Determination of the pK(a) of 12-S-hydroxyheptadecatrienoic acid by studies of its vial surface adsorption using high-performance liquid chromatography and liquid scintillation technique.

H John, W Schlegel

Index: Chem. Phys. Lipids 99(1) , 95-101, (1999)

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Abstract

When dissolving 12-S-hydroxyheptadecatrienoic acid (HHT) in aqueous buffer systems, a partition equilibrium is achieved between the liquid buffer phase and the solid vial phase. This adsorption equilibrium is dependent on the vial material, the ratio of solvent volume to moistened vial surface area (V/A), the pH of the aqueous solution the buffer additives and the contact time. Partition ratios (E) were established following determination of the recoveries (omega) of HHT in the liquid phases. The pK(a) of HHT could be calculated to be 4.4 +/- 0.2. The HHT concentration in the liquid phase rose considerably when increasing the pH value (17% at pH 1.9, up to 97% of applied HHT at pH 8.0) and increasing the V/A-ratio, as well as when using glass instead of polypropylene (PP) or adding acetonitrile as an organic solvent and HHT-affine substances like albumins or globulin. The HHT concentration was found to decrease during contact to PP surfaces as a result of HHT adsorption and diffusion into the hydrophobic vial material. This effect could be minimized by adding a larger percentage of acetonitrile (50-60%).