EXTRACTING SOLUTION FOR POTENTIOMETRIC DETERMINATION OF NITRATE IN PLANT TISSUE

Rapid NO3- determinations were made potentiometrically on plant extracts using the Orion NO3- selective electrode. A 0.025M Al2(SO4)3 solution containing 10 μg. per ml. of NO3--N was used for extraction. The Al2(SO4)3 buffers against changes in the pH of the extract and the activity coefficient of NO3-. The pH is buffered close to 3.0 which depresses ionization of weak acids and, thus, interference from their anions. At the calculated 0.375M ionic strength of the extracting solution, the small increase in salt level from plant tissue extraction or KNO3 in the standards causes a negligible decrease in the activity coefficient of NO3-. Maintenance of a minimum of 10 μg. per ml. of NO3--N in extracts and standards resulted in more stable and rapid meter readings, linearity of the standard curve, and a reduction in the effect of interfering ions. © 1969, American Chemical Society. All rights reserved.