As the previous answerer said, an acid base titration wouldn't be suitable for NaNO_3 if water is the solvent, as NO_3^- is too weak a base to change the pH to make a titration suitable. The same goes for Na^+ but being too weak an acid.
NO_3^- has no insoluble salts, or at least no common insoluble salts, so we can't do a precipitation titration either. Na^+ has this same trouble.
NO_3^- isn't a good coordinating agent so a complexation titration isn't viable either. There is a complexating agent for Na^+ and other alkali metals, but it's rarely used and expensive so it isn't worth considering.
Na^+ won't reduce to Na^0 easily, and if it does it'll react with water violently so it isn't a good idea to do it either.
NO_3^- does have a redox reaction though,
NO_3^(-) + 3H^+ +2e^(-) harr HNO_2 + H_2O E_(red)^0 = 0,94
Which could theoretically be coupled with I^- to produce I_3^- which can then be titrated with S_2O_3^-2.
3I^(-) harr I_3^(-) + 2e^(-) E_(o.x)^0 = -0,536
That being said, I'm not sure if the DeltaE would be big enough outside of standard conditions.
E^0 values copied from Skoog's fundamentals of Analytic Chemistry
