php php codeigniter ต้องการส่งค่า Select (List/Menu) ตาม site_url("we_po/select_im/".$?????) ยังไง

function small_window(myurl) {
	var newWindow;
	var props ='scrollBars=yes,resizable=yes,toolbar=no,menubar=no,location=no,directories=no,'+
	'width=650,height=400';
	newWindow = window.open(myurl, "Add_from_Src_to_Dest", props);
}

<table width="1024" border="0" cellpadding="1" cellspacing="1" bgcolor="#CCCCCC">
      <tr bgcolor="#FFFFFF">
        <td width="225"><span class="txt_master_n">
          <select name="txtType2" id="txtType2">
            <option value="Care Instructions">Care Instructions</option>
            <? include 'select_type.txt';?>
          </select>
        </span></td>
        <td width="789"><input name="txtData2" type="text" id="txtData2" size="118">          <input name="button" type="button" id="button" value=" ... " onClick="javascript:small_window('<?php echo site_url("we_po/select_im/");?>');"></td>
        </tr>
    </table>