EVALUATING ANALYTICAL PROCEDURES FOR QUANTIFYING AMMONIUM IN LEAF TISSUE

The effects of different methods of sample preparation, extraction, an d storage on the recovery of the combined pool of ammonia plus ammoniu m (NH3 + NH4+) from 'Washington' navel orange leaves previously incuba ted in solutions of increasing NH4Cl concentrations were assessed, Pro cedures and instruments for quantifying NH3 + NH4+ were tested for the ir sensitivity, reproducibility, and freedom from interference by amin o acids, Reliable recoveries of NH3 + NH4+, free from amino acid inter ference, were obtained with oven-dried (60C) leaves ground to pass thr ough a 40-mesh screen, extracted by homogenization in 10% TCA or by sh aking in 2% acetic acid, and then filtered and analyzed on the basis o f differences in electrical conductance between the sample and the ref erence cell, Methods measuring NH3 + NH4+ in KCl extracts by reaction with salicylate-nitroprusside in the presence of hypochlorite were com promised by significant color formation due to amino acids, Using fres h or freeze-dried leaf samples resulted in lower recoveries than use o f oven-dried samples. Storage at -20C of fresh or oven-dried leaf samp les in 10% TCA before or after homogenization and filtration did not a lter NH3 + NH4+ levels, whereas storage of these samples at 4C increas ed NH3 + NH4+ levels.