This method is for the analysis of used refinery causticsolutions. Part A is for determining the strong base, weak base(spent caustic) and total alkalinity. Part B is for determining theconcentration of sulfur present as sodium sulfide and sodiummercaptide. The data generated using this method are consideredquantitative over the concentration ranges generally encountered inthese types of refinery caustic solutions. Refinery caustic samplesare inherently unstable, and must be analyzed as soon as possibleafter they are drawn.

Part A, a potentiometric titration, is an accurate procedure foruse in distinguishing between strong bases, i.e., sodium phenolateand sodium hydroxide. The APPENDIX contains a procedure, CausticSolution Analysis - Double Indicator, which can be used as aconvenient, although not rigorous, test for the plant control ofrefinery caustic solutions used to remove hydrogen sulfide,mercaptans and certain other weak acids from petroleumproducts.