Direct determination of naftopidil by non-protected fluid room temperaturephosphorescence

A selective and sensitive room temperature phosphorimetric method for the d irect determination of naftopidil in biological fluids is described. The me thod is based on obtaining a phosphorescence signal from this antihypertens ive drug using TlNO3 as a heavy atom perturber and Na2SO3 as a deoxygenator agent without a protective medium. This technique is named non-protected r oom temperature phosphorescence (NP-RTP), and enables us to determine analy tes in complex matrices without the need for a tedious prior separation pro cess. The optimization of Na2SO3 (8.5 x 10(-3) Mx 10(-2) M) was used to adj ust the suitable pH. The optimum concentration of Tl+ (8.5 x 10(-2) M) was also determined. The delay time, gate time and time between flashes selecte d were 200 mus, 200 mus and 5 ms, respectively. Under the above conditions we propose a method to determine naftopidil by direct measurement of phosph orescence 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 th ese conditions the phosphorescence signal appears in 3 min once the sample has been prepared. Optimization of the various conditions permitted the est ablishment 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 repeata bility was studied using 10 solutions of 0.20 mg L-1 of naftopidil; if erro r propagation is assumed, the relative error is 1.39%. The standard deviati on for replicate samples was 1.1 x 10(-2) mg L-1. This method was successfu lly applied to the determination of naftopidil, in human urine with recover ies between 106 and 112%.