Abstract
Flow injection procedures for the determination of water in methanol using Karl Fischer method are presented. Both
spectrophotometric and potentiometric detection systems were investigated and critically compared with respect to their
performance characteristics. A novel tubular differential potentiometric flow through cell has been developed. Using spec-trophotometric detection the determination of water at a sampling frequency of about 120 h−1 is possible in the concentration
range 0.01–1%. Precision is better than 3% R.S.D. over the entire concentration range. The detectability of the method is
severely affected by the presence of water traces in the carrier solvent but with appropriate preventive measures, concentrations
as low as 0.002% are accessible. The specifications of the potentiometric variant compare well with the spectrophotometric
detection method, yet the former offers slightly better precision but suffers from reduced linear range. Automation of the
two methods has been realised and the applicability for on-line monitoring purposes are outlined. Particular emphasis is paid
to the calibration problematic. Modified reverse FIA has also been applied and shown to be a simple and reliable way of
detecting deviations from nominal values as required in several process control situations. ©