C# List＜string＞ 去重

private static void Purge(ref List<string> needToPurge)
        {

            for (int i = 0; i < needToPurge.Count - 1; i++)
            {
                string deststring = needToPurge[i];
                for (int j = i + 1; j < needToPurge.Count; j++)
                {
                    if (deststring.CompareTo(needToPurge[j]) == 0)
                    {
                        needToPurge.RemoveAt(j);
                        j--;
                        continue;
                    }
                }
            }
        }