I want to fetch alphanumeric max/min value from sqlserver

Protected Sub btnFirst_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles btnFirst.Click
      Dim i As Long = 0

      Dim str1 As String = "SELECT Min(IT_CODE_ACT) FROM PS_EXT_MAST "

      conn.Open()
      Dim cmd1 As SqlCommand = New SqlCommand(str1, conn)
      Dim dr As SqlDataReader = cmd1.ExecuteReader()

      dr.Read()
      If dr.HasRows Then
          txtItemCode.Text = dr(0).ToString()
          i = Convert.ToInt32(txtItemCode.Text)
      End If
      conn.Close()

      Dim str2 As String = "select IT_DESC from PS_EXT_MAST where IT_CODE_ACT= " + i
      conn.Open()
      Dim cmd2 As SqlCommand = New SqlCommand(str2, conn)
      Dim dr2 As SqlDataReader = cmd2.ExecuteReader()
      dr2.Read()

      If dr2.HasRows Then
          txtItemDesc.Text = dr2(0).ToString()

      End If
      conn.Close()

      Response.Write("<Script>alert(' First record found....')</Script>")
  End Sub

  Protected Sub btnLast_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles btnLast.Click
      Dim i As Long = 0

      Dim str1 As String = "SELECT Max(IT_CODE_ACT) FROM PS_EXT_MAST"
      conn.Open()
      Dim cmd1 As SqlCommand = New SqlCommand(str1, conn)
      Dim dr As SqlDataReader = cmd1.ExecuteReader()

      dr.Read()
      If dr.HasRows Then
          txtItemCode.Text = dr(0).ToString()
          i = Convert.ToInt32(txtItemCode.Text)
      End If
      conn.Close()

      Dim str2 As String = "select IT_DESC from PS_EXT_MAST where IT_CODE_ACT=" + i
      conn.Open()
      Dim cmd2 As SqlCommand = New SqlCommand(str2, conn)
      Dim dr2 As SqlDataReader = cmd2.ExecuteReader()
      dr2.Read()
      If dr2.HasRows Then
          txtItemDesc.Text = dr2(0).ToString()
      End If
      conn.Close()

      Response.Write("<Script>alert(' Last record found....')</Script>")
  End Sub