For anyone who uses herbs to understand how quality is tested, the benefits and limitations of methods, and how to ensure the herbs are what they claim to be.
The issue of quality has been a problem in herbal medicine ever since trade in herbs has begun. Some of the earliest writings we have on herbal medicine include methods of authenticating herb validity and examining their quality, including several laments regarding the quality and effectiveness of those bought in the marketplaces.
As technology has advanced, so have methods of detecting adulteration and assessing quality become more refined, but so also have the methods of unscrupulous dealers looking to enhance their profits creating a constant arms race of deceit and detection. Following is a short review of the main methods of assessing quality and detecting adulteration used in the herbal medicine industry today.
Organoleptic testing
One of the simplest and most common methods of assessing the quality of herbal medicines by their effects on our senses. This method predates the written word and even the evolution of humanity, where both human and animal foragers determine the medicinal nature and potency of a herb according to their appearance, smell, texture and taste (1,2). This is still the first line of evaluating whether a plant should be picked for medicinal use among foragers and farmers, prior to further analytical testing.
Taste has played the most prominent role in determining the medicinal qualities of herbs in most major medical traditions around the world. The Charaka Samhita (c.400 BCE –200 AD), a foundational text of Ayurvedic medicine, describes six rasas (tastes) which aggravate or pacify the three doshas (principle substances) in different ways (3). Meanwhile, the Yellow Emperor’s Inner Classic and Divine Farmer’s Materia Medica (c.100–200 AD), two of the earliest classics of Chinese medicine, give descriptions of five tastes that reinforce or drain each of the main organ systems (4,5).
In addition to the regular tastes that we might recognise: bitter, sour, sweet, salty, pungent (and astringent in Ayurveda); both traditions also recognised temperature, classifying herbs as hot, cold or neutral. Their combined tastes and temperatures could determine their effects on the body. In ancient Western herbalism, tastes appear to have had a less prominent role in determining the use of a medicine but the first systematic materia medica written by Dioscorides (c. 50 AD) still uses tastes as an important factor in evaluating the quality of medicinal herbs (6), as does his contemporary Pliny the Elder in his Natural History (7).
More than just determining the correct herb from its specific taste, contemporary insights reveal that it is possible to determine some information about the chemistry of medicinal herbs from their tastes: sweet indicates the presence of sugars; sourness indicates acidity and the presence of compounds such as citric acid; bitter often indicates substances with potent effects of the body such as alkaloids, polyphenols and terpenoids; pungent indicates a significant volatile oil content; while salty herbs are likely to have a high mineral content (1,8).
Visual identification is often the first examination conducted when foraging for herbs and due to the ease of communicating this information though books and websites, it is heavily represented in the quality assessment literature. Early versions had to rely upon hand copied drawings which were time consuming and dependent on the skill of the artist, but after the invention of woodblock printing in China during the Song dynasty (11th century), the Illustrated Classic of Materia Medica (Ben Cao Tu Jing) recorded 780 medicinals with 933 drawings that were engraved onto plates for printing and wide distribution (9).
Today, most herbal guides include photographs of the herbs in their natural environment along with the cut, dried materials, accepted variants and common adulterants for comparison (10). Although these make attractive publications, their limitations are that they cannot be used for herbal materials that are processed into powders or liquids and the information on taste, smell and texture can still only be conveyed using simple written terms.
Microscopic examination
Magnification to aid visual identification began shortly after the invention of the compound microscope in the 17th century. In 1682 Nehemiah Grew published The Anatomy of Plants, the first botanical guide using a microscope to provide vivid descriptions and drawings to differentiate plants based on their minutiae (11). Today, most botanical guides also provide microscopic identification features along with macroscopic ones to facilitate identification (10).
Modern developments in microscopic technology have enhanced this further with the development of new methods to enhance the images. Methods such as phase-contrast, differential interference contrast, confocal and super-resolution microscopy, along with advances in staining agents, including fluorescence staining have led to the ability to detect ever increasing detail (12).
Physicochemical tests
Simple tests that use the unique physical and chemical properties of medicinal substances have been a part of herbal quality assessment since some of the earliest written literature. Dioscorides (c.50 CE) describes several adulteration tests to determine the authenticity of balsam (probably Balsamodendron opobalsamum) (6). He would do this by dropping a sample onto a woolen cloth and washing it out: the pure resin would wash out with no stain but the adulterants would stick. Alternatively, it could be placed in water where the pure resin would diffuse but the counterfeits would swim on top. Dioscorides provided around 40 such tests for determining the authenticity and quality of herbs (13).
Similar tests are still performed by those regularly dealing with expensive herbal ingredients. For example, there are several quick tests to determine the authenticity of saffron (Crocus sativus), a spice whose high harvest cost has earned it the nickname “red gold” (14). When placed in cold water, true saffron will float on the surface, slowly turning the entire water yellow over 10–15 minutes while the threads retain their shape and colour. Adulterants will often sink, quickly releasing a reddish colour and may dissolve. This reaction can happen faster by adding baking soda to the water and stirring the threads in, in which case the colour change should happen within seconds.
