DataGrid. How to keep the right keyfield value when Sort the DataGrid?

[Eugene]

Hi everybody!

Got the logical error (wrong row (SSN) selected on
SelectedIndexChange event) when made a sort by non-key field in
Datagrid.

Used this Sub to keep the keyfield ("SSN"):

Private Sub dgrMain_SelectedIndexChanged(ByVal sender As
System.Object,ByVal e As System.EventArgs) Handles
dgrMain.SelectedIndexChanged
Session("SSN") =
dgrMain.Items(dgrMain.SelectedIndex).Cells(1).Text
Response.Redirect("Default.aspx")
End Sub

Did sorting in a standart way. Everything works fine when the Grid is
sorted by SSN (what is cells(1)). But when you sort by any other field
it still choose the row like sorted by SSN.
Thanks for the help.
Eugene