Use of String Builder in C#

#region Submit-Record-using-string-builder
        if (con.State == ConnectionState.Closed)
            con.Open();
        SqlTransaction trans;
        trans = con.BeginTransaction();
        try
        {
            
            StringBuilder sb = new StringBuilder();
            foreach (GridItem item in RadGridItems.MasterTableView.Items)
            {
                sb.Append("Update RequisitionSlipDetail Set IsApproved='");
                sb.Append((item.FindControl("chkapprovequantity") as CheckBox).Checked);
                sb.Append("', ApprovedQuantity=");
                sb.Append((item.FindControl("txtapprovedquantity") as TextBox).Text);
                sb.Append(" where SerialNo=");
                sb.Append((item.FindControl("SerialNoLabel") as Label).Text);
                sb.Append(" and ItemCode='");
                sb.Append((item.FindControl("ItemCodeLabel") as Label).Text);
                sb.Append("'"); 
            }
            cmd.Connection = con;
            cmd.CommandText = sb.ToString();
            cmd.CommandType = CommandType.Text;
            cmd.Transaction = trans;
            cmd.ExecuteNonQuery();
            trans.Commit();
            cmd.Dispose();
            con.Close();
        }
        catch(Exception ex)
        {
            trans.Rollback();
            lblmsg.Text = ex.Message.ToString();
            lblmsg.Visible = true;
            
        }
        finally
        {
            trans.Dispose();
            con.Close();
        }
        #endregion