determined by measuring the increase in pressure as 2 gas molecules are converted to 5 gas molecules. Alternatively, concentration changes can be monitored by measuring the intensity of the brown color due to N02. Reactant and product concentrations as a function of time at 55°C are listed in Table 12.1. Note that the concentrations of N02 and 02 increase as the concentration of N2Os decreases. 

The solubility of [RhCl(C8H14)2]n in benzene and chloroform is too low for molecular-weight measurements. Its reddish-brown color darkens slowly in air. 

Table-TV shows the effect ot fhe LMW fraction on the activity of some of these enzymes in vitro. Maltase, lactase and invertase were competitively inhibited at a concentration of 10 mg/ ml. When the effectsof a range of concentrations (2.5-20 mg/ml) of the LMW fraction were studied, it was revealed that the inhibition was not of the pure competitive type. Table V shows the effect of the HMW fraction. Low concentrations had to be used in the assays, as the intense brown color of this fraction interfered with the spectrophotometric measurements. In spite of this a strong competitive inhibition of lactase and of invertase was found. Maltase was also inhibited, and, to a lesser extent, even trehalase. a-Amylase from saliva was not affected at the concentration tested.

The degree of Maillard reaction was estimated as amount of brown color produced. Samples were extracted in buffer of pH 8.0, proteins were precipitated by TCA and absorbance was measured at 375 nm spectrophotometrically according to a method by Laser Reutersward and Johansson (unpublished). 

Table II. Effect of creatinine concentrations on the mutagenic activity in crusts (dry matter) of fried beef. Creatine concentrations within parenthesis. Brown color as a measure of Maillard reaction products is given as absorbance at 375 nm per g dry matter...

Organophosphate. For the estimation of phosphoric acid esters, the developed plate is sprayed with 0.25% solution of palladium chloride in 0.1 N HC1 and dried in air. After exactly ten minutes, the area of the yellow-brown colored spot developed is measured and compared with that of the spots of standard insecticide solutions run alongside. 

The decomposition point as measured in the ordinary manner varies with the temperature of the bath at the time of the introduction of the sample. When the melting-point bath is heated so that the temperature rises by 2° per minute, a sample introduced just as the temperature reaches 200° develops an observable brown color at 206° and then darkens so rapidly that no liquid phase can be identified if, under the same conditions, the sample is introduced when the bath temperature is 238° the decomposition begins immediately but a liquid phase can be recognized when the bath temperature is in the range 241-243°. 

Ammonium Thiocyanate, 0.1 N (7.612 g NH4SCN per 1000 mL) Dissolve about 8 g of ammonium thiocyanate (NH4SCN) in 1000 mL of water, and standardize by titrating the solution against 0.1 N Silver Nitrate as follows Transfer about 30 mL of 0.1 N Silver Nitrate, accurately measured, into a glass-stoppered flask. Dilute with 50 mL of water, then add 2 mL of Ferric Ammonium Sulfate TS and 2 mL of nitric acid, and titrate with the ammonium thiocyanate solution to the first appearance of a red-brown color. Calculate the normality, and, if desired, adjust the solution to exactly 0.1 A. If desired, 0.1 N Ammonium Thiocyanate may be replaced by 0.1 A potassium thiocyanate where the former is directed in various tests and assays. 

Mercuric Nitrate, 0.1 M [32.46 g Hg(N03)2 per 1000 mL] Dissolve about 35 g of mercuric nitrate [Hg(N03)2-H20] in a mixture of 5 mL of nitric acid and 500 mL of water, and dilute with water to 1000 mL. Standardize the solution as follows Transfer an accurately measured volume of about 20 mL of the solution into an Erlenmeyer flask, and add 2 mL of nitric acid and 2 mL of Ferric Ammonium Sulfate TS. Cool to below 20°, and titrate with 0.1 N Ammonium Thiocyanate to the first appearance of a permanent brown color. Calculate the molarity. 

The color of the wax will affect the color of the finished product. A Lovibond Tintometer is often used for color measurements, whereby the color of the raw material is compared against a series of colored standard glasses, under a standard light source. The color of the solidified wax of the same sample may be different depending on the amount of occluded air, the rate of cooling, or surface finish. Therefore, the color of many waxes is best measured in the molten state. Two ASTM color standards are used to measure dark-brown to off-white color and off-white to pure white. The refractive index and the specific gravity are other parameters often determined. 

Basic and advanced life-support measures should be utilized. Activated charcoal without a cathartic may be used in early decontamination. Most ingestions are self-limiting. Treatment after decontamination is symptomatic and supportive. Monitoring of fluids and electrolytes is recommended for symptomatic patients. If a significant ingestion of anthraquinones does occur, Borntrager s reaction may occur (red color is seen in alkaline urine and a yellow-brown color in acid urine). No other specific laboratory tests are available to assist in diagnosis and treatment. 

An end point in a Karl Fischer titration can be observed visually based on the brown color of the excess reagent. More commonly, however, end points are obtained from electroanalytical measurements. Several instrument manufacturers offer automatic or semiautomatic instruments for performing Karl Fischer titrations. All of these are based on electrometric end point detection. The details of operation of Karl Fischer titrators are discussed in Chapter 22. 

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