Evaluation of diffusion for inorganic-nitrogen analysis of natural water and wastewater

Public concern that agricultural use of N fertilizers may hare adverse effe cts on environmental quality and human health has led to a growing need for reliable data concerning the concentration of inorganic N in ground and su rface water. A study was conducted to compare the accuracy and precision of simple Mason-jar diffusion methods for quantitative determination of NH4and NO3- in a Hide variety of water and wastewater, relative to colorimetry , ion-selective potentiometry, and steam distillation. Good agreement among methods was generally obtained with standard solutions prepared using deio nized water; however, substantial differences often were observed with natu ral and anthropogenic samples, because of either Cl- interference in measur ements with the NO3- electrode or CO32- interference in distillation. Analy tical accuracy also was evaluated by measuring recovery of N added as (NH4) (2)SO4 or KNO3 (6 mg N L-1). With most oh the samples studied, quantitative recovery (97-103%) was not achieved by potentiometry or distillation. Quan titative recoveries usually were achieved by a manual Berthelot method for colorimetric determination of NH4+, whereas recovery was often incomplete w hen NO3- analyses were performed with an automated flow-injection system us ing Cd2+ reduction, Regardless of the sample matrix, diffusion was always a ccurate in measuring recovery of NH4+ or NO3-.