Although much harder to find because of the enormous background
of local (solar system) material, a few interstellar oxide grains
have recently been identified by ion microprobe measurements of
oxygen and magnesium isotopes in meteorites [ Hutcheon et al.,
1994; Huss et al., 1994]. Nittler et al. [1994]
employed a CCD (``Charge Coupled Device'') camera to quantify ion
microscope images in order to identify grains with highly anomalous
O/
O ratios. Although the method has the drawback of missing
interstellar grains which have anomalous 
O abundances but
relatively normal 
O/
O, it does permit an automated survey of
a large number of separated dust grains thereby enabling the rapid
identification of particles worthy of further detailed
investigation. With the increasing use of powerful computers for
ion microprobe data acquisition and analysis, it is likely that the
next few years will see refinement of techniques and an expansion
of applications for isotopic mapping at the few micron spatial
scale.
New areas of interest that are driving SIMS technique development are measurements of fluid inclusions [ Diamond et al., 1990, 1991] and of melt inclusions [ Sobolev and Shimizu, 1991; Dunbar and Hervig, 1992a,b; Lu et al., 1992; Metrich et al., 1993]. Because of sample heterogeneities and typically small sizes, inclusions in diamond, and mantle xenoliths in general, are good subjects for investigation by ion microprobe methods [e.g., Johnson et al., 1990; Moore et al., 1991; Rampone et al., 1991; Jerde et al., 1993a,b]. Finally, the same techniques that apply to the measurement of natural samples may be used to quantify the results of laboratory experiments, such as trace element partitioning [e.g., Jolliff et al. 1993; La Tourette et al., 1993] and dissolution [ Muir et al., 1990]. The latest machines incorporate features such as high sensitivity at high mass resolving power, high abundance sensitivity, and multicollection at high mass resolution, among others, that promise to open up new areas for investigation by SIMS.