Turbidity standard

Hach, C. C. Bryant, M. Turbidity Standards Technical Information... 

Combining SEC with MAES to produce absolute molar mass data without molecular calibration standards also requires prior calibration of the concentration detector as well as calibration of the MAES detector itself. The latter calibration involves the determination of all geometrical contributions such that the MAES detector measures the Rayleigh excess ratio at each scattering angle. This is most easily achieved by using a turbidity standard such as toluene. Details are found in Ref. 2. Once the refractive index of the mobile phase is entered, the software [4] performs the required calibration. 

For water analysis, the formulation of turbid standards is very difficult, so most water laboratories use a synthetic pol5mer suspension as a standard. The formazin polymer suspension is easy to make and more stable and reproducible than adding clay or other particles to water to prepare standards. Alternatively, suspensions of polymer beads of the appropriate size can be used as scattering standards. (See Standard Methods for the Examination of Water and Wastewater for details.)... 

American Public Health Association (1998) Turbidity. Standard Methods for the Examination of Water and Wastewater. American Public Health Association, American Water Works Association, and Water Pollution Control Federation. 

Synthetic turbidity standards are generally used in the quantitative measurement of turbidity. Alternatively, calibration curves can be obtained by precipitating known amounts of the substance to be measured. However, grain size depends not only on precipitation conditions, but also on the time delay between precipitation and measurement. so conditions must be standardized carefully to ensure reproducible results. Nephelometric and turbidimetric methods have also become important in recent years in continuous automatic on-line process control (e.g.. of wastewater). 

Name the chemical added to the turbidity standards to prevent the growth of bacteria or algae. 

Fowlef measured the turbidity of air at Mt. Wilson, California, on a clear day in 1913. Values of rx for dry air at different wavelengths are tabulated below, where x is essentially the thickness of the atmosphere corrected to standard temperature and pressure (STP) conditions ... 

Although color and turbidity of acid products are important properties, there is Httie standardization in such measurements. A ftequentiy used procedure is to determine color and turbidity by comparison with standards originally developed by the American PubHc Health Association (APHA) for examination of water (151). 

Sodium thiosulfate is determined by titration with standard iodine solution (37). Sulfate and sulfite are determined together by comparison of the turbidity produced when barium chloride is added after the iodine oxidation with the turbidity produced by a known quantity of sulfate iu the same volume of solution. The absence of sulfide is iadicated when the addition of alkaline lead acetate produces no color within one minute. 

Color. Many water samples have a yellow to brownish-yeUow color which is caused by natural substances, eg, leaves, bark, humus, and peat material. Turbidity in a sample can make the measurement of color uncertain and is usually removed by centrifiigation prior to analysis. The color is usually measured by comparison of the sample with known concentrations of colored solutions. A platinum—cobalt solution is used as the standard, and the unit of color is that produced by 1 mg/L platinum as chloroplatinate ion. The standard is prepared from potassium chloroplatinate (K PtCl ) and cobalt chloride (C0CI26H2O). The sample may also be compared to suitably caUbrated special glass color disks. 

The standard feedwell for a thickener is designed for a maximum vertical outlet velocity of about 1.5 iTi/min (5 ft/min). High turbidity... 

Method A. Weigh out accurately about 3.5 g of potassium cyanide from a glass-stoppered weighing bottle, dissolve it in water and make up to 250 mL in a graduated flask. Shake well. Transfer 25.0 mL of this solution by means of a burette and NOT a pipette to a 250 mL conical flask, add 75 mL water, 5-6 mL 6M ammonia solution, and 2 mL 10 per cent potassium iodide solution. Place the flask on a sheet of black paper, and titrate with standard 0.1 M silver nitrate. Add the silver nitrate solution dropwise as soon as the yellow colour of silver iodide shows any signs of persisting. When one drop produces a permanent turbidity, the end-point has been reached. 

Procedure (iodometric method). Weigh out accurately about 5.0 g of the bleaching powder into a clean glass mortar. Add a little water, and rub the mixture to a smooth paste. Add a little more water, triturate with the pestle, allow the mixture to settle, and pour off the milky liquid into a 500 mL graduated flask. Grind the residue with a little more water, and repeat the operation until the whole of the sample has been transferred to the flask either in solution or in a state of very fine suspension, and the mortar washed quite clean. The flask is then filled to the mark with distilled water, well shaken, and 50.0 mL of the turbid liquid immediately withdrawn with a pipette. This is transferred to a 250 mL conical flask, 25 mL of water added, followed by 2 g of iodate-free potassium iodide (or 20 mL of a 10 per cent solution) and 10 mL of glacial acetic acid. Titrate the liberated iodine with standard 0.1M sodium thiosulphate. 

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