How to execute saved search using custom field as filter

@operator

Hello all,
I cannot seem to figure out how to run a saved search using a custom field as a filter in SuiteTalk using C#.  I can filter by other fields (i.e. itemID) but not a custom field.

The following works for a standard field

                        ItemSearchAdvanced itmSearchAdv = new ItemSearchAdvanced
                        {
                            savedSearchScriptId = "customsearch_pe_itemprefbin",

                            //criteria added
                            criteria = new ItemSearch
                            {
                                basic = new ItemSearchBasic
                                {
                                    itemId = new SearchStringField
                                    {
                                        @operator = SearchStringFieldOperator.@is,
                                        operatorSpecified = true,
                                        searchValue = txtItem.Text.Trim()
                                    }
                                }
                            }
                        };

                        SearchResult searchResult = _service.search(itmSearchAdv);


But nothing I have tried lets me search on our custom eancode field.  I have seen one PHP example but no c# and trying to convert what they did in PHP I was unable to get it to work.