Detectability of x-ray absorption lines in quasar spectra

In quasar x-ray spectra it may be feasible to detect absorption features originating in hot plasma in objects that happen to lie along the line of sight. For typical parameters of the hot plasma in rich galaxy clusters and in giant-galaxy halos, such x-ray lines in the spectra of distant ordinary quasars should have an energy equivalent width under 50 eV; for them to be detectable the sensitivity of existing instruments should be improved by at least an order of magnitude. The most promising transitions in abundant heavy elements are pointed out; in certain cases they might well be sought even now with the x-ray telescope carried by the Einstein Observatory