Determination of 4-Methylpropranolol in Cerebrospinal Fluid, Serum, and Urine by Nonprotected Fluid Room-Temperature Phosphorescence Using Simplex Optimization

A direct and simple procedure for the determination of 4-methylpropranolol, a specific β-adrenergic receptor blocking agent, in biological fluids was developed. The method was based on the measurement of the nonprotected fluid room-temperature phosphorescence of the drug. This technique enables us to determine analytes in complex matrices without the need for a tedious prior separation process. The appropriate experimental conditions to obtain suitable reproducibility and maximum phosphorescence signal, when sodium sulfite is used to eliminate the oxygen from the solution and when potassium iodide is used as heavy atom, were studied. The optimum concentration of KI was 3.2 M. The optimization of Na2SO3 (7.0 × 10−3 M) and the accurate value of pH (10.88) were determined using a simplex as the method of optimization. A sodium carbonate–hydrogen carbonate buffer solution (5.0 × 10−2 M) was used to adjust the value of pH. The delay time (124 μs), gate time (206 μs), and time between flashes (5 ms) were also optimized using a simplex. Under the above conditions, the maximum signal of phosphorescence appears instantly once the sample has been prepared, and the intensity was measured at λex = 300 nm and λem = 537 nm, in the concentration range 25–500 ng/ml. Overall least-squares regression was used to find the straight line that fit the experimental data. The detection limit according to the error propagation theory was 6.2 ng/ml and the detection limit calculated as proposed by C. A. Clayton et al. (1987, Anal. Chem. 59, 2506) was 11.7 ng/ml. The repeatability was studied using 10 solutions of 200 ng/ml 4-methylpropranolol; if error propagation theory was assumed, the relative error was 1.78% and the standard deviation for replicate samples was 3.5 ng/ml. This method was successfully applied to the determination of 4-methylpropranolol in urine, serum, and cerebrospinal fluid, with recoveries of 99.3 ± 0.5% in the case of urine, 99.8 ± 0.2% for serum, and 101.5 ± 1.5% for cerebrospinal fluid.