Microdetermination of Methenamine in the Presence of Formaldehyde by Solid Phase Spectrophotometry

A sensitive spectrophotometric method for the determination of methenamine has been developed without any separation steps. Bromocresol green is adsorbed on Sephadex LH-20 gel but the sorption decreases in the presence of methenamine due to ion-pair formation between bromocresol green and methenamine in solution. This attenuation was used to the microdetermination of methenamine by measurement of absorbance of the solid phase (Sephadex LH-20 gel) in a 1.0 mm cell at 625 nm. Methenamine could be determined in the concentration range of 0.42–1.68  μ g mL −1 (10-mL Sample volume) with a relative standard deviation (RSD) of 0.03% ( n = 4 ). The detection limit obtained was 50  μ g L −1 for 10 mL sample volume. The method was used for determination of methenamine in industrial wastewater and a satisfactory result was obtained.