http://www.legislation.gov.uk/nisr/1991/540/schedule/2/part/II/crossheading/determination-of-urean2/paragraph/3.7/madeThe Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1991Local GovernmentGovernment Printer for Northern Ireland2016-09-06AGRICULTURESCHEDULE 2METHODS OF ANALYSISPART II4.DETERMINATION OF UREAREAGENTS3.7Urea standard solution: 1 .O g per 100 ml (1 ml of this solution = 10 mg urea).