AOAC RI ERP EBOOK FOR FERTILIZERS

Figure 2 Schematically comparisons of HPLC Results by two Labs

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Comparison of Urea analysis by Labs 1 & 2

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14

Lab 1 Lab 2

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10

% Urea-N

8

6

4

0

2

4

6

8

10

12

Sample #

When the same samples were analyzed by urease method based on the AOAC Official Method 959.03,the results are much different and in this case showed a high biased in ten of the analyses and low biased in the remaining two analyses. The results and the differences between the results from the urease method and the HPLC method are shown in Table 3.The lowest % Urea-N difference from the two methods shown in Table 3is -0.45 and the highest % Urea-N difference is 2.42. These results were obtained by a commercial lab using powdered form of urease made from Jack Bean meal.