Hey @Will_m32 and welcome to the forum!
The simplest thing you could to is to use the slice_solution method.
It expects a solution object and allows you to specify flags such as use_total_concentration (which sums up all components) and components (a list of components you want to sum up).
In your example, this could look something like this:
from CADETProcess.solution import slice_solution
solution_new = slice_solution(simulation_results.solution.column.outlet, use_total_concentration=True, components=['A', 'B', 'C'])
solution_new.plot()
Which produces the following figure:
Note that I excluded the Salt component for the new solution object.
Also note that both the Comparator, as well as the Fractionator already support slicing so you can add the components list and use_total_concentration arguments in the corresponding methods.