How to compare a db value to another db value in laravel php

I would like to compare 2 values of the database. Is it possible to do so with the "where" method? The "tnx_time" would be one db value and the "value(duration)" the other one. But right now I can not access the db values on the 3rd field of the "where" function.

Does anybody know how to fix that? Thanks a lot!

$trnxs =  Transaction::where('tnx_time', '<',  date("Y-m-d", strtotime( value(duration) )) )

via Chebli Mohamed