Determination of oxolinic acid in cowʹs milk and human urine by means of a single-use phosphorimetric sensor

A single-use phosphorimetric drop plane sensor for the determination of oxolinic acid (OXA) is proposed. The sensor was formed by a 30×16 mm2 rectangular strip of Mylar type polyester as solid support that contained a circular sensing zone, 6 mm in diameter and 20 μm in thickness, formed by PVC plasticized with tributylphosphate adhered to its surface. When the strip was introduced for 1 hour into a sample solution, the analyte was retained in the sensing zone, making it possible to directly measure the phosphorescence intensity emitted by the OXA in the solid phase, at λexc=330 nm and λem=449 nm. The variables that affect the construction of the sensor have been studied, along with the experimental variables that influence the fixation of the analyte in the sensor. The methodʹs detection limit was 0.01 mg l−1 with an applicable concentration range from 0.04 to 1.50 mg l−1 and a repeatability of 2.6% at the concentration range of 0.8 mg l−1. The method was applied to samples of human urine and cowsʹ milk, with recovery percentages ranging between 97.6 and 108.7%.