Thermocouple Simulation Test Circuit and Voltage Comparator Circuit
The approach you are proposing might look okay in a simulation.  But it's very unlikely to work in real life (i.e. it will not work).  8.3mV is a weak signal.  You can easily have more than 8.3mV of noise in your system.  The noise will be tripping your comparator, and you will be having false detections all the time.

In real life practice, a thermocouple signal (tens of μV/°C) is amplified before something useful can be done with it.  The amplification is usually done with an instrumentation amplifier.  There are also specialized thermocouple front end ICs.

You should also look into Cold Junction Compensation of thermocouples.  It's also sometimes called Ice Point Compensation.

There many application notes on thermocouple signal conditioning.  Just search for these terms.