A double polymer membrane modified glass carbon electrode with poly (3-octylthiophene) (POT) was developed for trace analysis of Cr (VI) in the form of hydrogen chromate ions (HCrO4-) in an acidic solution (pH 2.0). POT was electrochemically polymerized on glassy carbon (GC) electrode surfaces by cyclic voltammetry (-0.1-2.5 V, 100 mV s(-1), four cycles). Subsequently, a 54 plasticized poly (vinyl chloride) (PVC) was drop cast onto the POT as a second polymer, forming a double-polymer membrane. This modified electrode's stripping voltammetric current demonstrated an enhanced response to the hydrogen chromate ion, achieving a lower limit of detection of 12 nM (nanomolar). Operated in the stripping voltammetric mode, this GC - POT/PVC - modified electrode had a linear current response between 30 nM and 1300 nM in drinking water. The electrode demonstrates good selectivity relative to ClO4- and NO3- ions; the lower limit of detection of hydrogen chromate was 20 and 16 nM for ClO4- and NO3- ions, respectively. All solutions were prepared in tap water, which contains Cl-, F-, and CO32- ions at mg levels. These measurements could provide information on the lipophilicity of different toxins, leading to a better understanding of their environmental toxicity and the risks they pose to humans. Published by Elsevier B.V.