How to remove space around a character?

A fast version could be:

function RemoveSpacesAroundDelimiter(const aString: string; aDelimiter: char = ','): string;
var S, D, D2: PChar;
begin
  SetLength(result,length(aString));
  if aString<>'' then
  begin
    S := pointer(aString);
    D := pointer(result);
    while S^<>#0 do
    begin
      if S^=' ' then
      begin
        D2 := D;
        repeat
          inc(S);
          D^ := ' ';
          inc(D);
        until S^<>' ';
        if S^=#0 then
          break;
        if S^=aDelimiter then
          D := D2; // trim spaces before comma
      end;
      D^ := S^;
      if (S[0]=aDelimiter) and (S[1]=' ') then
        repeat inc(S) until S^<>' ' else // trim spaces after comma
        inc(S);
      inc(D);
    end;
    SetLength(result,D-pointer(result));
  end;
end;

Some test code:

  assert(RemoveSpacesAroundDelimiter('one two,three')='one two,three');
  assert(RemoveSpacesAroundDelimiter('one two , three')='one two,three');
  assert(RemoveSpacesAroundDelimiter('one,two,three')='one,two,three');
  assert(RemoveSpacesAroundDelimiter('one   ,   two,  three')='one,two,three');

Sounds like a task for TStringList.

function UltraTrim(Value: string): string;
var
  sl: TStringList;
  i: Integer;
begin
  sl := TStringList.Create;
  try
    // Prevent the stringlist from using spaces as delimiters too.
    sl.StrictDelimiter := True;

    // Set the comma separated text.
    sl.CommaText := Value;

    // Trim each item.
    for i := 0 to sl.Count -1 do
      sl[i] := Trim(sl[i]);

    // Concat back to comma separated string.
    Result := sl.CommaText;
  finally
    sl.Free;
  end;

end;