  Effective methods of measuring supermassive black hole masses in active
galactic nuclei (AGN) are of critical importance to studies of galaxy
evolution. While there has been much success obtaining masses through
reverberation mapping, the extensive observing time required by this method has
limited the practicality of applying it to large samples at a variety of
redshifts. This limitation highlights the need to estimate these masses using
single-epoch spectroscopy of ultraviolet emission lines. We use ultraviolet
spectra of 44 AGN from HST/COS, IUE, and FUSE of the CIV 1549, OVI 1035, OIII]
1664, HeII 1640, CII 1335, and MgII 2800 emission lines and explore their
potential as tracers of the broad-line region and supermassive black hole mass.
The higher S/N and better spectral resolution of the Cosmic Origins
Spectrograph on Hubble Space Telescope resolves AGN intrinsic absorption and
produces more accurate line widths. From these, we test the viability of
mass-scaling relationships based on line widths and luminosities and carry out
a principal component analysis based on line luminosities, widths, skewness,
and kurtosis. At L_{1450} < 10^{45} erg/s, the UV line luminosities correlate
well with Hbeta, as does the 1450 Angstrom continuum luminosity. We find that
CIV, OVI, and MgII can be used as reasonably accurate estimators of AGN black
hole masses, while HeII and CII are uncorrelated.
