Zone fluidics for measurement of octanol–water partition coefficient of drugs Panwadee Wattanasin a, b , Phoonthawee Saetear a, b , Prapin Wilairat a, b, c , Duangjai Nacapricha a, b, **, Saowapak Teerasong a, d, * a FlowInnovation-Research for Science and Technology Laboratories (FIRST labs.), Thailand b Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand c National Doping Control Centre, Mahidol University, Bangkok 10400, Thailand d Department of Chemistry and Applied Analytical Chemistry Research Unit, Faculty of Science, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand H I G H L I G H T S G R A P H I C A L A B S T R A C T  An automatedzone-microfluidic sys- tem is presented for screening of octanol–water partition coefficient (P ow ).  Requires onlyone-phase measure- ment.  Vertically aligned holding column improves eliminates zone breakage. A R T I C L E I N F O Article history: Received 10 June 2014 Received in revised form 8 August 2014 Accepted 12 August 2014 Available online xxx This paper is dedicated to Prof. Kate Grudpan on the anniversary of his 60th birthday. Keywords: Zone fluidics Octanol–water partition coefficient Drug discovery A B S T R A C T A novel zone fluidics (ZF) system for the determination of the octanol–water partition coefficient (P ow ) of drugs was developed. The ZF system consisted of a syringe pump with a selection valve, a holding column, a silica capillaryflow-cell and anin-line spectrophotometer. Exact microliter volumes of solvents (octanol and phosphate buffer saline) and a solution of the drug, sandwiched between air segments, were sequentially loaded into the vertically aligned holding column. Distribution of the drug between the aqueous and octanol phases occurred by the oscillation movement of the syringe pump piston. Phase separation occurred due to the difference in densities. The liquid zones were then pushed into the detection flow cell. In this method, absorbance measurements in only one of the phase (octanol or aqueous) were employed, which together with the volumes of the solvents and pure drug sample, allowed the calculation of the P ow . The developed system was applied to the determination of the P ow of some common drugs. The log (P ow ) values agreed well with a batch method (R 2 = 0.999) and literature (R 2 = 0.997). Standard deviations for intra- and inter-day analyses were both less than 0.1log unit. This ZF system provides a robust and automated method for screening of P ow values in the drug discovery process. ã 2014 Elsevier B.V. All rights reserved. * Corresponding author at: Department of Chemistry and Applied Analytical Chemistry Research Unit, Faculty of Science, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand. Tel.: +66 2 329 8400; fax: +66 2 329 8428. ** Corresponding author at: Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand. E-mail addresses: duangjai.nac@mahidol.ac.th (D. Nacapricha), saowapak_teerasong@hotmail.com, ktsaowap@kmitl.ac.th (S. Teerasong). http://dx.doi.org/10.1016/j.aca.2014.08.025 0003-2670/ ã 2014 Elsevier B.V. All rights reserved. Analytica Chimica Acta xxx (2014) xxx–xxx G Model ACA 233425 No. of Pages 7 Please cite this article in press as: P. Wattanasin, et al., Zone fluidics for measurement of octanol–water partition coefficient of drugs, Anal. Chim. Acta (2014), http://dx.doi.org/10.1016/j.aca.2014.08.025 Contents lists available at ScienceDirect Analytica Chimica Acta journa l home page : www.e lsevier.com/loca te/aca