CFRelease call manually ! SOS!

Hey,

I have problem getting finder comment value on file .... Sometimes application user cashed comment... (shows old one) . Here is my code :

            var fileURL = NSUrl.FromFilename (imgPath);
            var mMDItemRef = MDItemCreateWithURL (IntPtr.Zero, fileURL.Handle);
            var mCFTypeRef = MDItemCopyAttribute (mMDItemRef, new CFString ("kMDItemFinderComment").Handle);
            var finderComment = NSString.FromHandle (mCFTypeRef);
            fileURL = null;

            return finderComment;

While searching I found the example:

StringRef comment = MDItemCopyAttribute(item,kMDItemFinderComment);
if (comment)
{
[metadata setObject:(NSString*)comment forKey:@comment];
CFRelease(comment);
}

what I messing is to call CFRelease ... but have no idea how to use it in xamarin....

Any help?