Chemical degradation products of lignin and humic substances Part II Synthesis, structure verification and liquid chromatographic separation of chlorinated protocatechualdehydes (3,4-dihydroxy-benzaldehydes), 5-hydroxyvanillins (3,4-dihydroxy-5-methoxy-benzaldehydes) and gallaldehydes (3,4,5-trihydroxybenzaldehydes)