In this work, analytical approaches for the selective determinations of cyclofenil, stroblilurins (azoxystrobin and dimoxystrobin) and Cu (II) have been developed. The determination of cyclofenil was made by taking advantage of their fluorescent photoderivative. In order to achieve maximum fluorescence (250/410), the best conditions for derivatization and for the analytical measurements have been optimized firstly by univariate approach and then by a multivariate way (central composite design). The optima conditions were: 2 h of UV exposition time and solvent system composed by methanol/Britton-Robinson buffer pH 10.5. A mechanism for this photochemical reaction has been proposed, with the indication of the structure of two most probable photoderivades. In such conditions, the analytical response presented a linear and homocedastic behavior (r2=0,9951) up to 8 x 10-5 mol L-1. Limit of detection (LQ) and limite of quantification (LQ) for the spectrofluorimetric determination were respectively 1.1 x 10-8 mol L-1 and 3.,7 x 10-7 mol L-1. The methodology was proven to be adequate to quantify cyclofenil in pharmaceutical formulations with mean recovery of 98.3 + 3.9%. For the determination of cyclofenil in urine, it was necessary the use of a separation technique (HPLC). In such case, the fluorescent signal from one of its photochemical derivatives (7.0 min retention time) was chosen. Efficient separation from the matrix background was achieved using a C- 18 column, gradient elution using methanol/water system. The use of an internal standard (m-toluil acetate) allowed recoveries of 99.5 + 3.4 % for cyclofenil fortified urine samples. In the case of the selective anodic stripping voltammetric determination of Cu (II) using bismuth film electrode, the overlapping between Cu (II) and Bi (III) needed to be eliminated, since both species present redissolution peaks near +80 mV. The interference was solved by the addition of PUC-Rio - Certificação Digital Nº 0410388/CA hydrogen peroxide in the working cell which caused the shifting of Cu (II) redissolution peak to +200 mV, probably caused by the deposition of oxidated copper species on the electrode surface. The experimental and instrumental conditions have been optimized in an univariated way in order to achieve a maximum analytical signal for Cu (II). As a result, the optimized conditions were: -1400 mV of deposition potential, 400 mV s-1 scan rate, 100 mV amplitude. In such conditions, a linear and homoscedastic behavior (r2 = 0,9927) analytical response was found. The method has been applied for sugarcane spirit samples where values of 2.9 x 10-7 mol L-1 and 9.5 x 10-7 mol L-1 were achieved respectively for LD and LQ. The results from such determinations had been compared with the ones from another technique (graphite furnace atomic absorption spectrometry) with statistically similar results. The simultaneous determination of Cd (II) and Pb (II) was also achieved using a compromised condition. For the strobilurins, a sensible and selective voltammetric method was developed to be applied in foods, river water and industrial juices. The experimental conditions have been developed in order to achieve a maximum analytical signal for the simultaneous determination of azoxistrobin and dimoxistrobin in the hanging mercury drop electrode. The optimized conditions were: deposition potential at -300 mV, 150 mV amplitude, 300 mVs-1 using the square wave mode. In such conditions, the azoxystrobin and the dimoxystrobin peaks were found at – 928 mV and -650 mV respectively. Linear analytical response (r2>0,99) and homoscedastic behavior have been observed. LD and LQ where respectively 3.6 x 10-7 mol L-1 and 1,2 x 10-6 mol L-1 for azoxystrobin and 7.1 x 10-7 mol l-1 and 2.4 x 10 -6 mol L-1 for dimoxystrobin. Enough selectivity was achieved in complex samples and no interferences from others strobilurins (piraxystrobin and picoxystrobin) was found. A simple mechanism for the redox process at the mercury electrode was proposed.