Nitrogen isotope ratio variations measured in different sources starting from small solar system bodies (in red; Busemann et al. 2006; Floss et al. 2006; Alexander et al. 2007; Bockelée-Morvan et al. 2008; Manfroid et al. 2009; Mumma & Charnley 2011; Guzmán et al. 2017) to planets (in black; Junk & Svec 1958; Hoffman et al. 1979; Fouchet et al. 2004; Niemann et al. 2005; Marty et al. 2010; Wong et al. 2013; Fletcher et al. 2014), low-mass prestellar cores (in yellow; Gerin et al. 2009; Bizzocchi et al. 2010; Lis et al. 2010; Bizzocchi et al. 2013; Hily-Blant et al. 2013), low-mass star-forming cores (in light grey; Wampfler et al. 2014) and high-mass star-forming cores (in blue; Adande & Ziurys 2012; Fontani et al. 2015). Our measurements in IRDCs are shown on the right. On the upper right corner, we show a representative error bar for our measurements of the ¹⁴N/¹⁵N ratio. Black arrows indicate the lower limits in our measurements. The ¹⁴N/¹⁵N ratio measured in HCN from core G2 is shown as zero with no lower limit indication owing to both of the column densities of H¹³CN and HC¹⁵N are only given as upper limits.