The only metal in the buffer solution, sodium, also gave five CheckMyMetal outliers, including even more extreme outliers from typical N-Na bond lengths (2.46 ± 0.02 Å, Z = -29 and -40) , and a much worse fit to the density than magnesium . Indeed, no metal forms coordination bonds to N shorter than 1.76 Å . It is thus extremely implausible that the missing atom is a metal.