Dear Raneesha Navaretam, please have a look at the following similar RG thread. My Regards

https://www.researchgate.net/post/What_nitric_acid_concentration_should_be_used_for_digestion_on_SUS_extractions_for_ICP-MS_analysis

That little bias in nitric acid concentration will not have an effect on organic matter digestion.

Regards.

Yeah, you could use this concentration of nitric, and it would have no effect on the digestion of organic matter.

Thank you so much Mr. Mahmoud Mohamed Abdelfarrag and Dr Antonio De Vega

Absolutely Yes. You can use 69% concentrated Nitric Acid as well for acid digestion. Nitric acid, analytical grade, does not play major role in the acid digestion it only has very less impurities (like As, Cd, Hg, Pb etc.) so your results would be more accurate if you use analytical grade acid.

Thank you so much for your answer Jitendra Pratap . Much appreciated. However, why do most articles specifically digesting rice samples for heavy metals use 65% nitric acid instead of higher purity nitric acid? For example, one study used 69% nitric acid but in the case of digesting fish samples for heavy metals.