Standard-addition determination of nitrogen in coal with an ammonia-sensitive electrode

After semimicro Kjeldahl digestion of the coal sample with a K(2)SO(4)-V(2)O(5)-Se catalyst and sulphuric acid, the digest is cooled, diluted with water, neutralized and then made alkaline with NaOH/EDTA solution. The ammonia thus formed is determined by measuring the potential of a properly conditioned ammonia-sensitive electrode containing an appropriate filling solution; a gravimetric standard-addition technique is used. Known additions of 1-2 mug of N per g to blank solutions enables all measurements of potential to be made in the linear region of the electrode-response curve. The electrode measurement procedure gives blank-corrected recoveries of between 99.0 and 101.0% for synthetic sample solutions. Results obtained for nitrogen in reference coal samples by the electrode procedure have been found to agree well with those obtained by other methods.