D974_9 (14e2)

Into an appropriate size irland Erlenmeyer flask or a beaker, introduce a weighed quantity of the sample as given in table one of the written standard. Add 100 milliliters of the titration solvent and 0.5 milliliters of the indicator solution, and without stoppering, swirl it until the sample is entirely dissolved by the solvent. If the mixture assumes a yellow-orange color, proceed as directed in 9.2 of the written standard. If it becomes green or green-black and base number analysis is required, proceed as directed in Section 10 of the written standard. In routine analysis, the indicator may be pre-mixed with a titration solvent before adding to the sample. Without delay, titrate at a temperature below 30 degrees Celsius. Note 14 of the written standard. Add 0.1 molar potassium hydroxide solution in increments, and mix to disperse the potassium hydroxide as necessary. See Note 12 of the written standard. Shake vigorously near the end point, but avoid dissolving carbon dioxide, CO2, in the solvent. In the case of acidic oils, the orange color changes to a green or green-brown as the end point is approached. When the solution first turns green or green-brown, reduce the increment size to m manual buret, or between 0.01 milliliters and 0.05 milliliters, automated buret. Continue until a persistent green or green-brown endpoint is reached-- see Note 13 of the written standard-- and held for a minimum of 15 seconds after the addition of the last increment, or if it reverses with two drops of 0.1 molar hydrochloric acid. When acid numbers about or below 1 are expected, better precision can be obtained by substituting 0.01 molar, or 0.05 molar solutions in 9.2 and 9.3 of the written standard. This substitution was not included in the development of a precision statement. To observe the endpoint of dark-colored oil, shake the flask vigorously to produce momentarily a slight foam when the color change occurs as the last few drops of titrant are added, and observe the titration under a white fluorescent lamp at benchtop level. The temperature can be measured by any suitable temperature measuring device. An automated photometric device may also be used to detect the titration endpoint. However, the precision estimates given in Section 15 of the written standard may not apply to this mode of titration. Perform a blank titration on 100 milliliters of the titration solvent, and 0.5 millimeters of the indicator solution, adding 0.1 milliliter or less increments of the 0.1 molar potassium hydroxide solution. The titration solvent usually contains weak acid impurities, which react with the strongly basic components of the sample. To correct the base number for the sample, determine an acid number blank upon the solvent.