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2. The titration may also be carried out using an indicator (4.26), although the change of colour is more difficult to observe.
See 7.2.3
where:
a = ml of standard solution of sodium or potassium hydroxide (0.1 N) (4.17) used for the blank, carried out in exactly the same conditions as the analysis.
A = ml of standard solution of sodium or potassium hydroxide (0.1 N) (4.17) used for the analysis.
M = weight of the sample, in grams, present in the aliquot part taken for analysis.
where:
a = ml of standard solution of sodium or potassium hydroxide (0.1 N) (4.17) used for the blank, carried out in exactly the same conditions as the analysis.
A = ml of standard solution of sodium or potassium hydroxide (0.1 N) (4.17) used for the analysis.
M = weight of the sample, in grams, present in the aliquot part taken for analysis.
Transfer by pipette into a 100 ml beaker a portion of the filtrate (7.1) containing not more than 20 mg urea. Add 40 ml acetic acid (4.11). Stir with a glass rod for one minute. Allow any precipitate to settle for five minutes. Filter, wash with a few ml acetic acid (4.11). Add 10 ml xanthydrol solution (4.23) to the filtrate drop by drop, stirring continuously with a glass rod. Allow to stand until the precipitate appears, then stir again for one or two minutes. Allow to stand for one and half hours. Filter through a sintered glass crucible (5.6) which has been previously dried and weighed, using a slight reduction in pressure. Wash three times with 5 ml ethanol (4.28), without trying to remove all the acetic acid. Place in an oven at a temperature of 130°C for one hour (do not exceed 145°C). Allow to cool in a desiccator and weigh.
where:
m = weight of the precipitate in grams.
M = weight of the sample, in grams, present in the aliquot part taken for analysis.
Correct for the blank.
Note: Although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers.
where:
m = weight of the precipitate in grams.
M = weight of the sample, in grams, present in the aliquot part taken for analysis.
Correct for the blank.
Note: Although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers.
Ureic N can also be calculated as indicated in the following table:
Case | Nitric N | Ammoniacal N | Ureic N |
---|---|---|---|
1 | Absent | Present | (7.2.4)-(7.5.3) |
2 | Present | Present | (7.3.3)-(7.5.3) |
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