  The existence of an anti-correlation between the Equivalent Width (EW) of the
neutral narrow core of the iron Kalpha emission line and the 2-10 keV
luminosity (the so-called `X-ray Baldwin' or `Iwasawa-Taniguchi' effect) has
been debated in the last years. We aim at testing this claim on the largest
catalogue of radio quiet AGN high-quality X-ray spectra ever published. The
final sample comprises 157 objects. We search for a relation of the iron line
EW not only with the X-ray luminosity, but also with the Black Hole mass, the
Eddington ratio and the cosmological distance. The data presented here were
analyzed homogeneously, all spectra are from the same instrument and with high
Signal-to-Noise Ratio. A linear censored fit on the EW versus 2-10 keV
luminosity is highly significant and yields $\log(EW_{Fe}) = (1.73\pm0.03) +
(-0.17\pm0.03) \log(L_{X,44})$, where $EW_{Fe}$ is the EW of the neutral iron
Kalpha line in eV and $L_{x,44}$ is the 2-10 keV X-ray luminosity in units of
$10^{44}$ erg s$^{-1}$. The anti-correlation with the Eddington ratio is also
very significant, while no dependence of the iron EW on the BH mass is
apparent.
