2.5. Determination of the metal ion concentration of MR, VOR and CCWP
Each sample (0.50 g) was charred in silica dishes in a fume hood until no more smoke evolved. The samples were transferred to a muffle furnace and ashed at 550 °C for 5–6 h until nearly a whitish ash was obtained. After cooling the samples in a desiccator, 3 ml of 5 M nitric acid was added to each, evaporated to dryness and ashed at 400 °C for 5 min. The ash was moistened with little water followed by 6 M HCl (10 ml) and the contents evaporated to dryness on a steam bath under a fume hood. The dishes were covered with watch glasses throughout the procedure. The contents were heated at 100 °C in an oven followed by addition of conc. HCl (2 ml) and boiled in a steam bath for 2 min. The contents were dissolved in distilled water and quantitatively transferred to a 50 ml volumetric flask through a fluted filter paper (Whatman 42). The volume was made up to the mark. Blank sample was also prepared in a similar manner without the sample. The metal ion concentration of the fibre was determined by Atomic absorption spectrophotometer (GBC 904AA, Australia) with relevant hollow cathode lamps.