Pei Chen, a chemist with the ARS food-composition lab, headed a study of the differences between phytochemicals in green tea supplements and green tea leaves used for brewing beverages. Green tea-based dietary supplements have gained popularity in the U.S. market in recent years. But when it comes to sipping green tea versus taking the dietary supplement form, the jury is out as to the better choice relative to health. HRMS can be very useful in identifying the differences.