Assessment of ionic quenching on soil ATP bioluminescence reaction

Go-extracted ions with ATP from soils may interfere with ATP luciferin-luciferase luminescence reaction when ATP is assayed. The effects were investigated in a typical concentration range of cations and anions potentially extractable in soils. A commercial ATP assay product (Sigma Chemical Co.) was used. Significant quenching is evidenced from a concentration of 0.10 mM with Cu2+ and Zn2+, and 1.00 mM with Ca2+. The order of quenching at 1.00 mM was: Cu2+ > Zn2+ Ca2+ = Na+ = Mg2+, while Mg2+ = Mn2+, both Ca2+ and Na+ > Mn2+. The quenching was found to be much more severe with selected special heavy metal cations with quenching in the order: Ti3+ > Hg2+ > Cr3+. Because cation quenching can be alleviated by addition of EDTA, three forms of EDTA (Mg, Na and acid EDTA) were tested for their suitability for the assay. The Mg-EDTA was found superior to the other two. Presence of PO43- at concentrations of 0.01 and 0.05 mM, and NO3- at 0.01 and 0.10 mM, significantly enhanced ATP light emission (8-13%). However, SO42- at similar concentrations significantly decreased light emission. The quenching by CO32- and Cl- was only observed at high concentrations (3.20 mM and up). The order of quenching for the anions at a concentration of 6.4 mM was: PO43- > CO32- > SO42- > NO3- > Cl-. Enhanced or depressed light emission induced by ions would produce significant over or underestimation of soil ATP. While addition of Mg EDTA may alleviate cation quenching, the interference from anions may require the ATP assay standards be prepared in a solution of similar chemical composition to that in soil ATP extracts. (C) 2001 Elsevier Science Ltd. All rights reserved.