e}$]{} as the weighted mean of the values implied by the available diagnostic ratios, here the final [$n_{\rm e}$]{}  is the median value of the density distribution obtained from averaging the [$n_{\rm e}$]{}  values calculated in each run of the Montecarlo simulation. One of the objects with significant differences is NGC 3587, where @DelgadoInglada_09 used the \[\] density diagnostic and found [$n_{\rm e}$]{} $<100$ [$\rm{cm}^{-3}$]{}, whereas here we also use the \[\] diagnostic and find [$n_{\rm e}$]{}$= 2400$ [$\rm{cm}^{-3}$]{}. This change in [$n_{\rm e}$]{} implies a change in [$T_{\rm e}$]{}[\[\]]{} from 9800 K to 10900 K. In general, [$T_{\rm e}$]{}differences are smaller, around 100 K in most of the objects. The new values derived for the physical conditions imply oxygen abundances that are within $\pm$0.15 dex of the old values. These differences illustrate the abundance uncertainties introduced by the approach chosen to perform the calculations.

Iron depletion factors {#sec:depletion}
======================

Ionic abundances {#sec:ionic_ab}
----------------

The total iron abundances of the sample PNe are calculated from the Fe$^{++}$ abundance (and Fe$^{+}$ in some cases) along with ionization correction factors (ICFs) based on the ionic and total oxygen abundances. On the other hand, the ICF we use for oxygen is based on 