Research chemistMember of ASTM, Materials Division, Office of Research, Federal Highway Administration, HRS-23, Washington, D.C.,
Errors occur in the analysis of cement and concrete samples containing less than 0.02% Cl when the potentiometric ion electrode titration method published earlier is used (Journal of Materials, JMLSA, Vol. 7, No. 3, 1972, pp. 330–335). Slow nucleation of AgCl and slow equilibration produce large initial voltage increments which may be mistaken for the end point. A preliminary addition of 1 or 2 ml of 0.01 N NaCl delays the end point and places it in a nonambiguous region of the titration. Examples are given of titrations with and without the NaCl addition and a technique for handling millivoltmeter needle instability is described.
Paper ID: JTE10163J