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？μg？mL？1 (10-mL Sample volume) with a relative standard deviation (RSD) of 0.03% ( ). The detection limit obtained was 50？μg？L？1 for 10？mL sample volume. The method was used for determination of methenamine in industrial wastewater and a satisfactory result was obtained. 1. Introduction Methenamine (MT), (CH2)6N4, also known as 1,3,5,7-tetraazatricyclo[3.3.1.13,7]decane, urotropine, hexamine, hexamethylenetetramine, formin, and aminoform (Figure 1), is a relatively old common urinary tract antiseptic [1]. It is also used for the production of plastic materials, explosives, phenolic resins, antibacterial pharmaceutics, disinfecting materials, in the rubber industry as an additive, and so forth [2]. The most common production method of MT in industrial scale is the reaction of formaldehyde with ammonia or ammonium salts [3, 4]. Methenamine wastewater that is formed in the production of MT usually contains residual amounts of MT and formaldehyde [5]. Figure 1: The molecular structure of methenamine. Many methods have been developed for the determination of milligram amounts of MT; these methods have been cited by Madsen et al. [6]. However, there are relatively few methods available for the determination of MT at microgram levels [6–8]. Determination of MT in the presence of formaldehyde and ammonia is difficult because most of methods are indirect determinations based on the determination of the amount of formaldehyde released after hydrolysis of MT in acidic condition [6]. Therefore, in order to determine the amount of formaldehyde formed from the hydrolysis of MT, the amount of formaldehyde originally present must be determined prior to hydrolysis and then subtracted from the amount of formaldehyde formed after hydrolysis. HPLC and GC methods have been described for the determination of MT with expensive apparatus that use organic solvents [7, 8]. The spectrophotometry has been also used for determination of MT with the use of organic compounds that react with MT [1, 9–13]. This study presents a sensitive Solid