Determination of key secondary metabolites
Manufacturers rely on the quality of the laboratories that analyze their products. Contracting a laboratory that holds ISO/IEC 17025 accreditation, covering the compounds that need testing, offers assurance for the manufacturer. These laboratories should use ISO/ IEC 17034 accredited reference materials if they are available and participate in PT schemes for compounds within the laboratory’s accredited scope [37]. Reference materials play a crucial role in ensuring the accuracy, precision, and recovery of the testing process - encompassing methods, equipment, and staff performance. Beyond this, they are integral to ongoing daily system suitability checks, quality controls, calibration, and training. Therefore, securing high-quality reference standards from a reputable and knowledgeable supplier, such as LGC Standards, is critical. Manufacturers can trust certificates for reference standards that are issued by accredited laboratories, especially those maintaining ISO/IEC 17034 [37]. The importance of high-quality reference standards and reported an average value of 5.06% CBD, with a spread of results, assessed by the reproducibility standard deviation, of 0.056%. Using these criteria to assess the performance of the participant laboratories, the acceptable range of results was 4.94 – 5.17%, within which 83% of the participants were assessed as satisfactory. Participating laboratories’ performance in determining elemental contamination in herbal supplements was similarly good. In this PT, those taking part were required to analyse samples of a herbal supplement for concentrations of the ‘big four’ toxic elements: arsenic, cadmium, lead and mercury. At concentrations ranging from 0.25 to 1.4 ppm (mg/kg), participant performance was considered satisfactory if the result obtained was within ±20% of the assigned value. Using these criteria, 75%, 86%, 73%, and 73% of the participants were assessed as satisfactory for arsenic, cadmium, lead, and mercury respectively.
The determination of key secondary metabolites in herbal supplements involves a variety of methods that have evolved alongside advancements in analytical equipment. Current techniques include thin layer chromatography (TLC), infra-red spectroscopy (IR), near infra-red spectroscopy (NIR), High Performance- Thin Layer Chromatography (HP-TLC), high- performance liquid chromatography (HPLC) with various detectors (ultraviolet, diode array, and mass spectrometry), as well as gas chromatography (GC) coupled with suitable detectors, such as flame ionisation detectors, and mass spectrometry.
Contaminants
Whilst the methods and techniques described previously are widely used to determine components influencing the ‘quality’ or ‘efficacy’ of a supplement or medicinal herb, a number of parameters are routinely measured to identify the presence of unacceptable concentrations of a range of contaminants. The diverse nature of supplements results in a wide range of production processes that can potentially lead to the presence of contaminants, while natural products may also absorb toxic elements from the environment during growth or processing. Microorganisms are another significant concern, especially in herbal supplements as, apart from the direct infection risk, some microorganisms may produce toxins (mycotoxins) that pose both poisoning and carcinogenic hazards.
PT performance in supplements
LGC AXIO Proficiency Testing offers schemes in several different fields of measurement and analysis, including environmental and industrial testing, as well as foods and beverages. AXIO schemes such as PHARMASSURE include samples that are relevant to the supplements industry, including test materials for the identification and quality testing of herbal supplements and preparations, while the CANNABIS scheme is designed for laboratories determining the efficacy and composition of cannabis and cannabis preparations. The AXIO PHARMASSURE scheme provides dedicated samples for the analysis of cannabidiol (CBD) in supplements, as well as toxic elements in herbal supplements. Several rounds have now been completed for each sample material, typically with good performance recorded by the participants. The most recent round for the determination of CBD in a tincture, effectively an efficacy determination, was a material with a label claim of 5% CBD. Participants exclusively used HPLC methodology for the analysis
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