problem in encoding string

hi everyone.

here is my source code......

public static bool IsUnicode(string strMessage)
  {
   bool unicode = false;

            foreach(char chr in strMessage)
   {
    StringBuilder sb = new StringBuilder(strMessage.Length);
    //sb.Append(chr.ToString());
    Encoding enc = Encoding.GetEncoding("GB18030");
    Debug.WriteLine(sb.Append(chr.ToString()));
    if(enc.GetByteCount(chr.ToString()) == 2)
    {
     unicode = false;
     return unicode;
    }
    else
    {
     unicode = true;
    }
&nb ...