  Current measurements indicate that the deuterium abundance in diffuse
interstellar gas varies spatially by a factor of ~4 among sightlines extending
beyond the Local Bubble. One plausible explanation for the scatter is the
variable depletion of D onto dust grains. To test this scenario, we have
obtained high signal-to-noise, high resolution profiles of the refractory ion
TiII along seven Galactic sightlines with D/H ranging from 0.65 to 2.1x10^-5.
These measurements, acquired with the recently upgraded Keck/HIRES
spectrometer, indicate a correlation between Ti/H and D/H at the >95% c.l.
Therefore, our observations support the interpretation that D/H scatter is
associated with differential depletion. We note, however, that Ti/H values
taken from the literature do not uniformly show the correlation. Finally, we
identify significant component-to-component variations in the depletion levels
among individual sightlines and discuss complications arising from this
behavior.
