An Opamp Comparator Design I made
This is unlikely to work as you intend with most op-amps. If the input signal is, for example, -4 V and the non-inverting input is held at -8 V then it will be 4 V below the negative supply pin. 

Check the datatsheet for the device you used in your simulation (and forgot to link in your question) to see how far below the negative supply rail you are allowed to go.