  We present long-slit optical spectra of 12 edge-on low surface brightness
galaxies (LSBGs) positioned along their major axes. After performing reddening
corrections for the emission-line fluxes measured from the extracted integrated
spectra, we measured the gas-phase metallicities of our LSBG sample using both
the [NII]/Ha and the R_23 diagnostics. Both sets of oxygen abundances show good
agreement with each other, giving a median value of 12 + log(O/H) = 8.26 dex.
In the luminosity-metallicity plot, our LSBG sample is consistent with the
behavior of normal galaxies. In the mass-metallicity diagram, our LSBG sample
has lower metallicities for lower stellar mass, similar to normal galaxies. The
stellar masses estimated from z-band luminosities are comparable to those of
prominent spirals. In a plot of the gas mass fraction versus metallicity, our
LSBG sample generally agrees with other samples in the high gas mass fraction
space. Additionally, we have studied stellar populations of 3 LSBGs which have
relatively reliable spectral continua and high signal-to-noise ratios, and
qualitatively conclude that they have a potential dearth of stars with ages <1
Gyr instead of being dominated by stellar populations with ages >1Gyr.
Regarding the chemical evolution of our sample, the LSBG data appear to allow
for up to 30 % metal loss, but we cannot completely rule out the closed-box
model. Additionally, we find evidence that our galaxies retain up to about 3
times as much of their metals compared with dwarfs, consistent with metal
retention being related to galaxy mass. In conclusion, our data support the
view that LSBGs are probably just normal disk galaxies continuously extending
to the low end of surface brightness.
