Individual RM records in the RMST provide users with a significant amount of information on the material, primarily sourced from the publicly available Certificate of Analysis (CoA) or other reports provided by the CRM producer. With the RMST, NIH ODS also curates non-provider quantitative information and citations to publications that describe the development and certification of the materials and other significant characterization and use of the materials by researchers. RM records also have assigned tags within the RMST to increase discoverability through user searches. For example, since the term “botanical” does not occur in the CoA for Cerilliant CRM S-144 Silybum Mix Solution or the associated structured data fields in the RMST (i.e., name, source, analyte group, analyte), “botanical” is assigned as one of several tags for the record so that it will still be identified via a broader search for botanical-derived materials.
RM provider informationQuantitative and qualitative data are arranged in a standardized format, and interactive display features facilitate comparisons of multiple RMs. As illustrated in Fig. 1, each RMST record includes comprehensive information for the material. In addition to the official name of the RM, common names, Latin binomials, and source parts are listed in the case of animal and plant derived materials, along with a description of the RM units (e.g., 3 vials, 1 mL each). The commercial provider (e.g., NIST, MilliporeSigma) is listed along with a hyperlink to the provider’s point of purchase website for more details. Most importantly, a sortable table is displayed of the specific analytes for which there are certified, reference, non-certified, or informational assigned values, with their respective uncertainty values where applicable.
Fig. 1The RMST user interface record display for NIST SRM 3246 Ginkgo biloba (Leaves), illustrating analyte value tables, provider hyperlinks, unit descriptions, proximate composition on the Food Matrix Triangle, and material Identity/Authenticity information
Users can toggle the table’s displayed content by selecting tabs for different analyte groups, such as elements, vitamins, amino acids, alkaloids, isoflavones, curcuminoids, and fatty acids. The categorization of analyte groups is primarily derived from the nomenclature in the RM provider’s CoA, for example, the classification of NIST SRM 3247 Ginkgo biloba (Extract) analytes as either flavonoids, proximates, terpene lactones, or toxic elements. In some circumstances, analyte group and analyte names have been standardized for the purposes of their listing in the RMST. A material’s CoA might list either “arsenic” or “As” or either “vitamin K1” or “phylloquinone” as measurands, which are listed in the RMST as “arsenic (As)” and “vitamin K1 (phylloquinone),” respectively. Importantly, a CoA’s use of descriptive measurand terminology that indicates a particular analytical approach is reflected in RMST records. For example, distinct thyroglobulin measurements in the record for NIST SRM 1949 Frozen Human Prenatal Serum are reported as “thyroglobulin (by LC–MS/MS)” and “thyroglobulin (by immunoassay).”
Materials that consist of multiple levels or compositions are presented as multiple individual records, one for each level/composition. For example, a commercial unit of NIST SRM 3275 Omega-3 and Omega-6 Fatty Acids in Fish Oil consists of two vials each of three different oils. In RMST, SRM 3275 is organized as three separate records appended as Part 1, Part 2, and Part 3. This approach allows users to readily view and more easily discern the differences in analytes and assigned values between the RM components.
Dietary ingredient and food RM compositionA well-known limitation in the use of RMs for dietary supplement and food analyses is the lack of matrix matched RMs for all ingredients and products of interest. To help users assess whether an available RM might be representative of the analytical challenges encountered in the determination of micronutrients, phytochemicals, or contaminants in their investigational ingredient or product, records for those RMs that have value determinations for total carbohydrate, total fat, and total protein will display a visual representation of the RM’s proximate composition on a model of the AOAC International “Food Matrix Triangle” previously developed to help define RMs applicable to the analysis of foods [11, 12]. This Food Matrix Triangle charts carbohydrate, fat, and protein percentages on a nine-sector triangle, where each of the main triangle’s three points represents 100% of one component and the opposite side represents 0% of that same component. An interactive “Search Similar Matrices” filter function enables users to identify other materials among the current search results that have determined macronutrient compositions within a specified standard deviation from the selected RM’s mean values for protein, fat, or carbohydrates. After clicking the “Search Similar Matrices” icon and link, users are prompted to set a filter for limiting the search to within either 0.5, 1, 1.5, 2, 2.5, or 3 standard deviations of the currently selected RM values for protein, fat, or carbohydrate (Fig. 2). These Food Matrix Triangle plots provide a means to quickly search and visualize where one RM can have a similar macronutrient composition to another RM, an important feature of the RMST that facilitates more informed comparison and selection of RMs relevant to researchers’ interests.
Fig. 2Highlight of the RMST “Search Similar Matrices” feature to identify other CRMs or RMs whose carbohydrate, protein, and fat mass fraction composition is within a set number of standard deviations from the current RM record
Identity/authenticity informationEstablishing identity and authenticity is a critical step in RM development. This is especially true for RMs intended to support the characterization of plant-based foods and botanical dietary supplements, as the source plants can exhibit significant chemical variation depending on their geographic location, environment, and harvest and preparation conditions. Where a provider’s CoA or other documentation describes unique details of an RM’s sourcing and preparation, the corresponding RMST record will display a brief text summarizing those details as Identity/Authenticity Information. The RMST record for NIST RM 8650 Ground Kudzu (Pueraria montana var. lobata) Rhizome, for example, displays text describing how the source material was harvested from Boone County, West Virginia, USA, and that taxonomic identity was established by a trained botanist. Such information is derived from the official Report of Investigation for RM 8650.
Non-provider informationThe RMST also serves as a resource for identifying chemical characterization data generated by analysts other than the RM provider, termed “Non-Provider Information” in an RM record’s data table. Non-Provider Information can include data where NIH ODS has worked with non-provider organizations to fill gaps in profiling either toxic elements or proximates for existing RMs. To date NIH ODS has collaborated with the US Food and Drug Administration (FDA) Center for Food Safety and Applied Nutrition to fill gaps in value assignments for the four major toxic elements in dietary supplement SRMs and RMs [13]. NIH ODS has also contracted with the Eurofins Nutrition Analysis Center (Des Moines, IA, USA) to measure total carbohydrate, total fat, and total protein content in botanical dietary supplement ingredient RMs that are representative of plant biomass, such as NIST SRM 3246 Ginkgo biloba (Leaves), SRM 3250 Saw Palmetto (Serenoa repens) Fruit, and SRM 3299 Ground Turmeric (Curcuma longa L.) Rhizome. The additional determinations for toxic elements and proximates were conducted to support more comprehensive comparisons between the available dietary supplement RMs, which researchers can use to better select appropriate control materials for method development or quality assurance efforts. Future updates of RMST records may include citations to additional non-provider analytical characterization results that are reported in peer-reviewed scientific literature, government reports, or application notes from RM producers.
PublicationsIn the course of producing an RM, providers often publish reports detailing their development. The RMST provides hyperlinks to such peer-reviewed publications in scientific journals, application notes, and NMI reports in a record’s Publications tab when available. Publication hyperlinks in the RMST direct users to either a publication’s Digital Object Identifier (DOI, www.doi.org), its PubMed ID (https://pubmed.ncbi.nlm.nih.gov/), or a publisher’s URL. The primary intent of NIH ODS in curating these selected publication references is to support users in gathering more information on the material’s sourcing, preparation, value assignment, and certification process. Additional publication types may also be added to the RMST as these CRMs and RMs are further characterized in research studies, such as the metabolomic analyses by Kellogg et al. [14] of NIST SRM 3254 Green Tea (Camellia sinensis) Leaves and SRM 3256 Green Tea-Containing Solid Oral Dosage Form.
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