Direct determination of naftopidil by non-protected fluid room temperature phosphorescence

Abstract

A selective and sensitive room temperature phosphorimetric method for the direct determination of naftopidil in biological fluids is described. The method is based on obtaining a phosphorescence signal from this antihypertensive drug using TlNO₃ as a heavy atom perturber and Na₂SO₃ as a deoxygenator agent without a protective medium. This technique is named non-protected room temperature phosphorescence (NP-RTP), and enables us to determine analytes in complex matrices without the need for a tedious prior separation process. The optimization of Na₂SO₃ (8.5 × 10⁻³ Mmethod of optimization. Sodium carbonate–hydrogencarbonate buffer solution (5.0 × 10⁻² M) was used to adjust the suitable pH. The optimum concentration of Tl⁺ (8.5 × 10⁻² M) was also determined. The delay time, gate time and time between flashes selected were 200 μs, 200 μs and 5 ms, respectively. Under the above conditions we propose a method to determine naftopidil by direct measurement of phosphorescence intensity with an emission wavelength of 526 nm and an excitation wavelength of 296 nm in the concentration range 0.05–1.00 mg L⁻¹. Under these conditions the phosphorescence signal appears in 3 min once the sample has been prepared. Optimization of the various conditions permitted the establishment of an NP-RTP method for the determination with a detection limit, according to the error propagation theory, of 21.0 ng mL⁻¹. The repeatability was studied using 10 solutions of 0.20 mg L⁻¹ of naftopidil; if error propagation is assumed, the relative error is 1.39%. The standard deviation for replicate samples was 1.1 × 10⁻² mg L⁻¹. This method was successfully applied to the determination of naftopidil, in human urine with recoveries between 106 and 112%.