How to use date_make_date() in drupal 7?
The alternative to the date_make_date function in D7 is the DateObject, which extends the PHP DateTime class.

To make your code work properly, you'd do something like this (untested): 

$local_date = new DateTime($dateTxt, $timezone); //$timezone can be string or object
$iso_date_string = $local_date-&gt;toIso(); //returns the ISO string for the date
$utc_date = clone $local_date; //don't want pass by reference
$utc_date-&gt;setTimezone(new DateTimeZone('UTC')); //set the new timezone to return
$utc_date_iso = $utc_date-&gt;toIso(); //returns $local_date converted to UTC as an ISO string.


I'm not totally sure what you want to do, but this, hopefully, will get you on the right path.