COMPARISON OF 4 METHODS FOR FORAGE NITRATE ANALYSIS

Twenty forage samples were collected and selected for variation in nit rate content. Each forage sample was analyzed 4 times by 4 different m ethods: diphenylamine spot plate, spectrophotometric, nitrate-selectiv e electrode, and high-performance liquid chromatographic. Five feed ex tracts were spiked with 2 different amounts of nitrate and analyzed by each method. The spectrophotometric and nitrate-selective electrode h ad similar percent recoveries, which were close to 100%. The nitrate-s elective electrode method had the least variation of the 4 methods. Th e diphenylamine spot plate method had the poorest average recovery, gr eatest variation, and was the least accurate. The average coefficients of variation for all samples within a method were 15%, 12%, 6.4%, and 16% for the diphenylamine spot plate, spectrophotometric, nitrate-sel ective electrode, and high-performance liquid chromatographic methods, respectively. The variation in the nitrate-selective electrode method was lower (P < 0.05) than the other methods. The results from this st udy suggest that the nitrate-selective electrode method is more accura te and precise than the other methods of analysis tested.