Application of Liquid Chromatography Coupled to Mass Spectrometry in Quality Assessment of Dietary Supplements—A Case Study of Tryptophan Supplements: Release Assay, Targeted and Untargeted Studies

Abstract

Dietary supplements are widely consumed in the EU and the USA. Based on their similarity to pharmaceuticals, consumers mistakenly believe that dietary supplements have also been approved for safety and efficacy. However, in the absence of mandatory testing, data on supplement quality is scarce. Thus, we applied liquid chromatography coupled with tandem mass spectrometry to analyse the quality of dietary supplements containing tryptophan (Trp). We examined 22 supplements in tablets or capsules, produced in the USA, Great Britain, Germany, France, Czech Republic, and Poland. Trp release, crucial for bioavailability and efficiency, was assessed. Additionally, we performed a qualitative analysis of the main ingredient and screened for contaminants. Among the contaminants, we detected Trp’s metabolites, condensation products of Trp and carbonyl compounds, Trp degradation products, degradation products of kynurenine, and other contaminants such as glucosamine and melatonin. The main ingredient content was in the range of 55–100% in capsules and 69–87% in tablets. Surprisingly, almost no Trp release was noted from some supplements. Our study confirms the need to advance research on supplements. We believe that the high-quality analysis of supplements based on reliable analytical techniques will be an important contribution to the discussion on the regulatory framework of these products.

Dietary Supplements with Proline—A Comprehensive Assessment of Their Quality

“…The sample was prepared based on Stepien and Giebultowicz [ 21 ]. Briefly, for each supplement, we randomly selected three tablets or capsules, determined the total weight of the tablets’ or capsules’ content.…”

“…The low quality of these preparations may be a consequence of impurities [ 16 ]. Contaminants such as heavy metals [ 17 ], mycotoxins [ 18 ], insecticides [ 19 ], herbicides [ 20 ], degradation products of the main ingredient [ 21 ], and active substances such as sibutramine [ 22 ] or sildenafil [ 23 ] have often been detected in such products. Another aspect of low-quality supplements is the incorrect content of active ingredients, as shown for tryptophan [ 21 ] or melatonin [ 24 ].…”

“…Contaminants such as heavy metals [ 17 ], mycotoxins [ 18 ], insecticides [ 19 ], herbicides [ 20 ], degradation products of the main ingredient [ 21 ], and active substances such as sibutramine [ 22 ] or sildenafil [ 23 ] have often been detected in such products. Another aspect of low-quality supplements is the incorrect content of active ingredients, as shown for tryptophan [ 21 ] or melatonin [ 24 ]. In addition, if supplements are in the form of tablets or capsules, consumers expect that the substance contained in them can be released from this form at an appropriate level, thus guaranteeing the possibility of obtaining the right effect [ 25 ].…”

“…Then there is no possibility that the substance contained in the supplement will have any effect on the consumer. Low release of the substance contained in the supplement has been described in the case of supplements with tryptophan [ 21 ], lutein [ 26 ], melatonin [ 27 ], and folic acid [ 28 ]. However, the amount of data on the quality of supplements is still scarce.…”

“…In many cases, a single supplement was analysed [ 29 , 30 ]. The analysis of more than five supplements of one kind was carried out only for calcium carbonate [ 31 ], melatonin [ 27 ], folic acid [ 32 ], lutein [ 26 ] and tryptophan [ 21 ]. There are even fewer studies in which a comprehensive assessment was made: content, release, and impurities; we found such data only for tryptophan [ 21 ].…”