Go-extracted ions with ATP from soils may interfere with ATP luciferin-luci
ferase luminescence reaction when ATP is assayed. The effects were investig
ated in a typical concentration range of cations and anions potentially ext
ractable in soils. A commercial ATP assay product (Sigma Chemical Co.) was
used. Significant quenching is evidenced from a concentration of 0.10 mM wi
th 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+. Becaus
e cation quenching can be alleviated by addition of EDTA, three forms of ED
TA (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 conce
ntrations 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 concentratio
ns significantly decreased light emission. The quenching by CO32- and Cl- w
as only observed at high concentrations (3.20 mM and up). The order of quen
ching 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 re
quire the ATP assay standards be prepared in a solution of similar chemical
composition to that in soil ATP extracts. (C) 2001 Elsevier Science Ltd. A
ll rights reserved.