(a): MIREX derived mass surface density map of IRDC G28.37+00.07 from Kainulainen & Tan (2013) (scalebar is in g cm⁻²). The 10 regions selected for our astrochemical study are marked with circles, labelled 1 to 10. Regions 1 to 6 (red) are known to harbour some star formation activity, while regions 7-10 have been specifically selected to avoid known protostellar sources. (b): sub-mm emission derived mass surface density map of the IRDC from Lim et al. (2016) using the Galactic Gaussian method of foreground-background subtraction (scalebar is in g cm⁻²). We note that it is of significantly lower angular resolution than the MIREX map (see text). The analysed positions are marked as in (a).