code: private HashMap<String, Integer> getDNP_500() {
          HashMap<String, Integer> map = new HashMap<String, Integer>();
  
          map.put("C", 29);
          map.put("H", 72);
          map.put("N", 10);
          map.put("O", 18);
          map.put("P", 4);
          map.put("S", 7);
          map.put("F", 15);
          map.put("Cl", 8);
          map.put("Br", 5);
  
          return map;
      }
docs: Get the map linking the symbol of the element and number maximum of occurrence.
  For the analysis with the DNP database and mass lower than 500 Da.
  
  @return The HashMap of the symbol linked with the maximum occurrence