Accessing user name of a NTID using LDAP

public static string GetFirstName(string NTID)
{
char[] seperator ={','};
char[] sep1 = {'('};
string [] st = CheckLDAPUser(NTID).Split(seperator);
string[] sp = st[1].Split(sep1);
return sp[0].ToString();
}

private static string CheckLDAPUser(string ldapUserId)
{
System.DirectoryServices.DirectoryEntry directoryEntry = new System.DirectoryServices.DirectoryEntry("LDAP://CompanyNameURL");
System.DirectoryServices.DirectorySearcher directorySearcher = new System.DirectoryServices.DirectorySearcher(directoryEntry);
directorySearcher.Filter = "(SAMAccountName=" + ldapUserId + ")";
System.DirectoryServices.SearchResult sResultSet = directorySearcher.FindOne();
string fullName = "";
if (sResultSet != null)
{
if (sResultSet.Properties.Contains("displayName"))
{
fullName = sResultSet.Properties["displayName"][0].ToString();
}

return fullName;
}
return "Anonymous";
}