  A dedicated test of the effects of Oxygen contamination in liquid Argon has
been performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArP
R&D program. Two detectors have been used: the WArP 2.3 lt prototype and a
small (0.7 lt) dedicated detector, coupled with a system for the injection of
controlled amounts of gaseous Oxygen. Purpose of the test with the 0.7 lt
detector is to detect the reduction of the long-lived component lifetime of the
Argon scintillation light emission at increasing O2 concentration. Data from
the WArP prototype are used for determining the behavior of both the ionization
electron lifetime and the scintillation long-lived component lifetime during
the O2-purification process activated in closed loop during the acquisition
run. The electron lifetime measurements allow to infer the O2 content of the
Argon and correlate it with the long-lived scintillation lifetime data. The
effect of Oxygen contamination on the scintillation light has been thus
measured over a wide range of O2 concentration, spanning from about 10^-3 ppm
up to about 10 ppm. The rate constant of the light quenching process induced by
Oxygen in LAr has been found to be k'(O2)=0.54+-0.03 micros^-1 ppm^-1.
