var qry1 = datatable1.AsEnumerable().Select(a => new { MobileNo = a["ID"].ToString() });
var qry2 = datatable2.AsEnumerable().Select(b => new { MobileNo = b["ID"].ToString() });

var exceptAB = qry1.Except(qry2);

DataTable dtMisMatch = (from a in datatable1.AsEnumerable()
                           join ab in exceptAB on a["ID"].ToString() equals ab.MobileNo
                           select a).CopyToDataTable();

Kaynak: CodeProject