Potencialidades das técnicas com fonte de plasma e da espectrometria de absorção atômica em forno de grafite de alta resolução com fonte contínua para análise de fertilizantes
Machado, Raquel Cardoso
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Each year, Brazil sets records on agricultural productivity, which significantly increases the use of fertilizers in crops to provide the essential nutrientes. However, fertilizers can also be sources of toxic elements from the raw material and manufacturing processes, which can be absorbed by crops. In this thesis, different strategies were adopted to the development of analytical methods employing tniques with plasma sources, as microwave induced plasma optical emission spectrometry (MIP OES) and inductively coupled plasma mass spectrometry with a tandem mass configuration (ICP-MS/MS), and direct solids analysis using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) for fertilizers analysis, overcoming spectral and non-spectral interferences. The hydride generation coupling to MIP OES (HG-MIP OES) favored the determination of As, Bi, Ge, Sb, and Sn in fertilizer samples, with recovery of 106 % for As obtained from the certified reference material (CRM) NIST 695 and recoveries between 90 and 118 % from addition and recovery experiments. Silicon in fertilizers was determined by MIP OES using air addition into the N2 plasma after microwave-assisted digestion in acid and alkaline médium. The air addition into the N2 plasma render it more robust against the addition of electrons in the plasma due to the presense of Na, which is easily ionizable. The Si results obtained by MIP OES were compared with reference values obtained by X-ray fluorescence (XRF) and inductively coupled plasma optical emission spectrometry (ICP OES). The recoveries between 80 and 89 % without and 97 and 100 % with air addition were obtainde, respectively. In another study, a multi-energy calibration method (MEC) with matrix-matching capability was evaluated for fertilizer analysis by MIP OES. This strategy was effective for determination of As, Cd, Ba, Cr and Pb in mineral fertilizers, whose recoveries ranged from 96 to 101 % in fertilizer reference material (NIST 695) for As, Ba, Cr, and Pb and from 92 to 105 % for Cd in addition and recovery experiments in fertilizer samples. In fertilizers analysis by ICP-MS/MS, free-interference determinations were obtained for Cd and Sn, and for platinum group metals, such as Pd, Pt, and Rh, Rhodium and Pt were determined from the mode MS/MS mass-shift and Cd, Pd, and Sn were determined from the mode MS/MS on mass. To evaluate the accuracy, addition and recovery experiments at three concentration levels were performed and recoveries between 81 and 102 %, and 80 to 113 % were obtained for the MS/MS mass-shift mode and MS/MS on mass, respectively. Direct analysis of fertilizers solids was proposed for the simultaneous determination of Co, Cr, Fe, and Ni by HR-CS GFAAS, using in situ microfusion procedure to matriz elimination. The monitoring of the spectral region around the wavelength 298.560 nm allowed simultaneous determination of analytes, employing aqueous solutions for calibration. Applying the method developed, recoveries ranged from 81 and 120 % were obtained for direct analysis of CRM NIST 695.