String won't url encode in iOS

For future reference, this is what I found to work (i.e. encode everything properly)

+ (NSString*)encodeURL:(NSString *)string
{
    NSString *newString = (__bridge NSString *)CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault, (__bridge CFStringRef)string, NULL, CFSTR(":/?#[]@!$ &'()*+,;=\"<>%{}|\\^~`"), CFStringConvertNSStringEncodingToEncoding(NSUTF8StringEncoding));

    if (newString) 
    {
        return newString;
    }

    return @"";
}

& is a reserved character http://www.blooberry.com/indexdot/html/topics/urlencoding.htm