Firstly, I stress that the procedures to be discussed can be hazardous. Be certain you are appropriately equipped and professionally guided. I can't be there with you so I cannot be responsible for injury to yourself or others.
One volumetric (titration) method is the Devarda Method. It involves the reduction of nitrate to ammonia then a subsequent determination of ammonia (which can be a titration). It is no quick, easy method and it can be quite dangerous. Its interferences include ammonia and nitrite. The detection limit isn't great.
I don't know of any other "official" methods that use volumetric or gravimetric technology. They are inherently non-selective and you will need to be quite skeptical of results if you are not certain of the absence of interferences. They also will have relatively high detection limits.
That having been said lets say you have a solution of NaNO3 in water (after a prep step or whatever). That is, you are certain there are no other oxidizing agents present. Also, pretend that you are targeting detection limits no better than a fraction of a percent. You may be able to determine nitrate by a total oxidizing agent technique (you will have to make standards and check it out at your own risk). One procedure might go like this:
In the hood with goggles etc.
1. add NaI to an aliquot of sample (say 50 ml).
2. add (carefully!) 2 ml H3PO4 You should see evidence of I2 (yellow, red , brown) if you are on the right track
3. titrate with standardized thiosulfate to light straw color
4. add 1 ml of starch indicator (blue now)
5. titrate to clear
6. get out the CRC and go to the electrochemical series for half reactions leading to calculation