Abstract: An extraction system consuming less than 1 µl of sample and organic solvent (combined volume) has been developed for the determination of 1-octanol-water partition coefficients (log K-ow). The system comprises a capillary, a micro-volume stepper piston pump, a peristaltic pump and a detector. The stepper piston pump is programmable, enabling full control and selection of each step in the pumping sequence. Coupled to the pump is a 250 µm i.d. silica capillary, extending 240 mm from its aperture to the detector cell which houses an on-capillary spectrophotometric detector allowing direct monitoring of both the aqueous sample and the organic solvent plugs. Programmed portions of air, aqueous sample, organic solvent and a second portion of air are sequentially introduced into the capillary from respective vials. Typically, 250 nl of both the aqueous sample and organic solvent were introduced in the trials reported here. Since all liquids are aspirated directly into the capillary there is no need to pre-flush the system (as is required in most other continuous flow systems). Thus, the entire portions of the sample and the organic solvent are used in the analysis. The analytical procedure used for determining octanol-water partition coefficients is essentially an automated and miniaturised version of the batch method recommended in the OECD manual. The log K-ow values obtained agreed well with literature data and/or manual batch determinations. Typical analysis time was 4 min when applying a mean flow rate of about 4 µl min-1, including a wash cycle between the samples. The system is suitable for screening purposes and could readily be automated using a robot.

Abstract: Single-channel coaxial segmenters were used for the introduction of an aqueous or octan-1-ol solution of an organic substance directly into a continuous flow of the other solvent. The analytical signal was measured simultaneously on both aqueous and organic phase segments by an 'on-tube' fast-reading spectrophotometric detector (ca. 3 ms time resolution) and treated mathematically. The octan-1-ol-water phase signal ratio corresponds to the partition coefficient of the organic substances. The applicability of the method is demonstrated by the determination of partition coefficients of phenol, citric acid, acetylsalicylic acid and sodium salicylate.

Abstract: A block diagram for the flow injection method is shown. The supporting electrolyte solution (usually 0.1 M KCl), from which O is removed, is placed in the reservoir. An active charcoal column is placed between the peristaltic pump and the injection valve to remove traces of surfactants dissolved in the supporting electrolyte solution. The most important part of the app. is the voltammetric cell, which is made from a Teflon cylinder in which a hanging Hg drop electrode, a calomel electrode, and a Pt electrode are placed. Surfactants are introduced via the injection valve and differential-capacitance-time (C vs. t) curves are measured in the voltammetric cell. The decrease in differential capacitance shows the adsorption of the surfactant. The C vs. t curves for Hg at -0.6 V in 0.1 M KCl with and without additions of saturated n-octyl alcohol and vitamin B12 are shown. The adsorption of the n-octyl alcohol is reversible while that of vitamin B12 is not.