Study of the uncertainty in gravimetric analysis of the Ba ion

The determination of barium by the gravimetric method, in which the precipitation of BaSO4 was formed and weighed, coupled with instrumental measurement of trace constituents was studied. The analyte’s remaining in the filtrate and washes, mechanical loss, contaminants in the precipitate are the main influencing factors of uncertainty. A series of condition tests have been done, to reduce the effect of the factors mentioned above and the optimum test condition was found. The determination was carried out with a strictly defined operational procedure. The trace amounts of barium in the filtrate, washes and mechanical loss were determined by ICP-AES, the chloride occluded in the precipitate was determined by ion chromatography (IC), calculated as BaCl2 and barium, and sodium by FAAS, calculated as Na2SO4. The average mass of barium in the filtrate contributes about 0.06% relative to that of the total barium, in washes about 0.09%, mechanical loss about 0.06%, contaminants of BaCl2 about 0.08% and Na2SO4 about 0.05%. All the trace constituents were determined and corrected on a sample-by-sample basis. Sources of uncertainty were assessed thoroughly. The uncertainty of this combined gravimetric-instrumental method was improved remarkably compared with that of gravimetric method alone. The expanded uncertainty (k =2) is 0.08%.