The Titrimetric Assay of H⁺Excreted byRicinus communisCultivated on NH₄⁺-N Nutrient Media: The Effect of Ionic Strength and Nutrient Phosphate Concentration

Allen, C. R. and Allen, S. 1987. The titrimetric assay of H⁺ excreted by Ricinus communis cultivated on $NH4+$ -N nutrient media; the effect of ionic strength and nutrient phosphate concentration.— J. exp. Bot. 38: 597–606. The simple titrimetric assay of H⁺ excreted by $NH4+$ -N plants into spent nutrient solution was critically assessed on the basis of equations for charge balance, conservation of matter and chemical equilibrium (including activity coefficients). For Ricinus communis, a simple volumetric calculation from back-titration of the spent medium to 6–5 underestimated proton excretion by 3%, compared with the corresponding error of up to 50% for titrimetric assay of base excreted into spent $NO3-$ -N media.