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Table-4
Analyses of Urea using Different Sources of Urease
0.1 g
0.3 g
0.6 g
1.0 g
1
20 ml (1%Sol.)
100.1
100.1
99.7
99.9
2
10 ml Glycerol Ext.
99.9
99.7
99.7
69.9
2
20 ml Glycerol Ext.
99.9
99.7
99.7
99.4
3
20 ml (1%Sol.)
99.6
99.7
97.6
62.7
4
20 ml (1%Sol.)
99.3
99.7
83.2
52.6
5
2 tablets
100
98.6
69.3
45.5
6
20 ml Glycerol Ext.
99.9
99.9
99.7
99.5
7
20 ml (1%Sol.)
100.3
100.1
99.9
99.6
% Hydrolysis of urea from the amount used
Urease Amount
Urease
Source
In the amount used, all seven urease sourceshydrolyzed up to about 0.3 grams, thus exceeding the
AOAC method requirements. However the urease tablets (source No. 5) begins to fade in effectiveness
at 0.3 grams urea, with only 98.6% hydrolyzed, and two urease powders (No. 3and No. 4) begin to fail at
about 0.6 grams of urea. The two other powder samples (No. 1 and No. 7) and the two urease glycerol
extracts (No. 2 and No. 6) in 20 ml increments all hydrolyzed up to 1.0 gram of urea. Powder No.7 was
known from the manufacturer’s label to have a very high urease activity. From the results, it appears
that sources 1, 2, and 6 were high activity urease samples. These data show that the AOAC Official
Method 959.03 works well for pure urea when applied within the limits of the method. However, if the
amount of urea exceeds the recommended amount in the method, there are inconsistencies with the
results and some urease sources work better than others.
The inconsistencies with the Urease Method are obvious when the method applies to the more complex
fertilizer samples, namely, the Urea-Triazone liquid solution containing mixed compositions of urea-
forms and triazone moieties (Table 2).
More tests were done to further illustrate these inconsistencies even further.
In the following sets of experiments, five Urea-Triazone fertilizers from four different manufacturers
were analyzed for their claim of %SRN. The percentage of free and unreacted urea in these samples was
analyzed by the HPLC and by the urease methodusing powdered urease enzyme from Jack bean meal.
The results are shown in Table 5.