  Correlations obtained from sequences of measurements have been employed to
distinguish among different physical theories or to witness the dimension of a
system. In this work we show that they can also be used to establish
semi-device independent lower bounds on the purity of the initial quantum state
or even on one of the post-measurement states. For single systems this provides
information on the quality of the preparation procedures of pure states or the
implementation of measurements with anticipated pure post-measurement states.
For joint systems one can combine our bound with results from entanglement
theory to infer an upper bound on the concurrence based on the temporal
correlations observed on a subsystem.
