How do i use delimiter?

Is there any idea how do i use delimiter in this case so as to extract ", " out ? Much help will be appreciated!

selectedProducts = selectedProducts + "," + cb.Value;

Product.Add(selectedProducts);

LblText.Text = selectedProducts;
string url = "CompareProducts.aspx?prodId=" + selectedProducts.Substring(selectedProducts.LastIndexOf(',') + 1);

Response.Redirect(url);