this will be helpful, try this
for (int i = 0; i < GridView1.Rows.Count; i++)
{
CheckBox chkDelete = (CheckBox)GridView1.Rows[i].FindControl("chkSelect");
if (chkDelete != null)
{
if (chkDelete.Checked)
{
Label myLabel = (Label)GridView1.Rows[i].FindControl("TEXT_CONTROL_ID");
idCollection.Add(myLabel.Text);
}
}
}