  We analyze spectra for a large sample of 578 Active Galactic Nuclei to
examine the relationships between broad emission line properties and central
supermassive black hole (SMBH) mass. We estimate SMBH masses by applying the
virial theorem to the C IV lambda 1549 broad emission line. Although the FWHMs
of C IV and H beta appear nearly unrelated in individual objects, these FWHMs
are well correlated when averaged over sub-samples in our database. Therefore,
the lines are equally valid indicators of the average SMBH mass in quasar
samples. Our sample spans five orders of magnitude in SMBH mass, six orders of
magnitude in luminosity, and a redshift range from 0 <= z <= 5. Most lines
diminish in equivalent width with increasing black hole mass (the usual
"Baldwin Effect") and there are no trends with redshift. Recent studies
indicate that there is a relationship between SMBH mass and the overall
bulge/spheroidal component mass of the surrounding galaxy. This relation,
together with the well-known mass-metallicity relationship among galaxies,
predicts a relationship between SMBH mass and quasar metallicity. We estimate
the metallicity in the broad emission line region by comparing several line
ratios involving nitrogen to theoretical predictions. We find that the data are
consistent with a trend between SMBH mass and metallicity, with some line
ratios indicating a very strong trend, but the uncertainties in several other
important line ratios are too large to confirm or test this correlation.
