OIL-IN-WATER MICROEMULSIONS AS MOBILE PHASES FOR RAPID SCREENING OF ILLEGAL DRUGS IN SPORTS

Microemulsions are clear, stable and spontaneously forming liquid disperse systems. They contain an oil, water, a surfactant and a cosurfactant. The system heptane, water, sodium dodecylsulfate (SDS) and n-pentanol was used. The mass diagram was determined. Water rich compositions of the oil-in-water microemulsion type (L1) were investigated as mobile phase in reversed phase liquid chromatography with a 5 mum C18 bonded stationary phase column. The solutes were 11 drugs illegally used in sport. It is shown that the solute retention decreases when the organic content, phi, of the microemulsion (heptane + active blend: SDS and pentanol) increases. A linear relationship between k' and log phi was found. The selectivity becomes nil, all solutes having the same k' = 0.5 value, when the microemulsion organic content was 15.2% (+/- 0.5% v/v). The active blend (SDS/pentanol) and heptane play a similar role on retention. They have an opposite effect on efficiency. The solute mass transfer increased with the active blend content. It dramatically decreased when the microemulsion heptane content increased. However, heptane decreased the protein peak width when urine samples were directly injected. The limit of detection of the drug tested was in the nanogram injected range.