Jerrold Mitchell will be the new CIO of the $680 million Boston Foundation. He retired in October as CIO of the $36.1 billion Massachusetts Pension Reserves Investment Management Board, Boston. Mr. Mitchell will work with the foundation's consultant, Prime, Buchholz & Associates, in overseeing the fund's asset allocation and monitoring its money managers, he said. "Other than maybe making some minor adjustments, I don't expect there to be any major changes to the plan's investments," he added. He replaces James Pitts, who retired late last year.