Plasma in-liquid by means of anodic contact glow discharge electrolysis (aCGDE) is a grow- ing research ﬁeld allowing the selective modiﬁ- cation of the electrode and the electrolyte. The aim of this proof of concept study is to demon- strate that auxiliary electrochemical electrodes placed in vicinity to the plasma electrode, can be modiﬁed by aCGDE. Furthermore, we illus- trate in how far such auxiliary electrodes can be used as a probe to detect products (in particu- lar H2 , H2O2 , and O2 ) formed in the solution by aCGDE via electrochemical techniques. In this work aCGDE is achieved by applying a voltage of 580 V to a small Pt wire (plasma electrode) vs. a large stainless steel counter electrode. An auxiliary Pt electrochemical working electrode, operated in a three electrode conﬁguration, is placed at diﬀerent distances from the plasma working electrode. Depending on the distance, we ﬁnd small changes in the electrode struc- ture. More importantly, we will show that in principle the local H2 O2 concentration in the electrolyte can be monitored operando. After aCGDE the concentration changes with time and depends on the distance from the plasma electrode.