Usually, determination of DOPEG in plasma by EC-HPLC is always performed after extraction on alumina. This paper presents an extraction on boric acid gel, with good selectivity, reproducibility. In high sensitivity conditions (0.5 nA full scale) an autosampler is used and presents two major advantages: first, the possibility of storing samples in cold conditions to preserve stability of DOPEG, second the analysis of numerous samples in pharmacological studies, for example.