Rapid determination of piperazine-type stimulants in human urine by microextraction in packed sorbent after method optimization using a multivariate approach

This paper describes the analysis of piperazine-type stimulants [1-benzylpiperazine (BZP), 1-(3-trifluoromethylphenyl)piperazine (TFMPP), 1-(3-chlorophenyl)piperazine (mCPP) and 1-(4-methoxyphenyl)piperazine (MeOPP)] in low volume urine samples (0.1 mL) by microextraction in packed sorbent and liquid chromatography-diode array detection. Analyte extraction has been comprehensively optimized, and the influencing factors were screened by means of the fractional factorial design approach. Several parameters susceptible of influencing the process were studied, and these included extraction sorbent type (C8 and C18), sample dilution (1:2 and 1:4), number of aspirations through the device (2 and 8) and the amount of methanol on both the washing (0 and 10%) and eluting solvents (10 and 100%). The method was linear from 0.5 (lower limit of quantitation) to 5 μg mL−1, with determination coefficients higher than 0.99 for all compounds. Intra- and interday precision ranged from 1 to 9%, trueness was within a ±11% interval for all analytes, and analyte recoveries were of about 70% for mCPP and TFMPP, and of about 10% for MeOPP and BZP. The method has shown to be selective, as no interferences from endogenous substances were detected by analysis of blank samples, and the analytes were stable in the samples for short periods at room temperature, after three freeze/thaw cycles and in processed samples. Due to its simplicity and speed, this method can be successfully applied in the screening and quantitation of these compounds in urine samples, and is suitable for application in forensic toxicology routine analysis.