def METHOD_NAME(s):
    """
    Check if text is plausibly an isotope ratio.
    Parameters
    -----------
    s : :class:`str`
        String to validate.
    Returns
    --------
    :class:`bool`
    Todo
    -----
        * Validate the isotope masses vs natural isotopes
    """
    if s not in _common_oxides:
        isotopes = get_isotopes(s)
        return len(isotopes) == 2
    else:
        return False