Experimental design methodologies to optimise the spectrofluorimetric determination of Losartan and Valsartan in human urine

A spectrofluorimetric method has been developed for the determination of two angiotensin II receptor antagonists (ARA II): Losartan and Valsartan. A fractional factorial design and a central composite design were used. The key factors considered in the optimization process were pH, temperature and emission slit width. Maximum fluorescent intensity was established as response for each experiment. The response surfaces confirmed the robustness of the method. A clean-up procedure was used for urine samples that consisted of a solid-phase extraction using C8 cartridges. The total analysis time was lower than 30 min. This method proved to be accurate (RE, 8%), precise (intra- and inter-day coefficients of variation were lower than 8% and sensitive enough (LOQ c.a. 0.5 μg ml⁻¹) to be applied to the determination of Losartan and Valsartan in urine samples.     

Speckle statistics in partially corrected wave fronts

Wave fronts distorted by the atmosphere preserve high-spatial-frequency information. This information can be retrieved by use of adaptive optics systems to correct the incoming wave front. This correction should be as nearly complete as possible. In experiments performed in the visible, only partial compensation is attainable. We provide a theoretical model to predict the intensity statistics of the light in the image center as a function of the number of Zernike polynomials corrected.     

Conservative methods for the Toda lattice equations

We are concerned with the numerical integration of the Todalattice equations by using different conservative methods. Numericalexperiments suggest that the global error for isospectral schemesdecreases exponentially with time but it is almost constantfor either symplectic or more general integrators. We providea theoretical explanation for these experimental findings.