We propose to continue isotopic analysis of three light elements, namely boron, carbon and nitrogen, in pristine silicate grains of Itokawa returned by the Hayabusa spacecraft using secondary ion mass spectrometry (SIMS). Preliminary studies of one grain (RA-QD02-0250) allocated to us during AO5 have revealed a carbon concentration profile consistent with solar wind implantation into the shallow layers of the grain, but the signal of 13C was too low to allow for precise quantitation of the 13C/12C ratio of the solar wind. No boron or nitrogen implantation profiles were found, potentially due to their lower cosmic abundances compared to carbon. In this continued work, although boron and nitrogen isotopes will still be measured, the primary focus is on carbon, in hopes of better quantifying the implanted solar wind 13C/12C value, from which the solar carbon isotopic composition will be inferred.