SCHEDULE 2METHODS OF ANALYSIS
8b.DETERMINATION OF DIFFERENT FORMS OF NITROGEN IN THE SAME SAMPLE — IN THE ABSENCE OF CYANAMIDE NITROGEN
Total soluble nitrogen
3.5
Urea nitrogen, either:
3.5.1
By conversion using urease, into ammonia, which is determined by titration with a standard solution of hydrochloric acid.
Or:
3.5.2
By gravimetry using xanthydrol: 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.
Or:
3.5.3
By difference, according to the following table:
Case | Nitric nitrogen | Ammoniacal nitrogen | Difference |
|---|---|---|---|
1 | Absent | Present | (3.1.1) – (3.4) |
2 | Present | Present | (3.2) – (3.4) |