How to save the GUID of selected item in combobox?

hi,
its working but column name is saved but valuenot saved.plz help me.my codeing is paste  below
private void Itemmaster_Load(object sender, EventArgs e)
{
cn = new SqlConnection(System.Configuration.ConfigurationManager.AppSettings["con"]);
da1 = new SqlDataAdapter("select *from ITEMMASTER", cn);
da2 = new SqlDataAdapter("select *from ITEMCATAGARY", cn);
ds = new DataSet();
da1.Fill(ds, "ITEMMASTER");
da2.Fill(ds, "ITEMCATAGARY");
cmd = new SqlCommand();
comboBox1.DataSource = ds.Tables["ITEMCATAGARY"];
comboBox1.DisplayMember = "Itemname";
comboBox1.ValueMember = "guid";
comboBox1.EndUpdate();
}
 
 
private void Add_btn_Click(object sender, EventArgs e)
{
try
{
DataRow dr = ds.Tables["ITEMMASTER"].NewRow();
dr[1] = textBox1.Text;
dr[2] = textBox2.Text;
dr[3] = textBox3.Text;
dr[4] = comboBox1.ValueMember.ToString();
dr[5] = textBox5.Text;
dr[6] = textBox6.Text;
dr[7] = dateTimePicker1.Text;
dr[8] = textBox8.Text;
dr[9] = textBox9.Text;
dr[10] = textBox10.Text;
dr[11] = textBox11.Text;
dr[12] = textBox12.Text;
dr[13] = textBox13.Text;
dr[14] = textBox14.Text;
ds.Tables["ITEMMASTER"].Rows.Add(dr);
cb = new SqlCommandBuilder(da1);
da1.Update(ds, "ITEMMASTER");
MessageBox.Show("Data Saved Successfully");
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
foreach (Control item in Controls)
{
if (item is TextBox)
{
item.Text = "";
}
}

}
PLZ HELP ME

well what you need todo is the following
select id,value from tbl
the ID is the guid and the value is the display
than on the combo bind it to the sql return datatable
 this.cbPositions.DataSource =dt;
this.cbPositions.DisplayMember = "Name";
 this.cbPositions.ValueMember="ID";

and on selected take cbPositions.selectedValue