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Tubino, Matthieu; Queiroz, Carlos A.R. Flow injection visible diffuse reflectance quantitative analysis of total sulfur in biodiesel, in plant leaves and in natural waters Eclética Química, vol. 34, núm. 2, 2009, pp. 29-36 Universidade Estadual Paulista Júlio de MesquitaFilho Brasil
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Eclética Química ISSN (Versión impresa): 0100-4670 atadorno@iq.unesp.br Universidade Estadual Paulista Júlio de Mesquita Filho Brasil

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www.scielo.br/eq Volume 34, número 2, 2009

Flow injection visible diffuse reflectance quantitative analysis of total sulfur in biodiesel, in plant leaves and in natural waters
Matthieu Tubino*, Carlos A.R. Queiroz
Institute of Chemistry, State University of Campinas CP 6154, CEP 13083-970 Campinas, SP, Brazil

Abstract: Flow injection (FI) methodology, usingdiffuse reflectance in the visible region of the spectrum, for the analysis of total sulfur in the form of sulfate, precipitated in the form of barium sulfate, is presented. The method was applied to biodiesel, to plant leaves and to natural waters analysis. The analytical signal (S) correlates linearly with sulfate concentration (C) between 20 and 120 ppm, through the equation S= 1.138+0.0934 C(r = 0.9993). The experimentally observed limit of detection is about 10 ppm. The mean R.S.D. is about 3.0 %. Real samples containing sulfate were analyzed and the results obtained by the FI and by the reference batch turbidimetric method using the statistical Student’s t-test and F-test were compared. Keywords: diffuse reflectance; solution; sulfur; sulfate; biodiesel; plant leaves; waterIntroduction When compared, for example, with those methods that use transmittance (absorbance), reflectance quantitative analytical methods in the UV–Vis region are not very popular. This fact can be attributed, in part, to the difficulty in preparing rigorously homogeneous reflecting surfaces. However, despite this problem, several quantitative reflectometric methods for the determination of analytesimmobilized on solid supports have been developed offering quite good results [1–10]. It is also possible to work in solution, measuring the diffuse reflectance of solids suspended in liquids [1-2, 8]. Turbidimetry and nephelometry are closely related analytical techniques based on the scattering of radiation by a solution containing dispersed particulate matter. When a radiation passes through atransparent medium in which solid particles are dispersed, part of the radiation is scattered in all directions, giving a turbid appearance to the mixture. Turbidimetry is based on the meaEcl. Quím., São Paulo, 34(2): 29 - 36, 2009

suring of the intensity of the radiation transmitted by the solution whereas nephelometry is based on the scattered radiation at an angle, usually at the right angle.Turbidimetry is usually applied in the cases of concentrated particulates dispersed in solution whereas nephelometry is based on the scattered radiation at an angle, usually at the right angle. Turbidimetry is usually applied in the cases of concentrated particulates dispersed in solution while nephelometry offers reliable results at low concentrations because a small scattering intensity againsta black background is easier to measure than a small change in intensity of intense transmitted radiation. The intensity of radiation appearing at any angle depends upon the number of particles, their size and shape, as well as the wavelength of the radiation [11]. If the light reflected out of the plane of incidence of the radiation is considered the phenomenon it can be considered as diffuse...
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