  We present the first results of the application of the recently found
universality of behavior of muon signal to electromagnetic (EM) signal ratio
with respect to the vertical depth of showers maximum for mass composition and
hadronic interaction studies. Making use of the fact that for zenith angles
above 45 degrees the dependence of the ratio on the vertical depth of shower
maximum is very similar for QGSJET II and EPOS 1.99 we show that this provides
the possibility to estimate muon shower content in almost interaction model
independent way. To evaluate the excess of signal in the data in respect to
Monte-Carlo predictions we propose to use mass independence of the
electromagnetic signal. Using the simulations with EPOS 1.99 as a fake data we
show that one can determine the absolute scaling factor between these fake data
and the interaction model under test (QGSJET II in our case). Applying this
scaling factor to the total and muon signals of QGSJET II one can make accurate
conclusions on the primary mass of samples prepared with EPOS 1.99.
