  Conventional methods to determine non-perturbative parameters in QCD, such as
the different variants of QCD sum rules or the minimal hadronic approximation,
combine a certain degree of matching to QCD with inputs from hadronic
parameters. The latter introduce systematic errors difficult to quantify. In
this paper I will apply a method based on rational approximant theory where
matching is maximized and no hadronic inputs are used, thereby leading to
simple analytical relations between high and low energy parameters. I will be
mostly interested in the phenomenological applications to the \Pi_{LR} and
\Pi_{VT} correlators, with especial emphasis on quantities like the d=6 and d=8
vacuum condensates in \Pi_{LR} or the quark condensate magnetic susceptibility
\chi_0.
