Unsuitability of porcelain crucibles for dry ashing of biological tissues for calcium analysis.

At temperatures required for complete release of calcium from beef liver by dry ashing, porcelain crucibles release significant amounts of calcium into the ash, which leads to erroneously high calcium values in the samples. Heated, empty porcelain crucibles do not show released calcium. Both fused silica and platinum crucibles fail to show any significant interaction with the sample. Samples dry-ashed in fused silica crucibles were compared to samples subjected to the hot trichloracetic acid-acetic acid extraction method, which gave results not significantly different if the tissue was first minced. However, calcium was incompletely extracted by the hot acid from whole segments of liver weighing about 0.2 g.