If you're receiving the values as a comma-separated list, then you should format them in the back-end. In other words, you need to format the values before the concatenation.
Luis C.
General Disclaimer:
Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?
How to post data/code on a forum to get the best help: Option 1 / Option 2