$5.40\pm0.06$ & 7\
NGC 6572 & $11.01\pm0.02$ & $8.53\pm0.02$ & $7.41^{+0.20}_{-0.10}$ & $8.56^{+0.06}_{-0.04}$ & – & $4.53\pm0.08$ & 7\
NGC 6620 & $11.07\pm0.02$ & $10.33\pm0.02$ & $8.20\pm0.06$ & $8.69\pm0.04$ & 5.31 & $5.05^{+0.12}_{-0.16}$ & 1\
NGC 6720 & $10.96\pm0.02$ & $10.25\pm0.02$ & $8.24^{+0.06}_{-0.05}$ & $8.46\pm0.05$ & 4.26 & $4.77\pm0.06$ & 4\
NGC 6741 & $10.89\pm0.02$ & $10.49\pm0.02$ & $8.10^{+0.19}_{-0.11}$ & $8.39\pm0.05$ & 5.58 & $5.68^{+0.07}_{-0.05}$& 7\
NGC 6803 & $11.04\pm0.02$ & $9.56\pm0.02$ & $7.38\pm0.08$ & $8.63\pm0.05$ & – & $4.87^{+0.06}_{-0.05}$ & 3\
NGC 6818 & $10.73\pm0.02$ & $10.72\pm0.02$ & $7.36^{+0.07}_{-0.06}$ & $8.35\pm0.04$ & – & $4.68\pm0.06$ & 1\
NGC 6826 & $11.00\pm0.02$ & $7.34^{+0.11}_{-0.15}$ &$6.99\pm0.09$ & $8.50\pm0.05$ & – & $4.69\pm0.08$ & 3\
NGC 6884 & $10.87\pm0.02$ & $10.19\pm0.02$ & $7.16^{+0.09}_{-0.07}$ & $8.53\pm0.05$ & 4.04 & $4.72\pm0.06$ & 6\
NGC 7026 & $11.04\pm0.02$ & $10.11\pm0.02$ & $7.76^{+0.06}_{-0.05}$ & $8.60\pm0.05$ & – & $<4.67$ & 1?\
NGC 7662 & $10.82\pm0.02$ & $10.58\pm0.02$ & $6.28\pm0.06$ & $8.23^{+0.06}_{-0.05}$ & – & $4.40\pm0.06$ & 4\
Vy 2-1 & $11.11\pm0.02$ & $8.71^{+0.08}_{-0.10}$ & $7.90^{+0.23}_{-0.06}$ & $8.72\pm0.04$ & – & $4.86^{+0.16}_{-0.07}$ & 2

Total abundances with an ICF {#sec:tot_ab}
----------------------------

The absence of lines in seven PNe of the sample indicates that their He$^{++}$ abundances are 