Ha. Ajwa et Ma. Tabatabai, COMPARISON OF SOME METHODS FOR DETERMINATION OF SULFATE IN SOILS, Communications in soil science and plant analysis, 24(15-16), 1993, pp. 1817-1832
Sulfate (SO42-) is present in soils as salts of various metals, and th
e different metals associated with sulfate may influence adsorption of
SO42- by soils. The analytical method used for determination of SO42-
could be affected by the type of metal associated with the SO42-. Fou
r analytical methods based on different principles were evaluated for
determination of SO42- in different metal salts and in soil extracts o
btained with three extractants {0.1M lithium chloride (LiCl), 0.15% ca
lcium chloride (CaCl2), and 500 mg P/L as calcium phosphate (Ca(H2PO4)
2]}. The analytical methods were: (i) a methylene blue (MB) colorimetr
ic method after the reduction of SO42- to hyrogen sulfide (H2S), (ii)
an ion chromatographic (IC) method, (iii) a turbidimetric (TD) method,
and (iv) an indirect barium (Ba) atomic absorption spectrophotometric
(SP) method. The recovery Of SO42- associated with various mono-, di-
, and trivalent metals was quantitative by the MB method. But, trivale
nt metals, such as aluminum (Al), indium (In), lanthanum (La), and sca
ndium (IC), decreased the recovery Of SO42- by the other three methods
. The MB and IC methods gave similar values for SO42- in soils by usin
g the three extractants. The TD and SP methods gave variable results a
nd, in general, underestimated the amounts of SO42- in soils. Among th
e four methods, the MB and IC methods were the most accurate and preci
se.