Hi Dave,
You need to pass the id as querystring in order to get the value in article page. Check with the below way.
<a href="<%= item["Url"]+ "/"+"Article.aspx?id="+item["Url"]%>">
Here you need to pass the id as query string to get the id. I am passing url as id. So you need to change that as per your id field.
To get the value in article page using the below code.
if (Request.QueryString["id"] != null)
{
int id = Convert.ToInt32(Request.QueryString["id"]);
}