On-line coupling of solid-phase extraction, derivatization reaction and spectrophotometry by sequential injection analysis: Application to trifluoperazine assay in human urine

Introduction: This study deals with a new methodology of on-line solid-phase extraction (SPE), derivatization reaction and spectrophotometric measurement utilizing sequential injection analysis (SIA) technique. The method was applied for the assay of trifluoperazine in human urine. Methods: An SPE procedure was automated to perform sample clean-up, extraction and preconcentration into a homemade microcolumn connected to a SIA manifold. Unlike previous SIA methods, a simple SIA manifold included one syringe pump and one multi-position valve was constructed. This offered simplicity and rapidity to the proposed method (sampling frequency 11 sample h− 1). Spectrophotometric measurement was based on a fast oxidation of trifluoperazine by Ce(IV) in sulfuric acidic media resulting in a spectrophotometrically detectable chromophore measured at wavelength 500 nm. The SPE procedure was optimized by the univariate method while the derivatization reaction and spectrophotometric measurement were optimized by multivariate methods. Results: The method was linear in a range of 70-200 ng ml− 1 and accurate with a recovery of 92.7%. Relative standard deviation of repeatability (n = 10 in a day) and intermediate precision (n = 5 over a week) did not exceed 4.3% indicating satisfactory precision. The limits of detection and quantification were 18.2 and 55.2 ng ml− 1, respectively. The sensitivity of the method was improved by the preconcentration, the use of extended pathlength in the detection device and the optimization of absorbance measurement. The method is selective in the presence of chlordiazepoxide, which is sometimes taken in combination with trifluoperazine. Discussion: The method is suitable for the application of overdose and therapeutic drug monitoring in human urine.