Return unique values

Hi I have a text box that has values separated by a comma. I am trying to remove the duplicate values for, example this text box will have values like:

SO-001, SO-003, SO-002, SO-001, SO-001

To return unique values like:

SO-001, SO-003, SO-002

Use this Function it

public string RemoveDuplicates(string items)
 {
  StringBuilder Result = new StringBuilder();


  String[] newArray = items.Split(',');


  for (int i = 0; i < newArray.Length; i++)
  {
   if (Result.ToString().IndexOf(newArray[i]) == -1)
   {
    Result.Append(newArray[i].ToString()).Append(",");
   }
  }
  return Result.ToString().Substring(0, Result.ToString().LastIndexOf(','));
 }

To Call this Function Like this...

textbox1.Text=RemoveDuplicates(textbox1.Text);