PT  - JOURNAL ARTICLE
AU  - A. Richard Kenley
AU  - Michael Koberda
AU  - Wade DeMond
AU  - B. Richard Hammond
AU  - Jeff Hines
AU  - Kirk Ashline
AU  - Matthew Vincent
AU  - Rajaram Sriram
AU  - Alicia Martinez
AU  - Neervalur Raghavan
AU  - Corey Knight
TI  - Eliminating interferences in a Compendial Test for Oxidizable Substances in Water
DP  - 1990 Sep 01
TA  - PDA Journal of Pharmaceutical Science and Technology
PG  - 264--271
VI  - 44
IP  - 5
4099  - http://journal.pda.org/content/44/5/264.short
4100  - http://journal.pda.org/content/44/5/264.full
SO  - PDA J Pharm Sci Technol1990 Sep 01; 44
AB  - The United States Pharmacopeia (USP) uses acidified potassium permanganate to test for dissolved organics in pharmaceutical-grade water. In the test, a standard permanganate concentration is added to a boiling, acidified water sample. Visually inspecting the sample for residual permanganate determines whether the sample passes (pink color remains) or fails (pink color disappears) the test. The permanganate redox chemistry is complex, however, and test samples are prone to developing suspended particulate and colors other than pink. Forming hazy or off-colored solutions interferes with the subjective end point determination according to the USP test. We report two alternative end point determinations that essentially eliminate interferences from the compendial test method. The first alternative involves recording a uv-visible spectrum of the reduced permanganate test solution. Residual permanganate shows three distinct absorbance maxima at 510, 526, and 545 nm. It is straightforward to differentiate the characteristic permanganate fingerprint from the broad, lower-wavelength extinction that results from interfering substances. The second alternative involves filtering the reduced permanganate test solution through sintered glass. This filtration step removes manganese oxides and other colloidal particles that contribute to haze and off color formation in test samples.Visually inspecting the filtrate for residual pink color remains the end point determination for the test method. A third alternative method, namely spectrophotometric determination of permanganate loss rate constants is not a suitable alternative owing to a strong dependence of permanganate reduction rate on organic substrate structure.