Sample of APEX spectra toward sources from the extended sample (see Sect. 2). The spectra for DCO⁺ J=5-4 and p-H₂CO J=5_0,5-4_0,4 were obtained with APEX-2 with a beam of 18″, the other spectra were obtained with APEX-1 and a beam of 28.7″. From left to right, the first two panels show spectra for the components of the system B1 Per6+Per10. The third panel shows spectra for the close binary L1455 Per17. The fourth panel shows spectra for the single protostellar source NGC1333 RNO 15 FIR. The spectra are averaged to 0.4 km s⁻¹ in order to increase sensitivity. All emission lines shown are found to have S/N ≥5 based on GILDAS/CLASS Gaussian fitting routines.