The AOx-based O2 scavenger system was further tested for its ability to maintain anaerobic conditions. The presence of O2 was qualitatively monitored by cyclic voltammetry using a glassy carbon electrode (GCE) as the working electrode in a small volume electrochemical cells open to ambient air. Before the addition of the O2 scavenging system, the O2 reduction appears at a potential lower than -0.1 V vs SHE on the GCE as a large irreversible cathodic current response (Figure and Figure ). After addition of the O2 scavenging system into the solution, the O2 reduction signal disappears which confirms the effective O2 removal (Figure and Figure ). With 5 mg L -1 paraformaldehyde, the anaerobic condition was maintained for at least 4.5 hours in solutions exposed to air, as demonstrated by the absence of any O2 reduction signal in the 20 successive CVs (Figure ). Similar results were obtained using EtOH as the reducing agent instead of paraformaldehyde (Figure ). CVs (2 mV s -1 ) of a GCE in electrolyte (1 mL) with AOx, CAT and Fc(MeOH)2 (100 µM, red trace) and upon addition of paraformaldehyde (5 mg mL -1 , blue trace). f) CVs (10 mV s -1 ) of a GCE modified with Os-complex modified polymer with AOx and CAT (red trace) and upon addition of paraformaldehyde (5 mg mL -1 , blue trace).