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Abstract
A rapid stability-indicating method was developed to quantitatively determine methenamine mandelate in tablets. After dissolution of the sample in water methenamine is separated from its decomposition product formaldehyde by the use of solid-phase extraction. the determination of methenamine may then be carried out by several procedures. A spectrophotometric assay following hydrolysis of methenamine to formaldehyde appeared to be most suitable.
The simplicity and accuracy of the method compares favourable with the U.S.P. XXI method. the procedure can be advantageously used in stability and quality control studies of methenamine containing dosage forms.
Precision and accuracy were checked by comparing the results of 10 identical raw material samples and 10 tablet samples that were both assayed by this method and the USP XXI procedure (Tables 4 and 5).
The assay values for methenamine and the relative standard deviations were similar for both procedures in both raw material and tablets.
Above results show that the SPE procedures give accurate, precise and reliable values for the methenamine assay. Since no titrant standardizations or lengthly sample pretreatments have to be carried out the method is fast, which makes it very suitable for industrial quality control purposes. the method is also economical. No precious instruments are necessary; a simple colorimetric device is sufficient.
The extraction columns can be reused several times. Even after 10 regenerations the columns did not show any deterioration.
