  The elemental abundance of ICMEs and solar wind near 1 au is often adopted to
represent the abundance in the corresponding coronal sources. However, the
absolute abundance of heavy ions (relative to hydrogen) near 1 au might be
different from the coronal abundance due to the ion-proton differential speed
($V_{ip}$). To illustrate the $V_{ip}$ characteristics and explore whether it
influences the absolute abundance analysis for ICMEs and solar wind, we perform
a statistical study on the $V_{ip}$ for He$^{2+}$, C$^{5+}$, O$^{6+}$, and
Fe$^{10+}$ in both ICMEs and solar wind based on measurements of Advanced
Composition Explorer. The results show that the $V_{ip}$ is negligible within
ICMEs and slow solar wind ($<$ 400 km s$^{-1}$), while obvious in the
intermediate (400 -- 600 km s$^{-1}$) and fast wind ($>$ 600 km s$^{-1}$).
Previous studies showed that the $V_{ip}$ in ICMEs keeps negligible during
propagation from 0.3 to 5 au, but in solar wind it increases with the
decreasing heliocentric distance. Therefore, it might be questionable to infer
the absolute abundance of coronal sources through in-situ abundance near 1 au
for solar wind. Fortunately, the ion-oxygen (O$^{6+}$) differential speed
($V_{io}$) is negligible for He$^{2+}$, C$^{5+}$, and Fe$^{10+}$ within both
ICMEs and solar wind, and previous studies suggested that the $V_{io}$ does not
vary significantly with the heliocentric distance. This indicates that various
heavy ions always flow at the same bulk speed and their relative abundance
(relative to oxygen) near 1 au can represent the coronal abundance for both
ICMEs and solar wind.
