code: public static boolean isWithinPpm(double mz1, double mz2, double ppm) {
      return Math.abs(amu2ppm(mz1, mz1 - mz2)) <= ppm;
    }
docs: Check if the 2nd m/z value is within some PPM distance from the 1st one. PPM will be calculated
  based on the 1st m/z value.
  
  @param mz1 PPM tolerance will be calculated relative to this value
  @param mz2 the value to check for being within some PPM range