Desenvolvimento e validação de métodos analíticos para quantificação de ferro total em sedimentos de fundo por imagem digital

Abstract

In recent years, the new trend in the development of portable, low cost and fast methods has been growing. Thus, the combination of colorimetric reactions with digital image analysis has been widely explored. In this context, this study presents a novel method for iron determination by the combination of spot test and digital image analysis. The methods are based on the colorimetric spot test reaction of the analyte with ortho-phenanthroline and thiocyanate. Digital images were acquired using a flatbed scanner and converted to RGB values in Matlab software. According to the results, both analytical methods showed linear responses in the 2.0 – 10.0 mg L-1 range using the G channel. The method developed with the ortho-phenanthroline showed a limit of detection (LOD) and quantification (LOQ) equal to 0.33 and 1.11 mg L-1, respectively. Similar values were obtained for the method developed with thiocyanate (LOD = 0.29 mg L-1 and LOQ = 0.96 mg L-1). The accuracy of the methods was checked by analyzing certified reference material (CRM) (NIST 8704) and the results agreed at a confidence level of 95%. The methods were applied in the analysis of twelve samples of bottom sediment and the results were compared with those obtained by inductively coupled plasma optical emission spectrometry (ICP OES). The results show good agreement, with relative error values within 10%.