Determination of alkylphosphonic acids using micellar electrokinetic chromatography with laser-induced fluorescence detection and high-salt stacking

Methyl-, ethyl- and propylphosphonic acids (MPA, EPA, and PPA, respectively) were derivatized with panacyl bromide in dry N,N-dimethylformamide (DMF). After mixing with a high-salt dilution buffer, the derivatives were separated by micellar electrokinetic chromatography in 35 min and detected by laser-induced fluorescence (He–Cd laser excitation at 325 nm and detection at 500 nm). Baseline resolution was achieved using a separation buffer containing 50 mM sodium cholate, 40% (v/v) of acetonitrile and 50 mM borate. Addition of 400 mM NaCl to the dilution buffer allowed the injection time to be increased to 30 s while still maintaining baseline resolution. Limits of detection for MPA, EPA, and PPA were 0.13 μM (12 ppb), 0.13 μM (14 ppb) and 0.14 μM (17 ppb) injected, respectively. The reproducibility of corrected peak area at 15 μM was 3.7∼4.3%.