If I understand your question correctly:

The atomic weight of nitrogen is 14, and the molecular weight of nitrate is 62.

So  As-nitrate = X% N / 14 * 62.

If you are being precise, you should look up the precise atomic weights.

If your sample was pure NaNO3, with no waters of hydration, it should be c. 73% nitrate by weight.

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In the U.S., P and K in fertilizer is expressed as P2O5 and K2O.  If my explanation isn't clear, it might be helpful to look up how to express fertilizer P as P and as P2O5.

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Another example, in the U.S. there is a benchmark for nitrate in drinking water of 10 mg/L nitrate-N or 44 mg/L nitrate, which are equivalent.

Thanks for your immediate response. Could you tell me any antifoam agent used while distilling the meat with Devarda  alloy. Usually, sodium nitrite/nitrate is added as an antimicrobial agent in meat

That I know nothing about.