By wet digestion-Transfer 10.00 g test portion to 800 ml Kjeldahl flask, previously rinsed with dilute acid, then with H2O ;add 20ml H2O and mix, pipet 5 ml H2SO4 into flask and mix : add 25 ml HNO3 and mix well. After 2-3 min,heat flask very gently at brief intervals (to avoid foaming out of flask) until heavy evolution of NO2 fumes ceases. Continue to heat gently until SO3 fumes evolve and colorless or very pale yellow liquid is obtained (60-65 ml HNO3 total in ca 2 h). Cool, add 50 ml H2O and 1 glass bead, and heat to SO3 fumes; cool, add 25 ml H2O, and filter quantitatively through 11 cm paper into 100 ml volumetric flask;cool.and dilute to volume.
Pipet 10 ml into 25 ml volumetric flask, add 1 ml H2NOH•HCl solution, rotate flask, and let stand 2-3 min. add 9.5 ml 2 M NaC2H3O3 solution, A(g), and 1 ml o-phenanthroline solution. Dilute to volume, and mix. Let stand ≥ 5 min and determine A in spectrophotometer or photometer at ca 510 nm.
By wet digestion-Transfer 10.00 g test portion to 800 ml Kjeldahl flask, previously rinsed with dilute acid, then with H2O ;add 20ml H2O and mix, pipet 5 ml H2SO4 into flask and mix : add 25 ml HNO3 and mix well. After 2-3 min,heat flask very gently at brief intervals (to avoid foaming out of flask) until heavy evolution of NO2 fumes ceases. Continue to heat gently until SO3 fumes evolve and colorless or very pale yellow liquid is obtained (60-65 ml HNO3 total in ca 2 h). Cool, add 50 ml H2O and 1 glass bead, and heat to SO3 fumes; cool, add 25 ml H2O, and filter quantitatively through 11 cm paper into 100 ml volumetric flask;cool.and dilute to volume. Pipet 10 ml into 25 ml volumetric flask, add 1 ml H2NOH•HCl solution, rotate flask, and let stand 2-3 min. add 9.5 ml 2 M NaC2H3O3 solution, A(g), and 1 ml o-phenanthroline solution. Dilute to volume, and mix. Let stand ≥ 5 min and determine A in spectrophotometer or photometer at ca 510 nm.
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