Common Problems with Ag, As, S, Ba, Pb and Cr

Barium (Ba)

Of the four acids most commonly used in sample preparations, Ba will form precipitates with HF and H₂SO₄. In addition, the solubility of BaHPO₄ and BaCrO₄ are 0.01 and 0.001 g/100 g H₂O respectively. Solutions that are neutral or alkaline will ppt. BaCO₃ (solubility 0.0024 g/100g H₂O).

• Samples containing Ba and sulfur compounds may form BaSO4 in oxidative decompositions. I know of no simple way to dissolve this precipitate. Since small amounts of barium sulfate do not readily coagulate the precipitate can easily go unnoticed. Attempts to dissolve barium sulfate have seemingly focused upon the use of EDTA (K_f 7.86) and DTPA (K_f 8.78). However, the pH of the solution, which must be ~ 5, can lead to precipitation and/or adsorption problems with other analytes and the dissolution rate is slow.
• Avoid combinations of Ba⁺² with SO4⁼, CrO4⁼ or F^-1 in acidic media.
• Avoid raising the pH of sample solutions containing Ba⁺² to 7 or greater to avoid loss as the carbonate or hydrogen phosphate.

• Ba elemental data

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