Evaluation of recycle and reuse of nitric acid from sample digests by sub-boiling distillation

An analytical procedure was developed for recovering HNO3 from sample digests generated after microwave-assisted digestion procedures. Rice and bovine muscle digests were mixed with technical grade HNO3 in different proportions and submitted to distillation using a sub-boiling apparatus. Arsenic, Ca, Cu, Fe, Mg, Mn, Na, P, and Zn were determined before and after distillation of solutions, revealing that the procedure was efficient for removal of most contaminants. It was observed that the percentage of contaminant removal ranged from 98.1 to 99.8% for all evaluated procedures. Two certified reference materials, NIST 8414 (Bovine Muscle) and NIST 1570a (Spinach Leaves), were digested using recovered acid from rice digests by sub-boiling distillation and all analyte recoveries ranged from 73 to 106%. Digests obtained from NIST 8414 were also submitted to the same sub-boiling distillation procedure and As, Al, Ca, Cd, Co, Cu, Fe, Mg, Mn, Na, P, Pb, Se, Sr, V, and Zn were determined. Sub-boiling distillation of sample digests is a promising procedure for adopting green chemistry principles, such as minimizing the quantity of residues generated and recycling of reagents.