Development of reference materials for dietary supplements-analytical challenges, use, limitations, and future needs.

For two decades, the National Institute of Standards and Technology (NIST) and the National Institutes of Health Office of Dietary Supplements have collaborated to develop dietary supplement-matrix reference materials. During the first decade, NIST developed over 20 botanical and non-botanical dietary supplement Standard Reference Materials (SRMs^®) using multiple analytical techniques to assign values for selected marker compounds and toxic elements. In the past decade, NIST has expanded the scope of materials available, and other producers of certified reference materials (CRMs) have joined to provide a limited number of additional materials. This review describes briefly the first decade in the development of CRMs for dietary supplements, primarily botanical dietary supplement ingredients (e.g., ginkgo, green tea, saw palmetto, St. Johns' wort, botanical oils, berries, and soy) and a popular multivitamin/multimineral (MVM) SRM. We discuss the analytical challenges in producing these materials and how these materials established a model for the next generation of CRMs. The second generation of dietary supplement CRMs/RMs, consisting primarily of botanical matrices, calibration solutions, and new and replacement MVM CRMs, is discussed in greater detail including improvements based on experiences from the first decade and potential future needs and developments in this emerging reference material research sector.