Testing for nitrate ions with NaNO3 in Devarda's test
Quoting from Svelha G., Vogel's Qualitative Inorganic Analysis, 


  A solution of nitrate ion is boiled with zinc dust/aluminium powder
  and sodium hydroxide solution to get positive result. Excellent result
  is obtained by the use of Devarda's alloy (45% Al, 5% Zn, 50% Cu) but
  the ammonium ions must be removed by boiling the solution with sodium
  hydroxide solution or almost evaporating it to dryness before addition
  to metal.
  
  The overall reaction is: 
  
  $$\ce{3NO3- + 8Al + 5OH- + 18H2O -&gt;3NH3 ^ + 8[Al(OH)4]-}$$