Estimation of log Pow values for neutral and basic compounds by microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (μMEEKC-IFD)

Microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (μMEEKC-IFD) was used to obtain log P octanol/water (log Pow) values for neutral and basic compounds. Six compounds, with log Pow values between 0.38 and 5.03, were used to create a calibration curve relating the log of retention factors (log k) obtained from μMEEKC-IFD with the known log Pow values. The log Pow values for six additional compounds were determined using the log k values obtained by μMEEKC-IFD and the linear relationship between log Pow and log k established for the standard compounds. The μMEEKC-IFD buffer was composed of 50 mM 3-[cyclohexylamino]-1-propane-sulfonic acid (CAPS) buffer (pH 10.4) containing 1.2% n-heptane (v/v), 2% sodium dodecylsulfate (w/v), 8% 1-butanol (v/v) and 4 μM 5-carboxytetramethyl-rhodamine (TAMRA) as the fluorophore probe for indirect detection. The μMEEKC-IFD provided an accurate method for estimating log Pow values and also a means for analyzing compounds that are non-fluorescent.