What is your problem. 100 characters / second is way less than you can get with 19200 baud.

So what is your problem? That the analog data requires very many characters? Remember that the size of the data to send is greatly affected by how you send it. If running 19200 baud you have about 20 characters/measurement available and even if you add a bit of safety margin and say that you may only consume 15 characters/value, that means you can send 14 decimal digits and a carriage return - 14 decimal digits is 0 to 99,999,999,999,999 which means that you may use an ADC with a huge number of bits of resolution without still managing to produce too much data.