relative solar abundances as given by @1989GeCoA..53..197A.

Observations and data reduction {#sec:observations}
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We studied X-ray spectra of a sample of 33 clusters of galaxies. For a detailed description of the sample selection and data reduction see . They were selected as the most X-ray luminous clusters with more than 100ks raw exposure with the *Chandra* Advanced CCD Imaging Spectrometer [ACIS, energy range about 0.1 to 10keV, @2003SPIE.4851...28G]. The combined exposures of the sample are $\rm{\sim5.7~Ms}$ for ACIS-I and $\rm{\sim2.3~Ms}$ for the ACIS-S detectors. The redshift range of the sample is $\rm{0.025 < z < 0.45}$ with a mass range of $\rm{1\times10^{14}~M_{\odot}}$ to $\rm{2\times10^{15}~M_{\odot}}$.

The instruments spectral resolution is $\rm{\sim110-150~eV}$ which is broader than the energy difference to some neighbouring emission lines in the 3.55keV region so their influence has to be carefully modelled (see discussion in Sect. \[sec:discussion\]). We obtained the observational data from the *Chandra* data archive and reprocessed them using the standard data processing. We added all available observations for each cluster to obtain the deepest images of the systems. On the reduced images a spatial-spectral extraction was performed by using the contour binning technique `contbin` [see @2006MNRAS.371..829S], which divides the cluster emission into smaller regions of 