In accordance with the research specifications and guidelines in China, we developed a novel experimental method to detect new piperazine-type drugs, such as 1-(3-trifluoromethylphenyl) piperazine and 1-(3-chlorophenyl) piperazine. In this study, a new pretreatment method and gas chromatography (GC)/nitrogen-phosphorus detector detection technique were used to characterize these two kinds of drugs in urine and blood samples. For the purpose of isolation of these trace drugs from the samples, liquid-liquid extraction/solid-phase extraction was modified and validated for this specific study. The pretreatment method presented in this paper has many advantages, such as high recovery rate, high extraction efficiency, high detection sensitivity, low limit of detection, and simple operation. The GC/NPD instrument is popular in most laboratories because it can meet the routine requirements of forensic science. All these aspects make this combination of sample pretreatment and GC/NPD technique the most suitable choice for drug detection in biological samples.