DETERMINATION OF NITROGEN IN FERTILIZER BY COMBUSTION - COLLABORATIVESTUDY

Fourteen laboratories participated in a collaborative study to compare abilities of AOAC modified copper catalyst Kjeldahl method, 978.02, a nd the generic combustion method, 990.03, to analyze the nitrogen cont ent of fertilizer materials. Combustion analyses are more time efficie nt, more accurate, and less hazardous than Kjeldahl analyses. There we re 3 different types of instrumentation involved in the collaborative study: (1) Leco FP-428 Nitrogen Determinator; (2) Perkin-Elmer 2410 Se ries II Nitrogen Analyzer; (3) Carlo-Erba 1500 Series II Nitrogen Anal yzer. Thirty samples of fertilizer containing 167% N included 2 ACS gr ade standard materials: ammonium nitrate, theory 35.00% N; and dicyand iamide, theory 66.64% N. A diammonium phosphate and urea mixture (3 1; 1.0 mm grind) and 2 ACS grade standard materials of ammonium nitrat e and ammonium sulfate were supplied for repetitive combustion analyse s. Overall method performance of the combustion method was at least as good as the modified Kjeldahl method. Repeatability standard deviatio n (S(r)) values for the combustion method ranged from 0.09 to 0.34 vs the modified Kjeldahl method range of 0.06-0.49; reproducibility stand ard deviation (S(R)) values for the combustion method ranged from 0.13 to 1.07 vs the range of 0.09-3.57 for the modified Kjeldahl method. T he grand mean was 20.78% for the combustion method, and 20.79% for the modified Kjeldahl method using various fertilizers. The average range s Of S(r) and S(R) for the methods were, respectively, 0.17 and 0.29 f or the combustion method, and 0.19 and 0.54 for the modified Kjeldahl method. The method was adopted first action by AOAC INTERNATIONAL.