Resumen

CORI CONDORI, Delia M. et al. Optimización del método de digestión ácida en sistema de microondas para la determinación de concentraciones pseudo-totales de Fe, Mn y Zn en sedimentos de la cuenca Katari bajo, La Paz, Bolivia. Rev. Bol. Quim [online]. 2021, vol.38, n.5, pp.13-27. ISSN 0250-5460.  https://doi.org/10.34098/2078-3949.38.5.2.

The sediments are considered reservoirs of trace elements where these are transported by river water and deposited in the lower part of the basin. The work presents the optimization of an acid digestion method in a microwave system to determine trace elements like Fe, Mn and Zn in sediments at three depths, PK9-1 (0-0.5 m), PK9-2 (0.5-2 m) and PK9-3 (2-2.7 m) in a randomly selected piezometer from a total of 17 piezometers. In addition, certified reference materials as the MRC MESS-3 for sediments and the MRC C17-2 for soils have been used for a quality control of the acid digestion method. For the quantification, the Flame Atomic Absorption Spectrometry (FAAS) technique has been used and for the statistical interpretation of the data, a 2x2 factorial design (ANOVA) was applied. The extraction procedures involve volume variations of 3:3 and 3:1 mL of HNO3:HCl, a power of 300/600 W and 100/300/700 W and with/without the use of H2O2. The result of the MRC MESS-3 shows that varying the extraction conditions does not considerably affect the concentrations of Fe, Mn and Zn, where the most optimal procedure is 3 hours, without H2O2 and with 3:1 mL HNO3/HCl with a minimum significant difference between the experimental and the reference values. The results using the MRC C17-2 show errors that exceed 10% where there are significant differences between the experimental and reference value for Zn and Mn. On the other hand, PK9-1 (0-0.5) m and PK9-3 (0.5-2) m show P > 0.05 for Fe, indicating a significant difference in the average concentrations, and P < 0.05 for Zn/Mn indicating that there are no significant differences in the average concentrations when varying the volume and power conditions. Likewise, PK9-2 (0.5-2) m shows P > 0.05 for Zn/Fe, indicating a significant difference in the average concentrations when varying the conditions of volume, power and with/without the use of H2O2. For Mg, a P < 0.05 indicates that there is no significant difference in the average concentrations. Therefore, varying amounts of volume, power and H2O2 do not considerably alter the trace elements concentrations and therefore the trace elements concentrations vary with depth according to the lithological characteristics of the sediments.

Palabras clave : Trace Elements; Microwave System; Acid digestion; Sediments.

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