Desenvolvimento de um fotômetro com fins didáticos

Abstract

In this work was developed a photometer for didactic purposes for use in the context of social themes chemicals, such as environmental chemistry and classes of analytical instrumentation, with total determination of total orthophosphate in water. The instrument was developed using cheap materials and easy disposal. The instrument consists of a yellow LED and LDR; the first is the source and the former the detector. The signal of the photometer is available by values in resistivity, within is measured with assistance of the digital multimeter. For the determination of the orthophosphate was used the Molybdenum Blue Colorimetric Method, using river waters as test samples. Procedures for analytical validation tests were for the most suitable configuration, choosing a bucket acrylic, range from 200 kW resistivity and use of cover to the apparatus, as well as checking the stability of the source. Accuracy, precision, recovery and linearity of the photometer were checked. The repeatability and intermediate precision had coefficients of variation average 3.0 and 2.8, respectively. Accuracy was examined with statistical comparison based upon test F and t for p < 0.05, with same measures evaluated in the photometer and spectrophotometer UV-Vis, for comparison. With 95% confidence level was revealed that there are significant differences between the values of concentration, and the results were satisfactory with the use of a correction factor The recovery tests were satisfactory, with variations between 97.6 and 107.3%. The linearity is satisfactory in the range 8-48 μmol l-1, with r2 values above 0.99.