Mikrochim. Acta [Wien] 1986 III, 175--186 O by Springer-Verlag 1987 Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-4260, U.S.A. Measurement of Total Alkali and Phenol in Process Liquor by FIA J. A. Sweileh, P. K. Dasgupta*, and J. L. Lopez Abstract. Flow injection analysis (FIA) has been applied to the determination of total phenol and total alkali in high concentra- tion alkaline phenoxide liquors as it occurs in industrial process streams. The total alkali content and total phenol content in sam- ples containing 20--50% (w/v) sodium phenoxide can be directly measured without mutual interference. The first is measured by peak width measurement based FIA with conductimetric detection utilizing an electronic circuit to permit automatic measurement from minima to minima. The total phenol is measured by the Berthelot reaction using NaOC1 and ammonia to form indophenol blue, monitored at 660 nm with a light emitting diode-based detector. Key words: phenol, total alkali, FIA, industrial phenol liquor. Phenol is used for a great variety of products: dyes, plastics, ex- plosives, medicines and perfume. Concentrated aqueous phenol li- quors (20--50% w/w) are involved in its manufacturing [1]. These solutions typically contain up to a 10% stoichiometric excess or deficit of sodium hydroxide. Other compounds generally occur only in traces. Reliable routine determinations of total alkali (sodium phenoxide and free sodium hydroxide, if any) and total phenol (phenoxide + free phenol, if any) are necessary in this caustic, cor- rosive, and odorous liquor. Direct photometric measurements in the UV to determine total phenol suffers from errors due to pH varia- tion; the absorbance at the phenol-phenoxide isosbestic point is too high for convenient measurement. Potentiometric acid base titra- * To whom correspondence should be addressed.