Comparison of some methods for determination of sulfate in soils |
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| Abstract: | Abstract Sulfate (SO4 2‐) is present in soils as salts of various metals, and the different metals associated with sulfate may influence adsorption of SO4 2‐by soils. The analytical method used for determination of SO4 2‐could be affected by the type of metal associated with the SO4 2‐. Four analytical methods based on different principles were evaluated for determination of SO4 2‐in different metal salts and in soil extracts obtained with three extractants {0.1M lithium chloride (LiCl), 0.15% calcium chloride (CaCl2), and 500 mg P/L as calcium phosphate Ca(H2PO4)2]}. The analytical methods were: (i) a methylene blue (MB) colorimetric method after the reduction of SO4 2‐to hyrogen sulfide (H2S), (ii) an ion Chromatographie (IC) method, (iii) a turbidimetric (TD) method, and (iv) an indirect barium (Ba) atomic absorption spectrophotometric (SP) method. The recovery of SO4 2‐associated with various mono‐, di‐, and tri‐valent metals was quantitative by the MB method. But, trivalent metals, such as aluminum (Al), indium (In), lanthanum (La), and scandium (IC), decreased the recovery of SO4 2‐by the other three methods. The MB and IC methods gave similar values for SO4 2‐in soils by using the three extractants. The TD and SP methods gave variable results and, in general, underestimated the amounts of SO4 2‐in soils. Among the four methods, the MB and IC methods were the most accurate and precise. |
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