No, you did not mention the ZEND.
However, this insert as you have typed it contains the variable names instead of variable values. Is this the php code or the result from the php echo command?
I am not 100% sure you need the table and field names surrounded by ' ', but, still if it works, maybe it is ok.
Why don't you try this code. It works fine for me in multiple pages, so I have it verified numerous times.
$sql = 'INSERT INTO article_fields VALUES (NULL, \''.$new_text.'\', \''.$field_type.'\')';
I think that this code will be ok also for the zend framework.
" Of all the things I've lost,
I miss my mind the most...."
Mark Twain