using System;

using System.Web;

public class Program

{

    public static void Main()

    {

        string input="/article/dmf290484743?utm_source=hallo&deviceid=jfgghfhg";

        string prefix="https://testbrooklynapi.nieuwsblad.be";

        Console.WriteLine(RemoveQueryStringByKey(input,prefix));

    }

        public static Uri RemoveQueryStringByKey(string url, string prefix)

        {

            var uri = new Uri(prefix+url);

​

            var newQueryString = HttpUtility.ParseQueryString(uri.Query);

            newQueryString.Remove("deviceid");

            var uriBuilder = new UriBuilder(uri);

            uriBuilder.Query=newQueryString.ToString();

            return uriBuilder.Uri;

        }

}