code: public static void clearMajorIsotopes(IMolecularFormula formula) {
          for (IIsotope iso : FluentIterable.from(formula.isotopes()).toList())
              if (isMajor(iso)) {
                  int count = formula.getIsotopeCount(iso);
                  formula.removeIsotope(iso);
                  iso.setMassNumber(null);
                  // may be immutable
                  if (iso.getMassNumber() != null) {
                      iso = formula.getBuilder().newInstance(IIsotope.class, iso.getSymbol());
                      iso.setAtomicNumber(iso.getAtomicNumber());
                  }
                  iso.setExactMass(null);
                  iso.setNaturalAbundance(null);
                  formula.addIsotope(iso, count);
              }
      }
docs: Clear the isotope information from istopes that are major (e.g.
  <sup>12</sup>C, <sup>1</sup>H, etc).
  @param formula the formula