how can i accept xml files on my webservice using php (codeigniter)?

I just did a web service with the proper methods and everything.. they work fine if you send the parameters with your php file, I am using NuSoap, so, basically I do something like this

$client = new soapclient(WSURL);
$client->function(parameter1, paramenter2,...)

It works fine, but I am wondering, what if they have ' or " at the paramenters are sending? plus, i might need to accept xml files that were already done, is it possible? how can i do it?

Thanks.