of these data (medium-$Z$ elements), currently observed in the X-ray spectrum of active galactic nuclei (AGNs, e.g., 3783 [@kaspi2002a; @ramirez2005a; @ramirez2011a], [@ramirez2008b], [@ramirez2008a], Ark 564 [@ramirez2013a]), in the form of K-absorption lines of H- and He-like Ne,Mg,Si,S, possibly Ar and Ca, and also from lower and medium ionization stages of Si and S (e.g., for MCG-6-30-15 and IRAS 13349+2438) ([@holczer2007a]), with the aim of improving the atomic database of the modelling code.

We report on the accuracy of the statistical method, [xline-id]{} which allows us to extract time averaged gas density $n_H$ of interacting material surrounding UV+X-rays sources, from EW measurements and [*detection*]{} of unsaturated absorption lines respect $n_H$.

The paper is organized as follows: in the first section, the set of data used, next the details of the method, and finally we delineate the results of the distribution of Doppler velocities found, and compute gas densities. We also discuss the results and conclude. Throughout this paper, we use a cosmology with H$_0=70$ Mpc$^{-1}$, $\Omega_M=0.3$ and $\Omega_{\lambda}=0.7$.

The set of data and the emission continuum level \[datainput\] {#the-set-of-data-and-the-emission-continuum-level-datainput .unnumbered}
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One of the main problems in the identification of narrow spectral features in X-ray sources, is the impossibility of contrasting 