How can I get a value from a table into an XML without bringing in the column title?

I'm using the following function to bring a PaymentAmount from my database into an XML.

    function GetPaymentTotal($orderID) {

      Global $cnx;
      $ptotal = null;

      $sql    = "SELECT value FROM orders_total WHERE class='ot_total' AND orders_id = '" . $orderID . "'";
      $result = mysql_query($sql, $cnx) or die('Couldn\'t get order ot_shipping class from ' . SHOPPING_CART . ' orders_total table: ' . mysql_error());
      if (mysql_num_rows($result) > 0)
      {
          $ptotal = mysql_fetch_assoc($result);
      }  

      return $ptotal;

    }

Using this to output:

$a_order['PaymentAmount']   = GetPaymentTotal($order->OrderNumber);

It's working, but for some reason it's bringing in the 'value' tags either side of my value... which I don't want. Here's how it looks at the minute:

<PaymentAmount>
   <value>74.8501</value>
</PaymentAmount>

Here's how I want it to look.

<PaymentAmount>74.8501</PaymentAmount>

Any help would be greatly appreciated.