set one item in multiple querystrings

var qs = HttpUtility.ParseQueryString(Request.QueryString.ToString());
qs.Set("item", newItemValue);
Console.WriteLine(qs.ToString());

var qs = HttpUtility.ParseQueryString(Request.QueryString.ToString());
            qs.Set("cityId", city.CityId.ToString());
            string url = Request.FilePath;
            hpl.NavigateUrl = url + "?" + qs.ToString();