Optimization of solid phase extraction conditions of diazepam from human plasma using statistical screening and response surface method

Plackett-Burman(P-B) design and Central Composite Design(CCD) were applied to optimize 6 factors for the extraction diazepam by solid phase extraction.The P-B design and its following statistical analysis indicate that the pH,sample speed,eluent dosage were the 3 key factors which significantly influenced recovery of diazepam as the response objective,and a quadratic model was obtained by CCD for the 3 factors by analysis of response surface optimization.Under the optimal extraction conditions,pH 10.20,sample speed of 0.67 mL/min and eluent dosage of 2.60 mL,the recovery of diazepam reached 91.26%.The calibration curves were linear over the concentration range of 0.10～10.00 μg/mL(R20.99) and the lower limit of quantification(LOQ) was 0.07 μg/mL.The intra-and inter-day precision(RSD) were less than 10% and accuracy(RE) was less than±6.0%.