Determine the empirical formula of a compound containing 22.6% nitrogen and 77.4% oxygen

Empirical formula is the simplest ratio of whole numbers of components in a compound 
for 100 g of the compound 
                                          N                                  O
mass                                 22.6 g                         77.4 g
number of moles               22.6 g / 14 g/mol        77.4 g / 16 g/mol 
                                          = 1.61 mol                  = 4.84 mol
divide by the least number of moles 
                                          1.61 / 1.61  = 1.00      4.84 / 1.61 = 3.01
rounded off to nearest whole numbers 
N - 1
O - 3

therefore empirical formula - NO₃

The mass has escaped into a gas which you can not see so the law stays true.