def add_conc(self,column_name,x,y,new_name='default'):
        """
        calculates the concentration values of the given column and adds them as
        a new column to the DataFrame.

        Parameters
        ----------
        column_name : str
            column with values
        x : int
            ...
        y : int
            ...
        new_name : str
            name of the new column, default to 'column_name + mg/L'
        """
        if new_name == 'default':
            new_name = column_name + ' ' + 'mg/L'

        self.data[new_name] = self.data[column_name].values*x*y