Determination of n-octanol–water partition coefficients by hollow-fiber membrane solvent microextraction coupled with HPLC

Simultaneous determination of the lipophilicity and dissociation constants of dialkyl phosphinic acids by negligible depletion hollow fiber membrane-protected liquid-phase microextraction

Determination of the physicochemical properties, especially the lipophilicity (expressed as the logarithm of distribution coefficient, log D) and dissociation constant (pK_a), is of great importance in the early stage of environmental risk assessment for an ionizable compound without these data. Currently, the log D and pK_a values of dialkyl phosphinic acids (DPAs), the environmental hydrolysates of aluminum dialkyl phosphinates (ADPs) that is one class of emerging phosphorus-containing flame retardants, are not available. In this study, the log D and pK_a values of three DPAs including methylethylphosphinic acid (MEPA), diethylphosphinic acid (DEPA) and methylcyclohexyl phosphinic acid (MHPA), were simultaneously determined by negligible depletion hollow fiber supported liquid phase microextraction (nd-HF-LPME) followed by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The pK_a and log D of DPAs were determined by curve-fitting the experimental data with equations derived on the basis of the Henderson-Hasselbalch equation and compared with model calculated data. For MEPA, DEPA and MHPA, the pK_a values were close and around 3, but the log Ds were strongly pH-dependent with values from -5.01 to 1.01. The log K_OW of the neutral form (logK_OW,HA) and ionic form (logK_OW,A) were in the range of -0.67-1.02 and -3.86--1.33, respectively. The experimentally determined pK_a values were highly in good agreement with ACD/pK_a predicted values and the measured log K_OW,HA values were closely related to KOWWIN calculated ones, suggesting ACD/pK_a and KOWWIN are good alternative methods to estimate pK_a and log K_OW of DPAs, respectively. As far as we know, this is the first report on the pK_a and log D data for DPAs, which are fundamental for the product design and evaluating the environmental behavior and effects of DPAs and ADPs.

High-Throughput Determination of Octanol-Water Partition Coefficients by Ultrasound-Assisted Liquid-Phase Microextraction

A method of high-throughput determination, which is based on ultrasound-assisted liquid-phase microextraction, was developed to measure directly the partition coefficients of n-octanol-water. In ultrasound-assisted liquid-phase microextraction, ultrasonic energy can facilitate the mass transfer process of six or more microextractors simultaneously. Therefore, high-throughput determination of n-octanol-water partition coefficients can be performed favorably, and the equilibrium time of each microextractor can be decreased effectively. Several experimental parameters including ultrasonic power and frequency, centrifugation conditions, extractant volume and sample concentration were analyzed and optimized at 25°C. Under the optimum conditions, it only takes 2 min to reach extraction equilibrium, and the solutions of sample can be separated by centrifugation in 4 min. After centrifugation, the concentrations in n-octanol phases are analyzed with gas chromatography. The method was further evaluated with eight reference compounds and the findings demonstrated that this method is suitable to determine the partition coefficients of organic compounds accurately and quickly. Next, the method was exploited to measure the partition coefficients of n-octanol-water containing 20 organic compounds, which cover the [Formula: see text] values from 0.05 to 4.36, with comparatively low relative standard deviation (RSD) directly. The results of this study illustrated that the RSD (n = 6) was under 3%.

The development of a high-throughput measurement method of octanol/water distribution coefficient based on hollow fiber membrane solvent microextraction technique

This paper describes the development of a novel high-throughput hollow fiber membrane solvent microextraction technique for the simultaneous measurement of the octanol/water distribution coefficient (logD) for organic compounds such as drugs. The method is based on a designed system, which consists of a 96-well plate modified with 96 hollow fiber membrane tubes and a matching lid with 96 center holes and 96 side holes distributing in 96 grids. Each center hole was glued with a sealed on one end hollow fiber membrane tube, which is used to separate the aqueous phase from the octanol phase. A needle, such as microsyringe or automatic sampler, can be directly inserted into the membrane tube to deposit octanol as the accepted phase or take out the mixture of the octanol and the drug. Each side hole is filled with aqueous phase and could freely take in/out solvent as the donor phase from the outside of the hollow fiber membranes. The logD can be calculated by measuring the drug concentration in each phase after extraction equilibrium. After a comprehensive comparison, the polytetrafluoroethylene hollow fiber with the thickness of 210 μm, an extraction time of 300 min, a temperature of 25 °C and atmospheric pressure without stirring are selected for the high throughput measurement. The correlation coefficient of the linear fit of the logD values of five drugs determined by our system to reference values is 0.9954, showed a nice accurate. The -8.9% intra-day and -4.4% inter-day precision of logD for metronidazole indicates a good precision. In addition, the logD values of eight drugs were simultaneously and successfully measured, which indicated that the 96 throughput measure method of logD value was accurate, precise, reliable and useful for high throughput screening.

Liquid-phase microextraction with porous hollow fibers, a miniaturized and highly flexible format for liquid–liquid extraction

Since 1999, substantial research has been devoted to the development of liquid-phase microextraction (LPME) based on porous hollow fibers. With this technology, target analytes are extracted from aqueous samples, through a thin supported liquid membrane (SLM) sustained in the pores in the wall of a porous hollow fiber, and further into a microL volume of acceptor solution placed inside the lumen of the hollow fiber. After extraction, the acceptor solution is directly subjected to a final chemical analysis by liquid chromatography (HPLC), gas chromatography (GC), capillary electrophoresis (CE), or mass spectrometry (MS). In this review, LPME will be discussed with focus on extraction principles, historical development, fundamental theory, and performance. Also, major applications have been compiled, and recent forefront developments will be discussed.