Standard operating procedure calibration models

Before using the pH electrode, it should be calibrated using two (or more) buffers of known pH. Many standard buffers are commercially available, with an accuracy of 0.01 pH unit. Calibration must be performed at the same temperature at which the measurement will be made care must be taken to match the temperature of samples and standards. The exact procedure depends on the model of pH meter used. Modern pH meters, such as the one shown in Figure 5.8, are microcomputer-controlled, and allow double-point calibration, slope calculation, temperature adjustment, and accuracy to +0.001 pH unit, all with few basic steps. The electrode must be stored in an aqueous solution when not in use, so that the hydrated gel layer of the glass does not dry out. A highly stable response can thus be obtained over long time periods. As with other ion-selective electrodes, the operator should consult the manufacturer s instructions for proper use. Commercial glass electrodes are remarkably... 

Procedure Using a suitably calibrated atomic absorption spectrophotometer and following the manufacturer s instructions for optimum operation of the spectrophotometer, determine the absorbance of the Standard Solution and of the Sample Solution at 589.0 nm. The absorbance of the Sample Solution is not greater than that of the Standard Solution. Viscosity of a 50% Solution Dissolve 200 g of sample, calculated on the dried basis and accurately weighed, in 200 mL of water contained in a 500-mL beaker. Equilibrate the solution at 25°, and measure its viscosity with a Brookfield viscometer A (model LVG, or equivalent), using a number 2 spindle at 20 rpm. 

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