Select unselect checkboxes using jquery

I have a list of checkboxes in my kendo grid.Select all option is also there. Problem is When i click select all then all the checkboxes selected and then unselect some checkboxes and going to save then it shows me all the checkboxes.(un checked checkboxes also shown )

My Code

    $('#itemGrid').on('change', '.usedchk', function () {


    var checked = $(this).is(':checked');
    var grid = $('#itemGrid').data().kendoGrid;
    var dataItem = grid.dataItem($(this).closest('tr'));
    var selected = $('#selected').val();
    var id = dataItem.itemId;

    if ($('#selected').val().indexOf(id) == -1) {
        if ($('#selected').val() == '') {
            $('#selected').val(id);
        } else {
            $('#selected').val(selected + "," + id );
        }
    }
});