add a username to check in the follow function.

I would like to modifiy the function below and check for the username in the group of members.

            string fullname = System.Security.Principal.WindowsIdentity.GetCurrent().Name.ToString();
            string[] parts = fullname.Split('\\');
            string sDomain = parts[0];
            string sUser = parts[1];
            string sGroup = "gl ca corporate data";
            StringCollection groupMembers = this.GetGroupMembers(sDomain, sGroup, sUser);
 



I have a function that gets group members

 public StringCollection GetGroupMembers(string strDomain, string strGroup,  ?)
        {
            StringCollection groupMemebers = new StringCollection();
            try
            {
                DirectoryEntry ent = new DirectoryEntry(_path);
                DirectorySearcher srch = new DirectorySearcher("(CN=" + strGroup + ")");
                SearchResultCollection coll = srch.FindAll();
                foreach (SearchResult rs in coll)
                {
                    ResultPropertyCollection resultPropColl = rs.Properties;
                    foreach (Object memberColl in resultPropColl["member"])
                    {
                        DirectoryEntry gpMemberEntry = new DirectoryEntry("LDAP://" + memberColl);
                        System.DirectoryServices.PropertyCollection userProps = gpMemberEntry.Properties;
                        object obVal = userProps["sAMAccountName"].Value;
                        if (null != obVal)
                        {
                            groupMemebers.Add(obVal.ToString());
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Trace.Write(ex.Message);
            }
            return groupMemebers;
        }