U.S. Food and Drug Administration’s Total Diet Study: How improved analytical methods affect monitoring data

Abstract

In 2014, the U.S. Food and Drug Administration’s (FDA) Total Diet Study (TDS) began updating the digestion/extraction and the determinative methods for nutrient and toxic elements. The analytical methods for iodine, manganese, and selenium were all updated to inductively-coupled plasma mass spectrometry (ICP–MS) from colorimetric determination, inductively-coupled plasma atomic emission mass spectrometry (ICP–AES), and hydride generation atomic absorption spectrometry (HGAAS), respectively. With updates in digestion/extraction and determinative methods, new limits of detection (LODs) and limits of quantitation (LOQs) were determined. The changes in methods for iodine, manganese, and selenium analysis were evaluated by determining the proportion of results above the LOQ, below the LOD (non-detects or NDs), and between the LOD and LOQ (trace values), in data generated before and after the changes. Selenium showed little change in the proportion of NDs, higher proportions of trace values, and lower proportions of results above the LOQ. Iodine and manganese had lower proportions of NDs and trace values and higher proportions of results above the LOQ. Updating methods can have various effects on data and potentially how data are utilized. These results indicate that these new methods are an improvement on the old methods and validate the changes made to the methodology.