calculate the parts per million of 128 mg of sodium ions in 550 ml of a water sample

Parts per million is given by : $$ \frac{mass\:of\:Na}{mass\:of\:H_2O}\times10^6 $$ Mass of H2O = 550 g Mass of Na = 128 mg = 0.128 g $$ \frac{128\times10^{-3}}{550}\times10^6\xrightarrow{}\frac{128000}{550} $$ $$ =232.72 ppm $$