$re = '/^(?:"[^"]*",){1}"([^"]*)"/mix';
$str = '"01","35005","AL","ADAMSVILLE",86.959727,33.588437,10616,0.002627
"05","72001","AR","ADONA",92.903325,35.046956,494,0.00021
"06","90804","CA","SIGNAL HILL",118.155187,33.782993,36092,0.001213';
$subst = "$1chat/$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php