Sequential injection extraction based on restricted access material for determination of furosemide in serum

Centrifuged and diluted serum sample was aspirated into the system and loaded onto the column using acetonitrile-water (2:98), pH 2.7. The analyte was retained on the column while proteins contained in the sample were removed to the waste without precipitation and clogging the column. Interfering substances complicating the detection were washed out by acetonitrile-water (15:85), pH 2.7 in the next step. The extracted analyte was eluted by means of acetonitrile-water (25:75), pH 2.3 to the fluorescence detector (emission filter 385 nm). The whole procedure comprising sample pre-treatment, analyte detection and column reconditioning took 20 min. The recoveries of furosemide from serum lay between 101.4 and 103.4% for three concentrations of analyte.