The advantage of tests like this is that they are quick, require little training and can be performed with minimal instrumentation but their simplicity also makes them relatively easy to deceive and with the value of a crop like saffron, there is plenty of economic incentive to find methods that can evade these tests, such as adding water or oil to the genuine crop to add bulk.
Chromatography
Chromatography was invented by Mikhail Tsvet in 1906, who separated chlorophyll pigments by passing an ether and alcohol extract through a calcium carbonate column (15). His discovery was largely overshadowed by the political events of the next few decades until Martin and Synge built on his work to earn the Nobel Prize for the invention of partition chromatography in 1952. Chromatography has since become an indispensable tool for analytical chemistry and the assessment of herbal medicines today.
Various forms of chromatography exist but all rely on the same principle of separating a mixture by distributing its components between two phases: a mobile phase which carries the components through a medium, and a stationary phase that remains fixed in place and causes the constituents to separate as they migrate at different speeds (16). This generates a fingerprint of individual constituents which can be compared against a known sample, or against a purified compound that is being searched for, but if an unknown compound is found, spectroscopic techniques are usually required to obtain more detailed information on its structure and enable identification.
Liquid chromatography
Liquid chromatography refers to the use of a liquid mobile phase. The liquid is pumped through a column containing the stationary phase which causes the components to elute (wash out) at different times (17). This enables the constituents to be separated, qualified and quantified as well as purified for further analysis which makes it a technique favoured in scientific literature.
There are also high performance and ultra-high performance forms of liquid chromatography which use higher pressure and resolution resulting in faster separations and greater versatility and sensitivity. While it excels at analysing samples that can be dissolved, it cannot analyse constituents that are insoluble in the commonly used solvents such as sand, silica or maltodextrin, substances which may be added as adulterants (18).
Gas chromatography
Gas chromatography uses a vaporised mobile phase which is carried by an inert gas into a stationary phase located inside a column in a temperature controlled oven which causes the constituents to elute at different rates depending on their affinity with the stationary phase (19).
Compounds can be detected using a variety of detectors including highly sensitive flame ionisation detectors, electron capture detectors, and mass spectrometers which can detect volatile compounds in very small quantities (20). This makes it useful for detecting essential oils and flavour components which can be easily affected by storage, as well as environmental pollutants such as pesticides and contamination with polycyclic aromatic hydrocarbons from nearby traffic, industrial centres or other consumers of fossil fuels.
Thin layer chromatography
Thin layer chromatography uses a thin layer of material, usually silica gel or aluminium oxide for its stationary phase (21). The mobile phase rises along the surface at a constant rate through capillary action and compounds adhere to the surface at different points depending on their relative solubility in the mobile phase and their affinity for the stationary phase. These remain in place after the mobile phase has evaporated leaving a chromatogram on the plate which can be treated by various derivatization methods to make the analytes more visible (22). This enables multiple samples to be placed on a single plate allowing comparison between samples, controls or substances of interest.
There is also a high performance version of thin layer chromatography (HPTLC) which uses automated methods, reducing human error and enabling greater separation at faster speeds for more efficient results (23). It also separates into more clearly defined bands for improved reading.
It is this high performance thin layer chromatography (HPTLC) that is of particular interest to herbal quality assessment because it can be used to develop visual fingerprints of the chemical constituents of plants that can be used for identification and the detection of adulterants by comparison to reference standards. This has facilitated the development of an HPTLC atlas of medicinal plants (24) making it the preeminent chromatographic method of quality assessment for medicinal herbs today.
It does suffer some drawbacks though, the main one being that it is mainly a qualitative method so evaluating the quantity of a compound of interest may require liquid or gas chromatography methods. It can also be deceived through the addition of purified chemical markers from a cheaper source that elute onto the plate at the same point as a desired compound and deception of this kind may require spectroscopic methods to detect (25).
Spectroscopy
Spectroscopy is the study of how radiated energy and matter interact while spectrometry is the measurement of this interaction (26). Observations on this interaction have been noted since the ancient Greek mathematician Euclid but advances in physics and technology during the 20th century have made spectroscopic techniques some of the most powerful analytical tools we possess today. The general principle is that some form of electromagnetic energy is projected at the matter being analysed which absorbs it at a specific wavelength creating an excited state. This energy is then released when it returns to its ground state.
The amount of energy absorbed or released can be observed and measured, providing detailed qualitative and quantitative information. Spectroscopy is often combined with chromatography techniques, providing a second level of analysis to the individual separated compounds. These techniques are known as “hyphenated” due to the use of hyphens in their abbreviations and provide powerful analytical tools for the examination of plants, especially in the analysis of unknown substances or uncharacterised species. The following are the spectroscopic techniques most commonly used in herbal quality assessment and research.
Ultraviolet-visible spectrophotometry
Ultraviolet-visible spectrophotometry passes light in the ultraviolet (100–400 nm) and visible (400–700 nm) spectrums through a sample and measures the wavelengths that pass through to the other side (27). Only light with a precise amount of energy can transition the atoms into an excited state causing this frequency to be absorbed and not reach the sensor. This absorption spectrum can be measured to determine the presence of a particular substance and calculate its concentration. This is a very simple form of spectroscopy to install and operate requiring only a UV-visible light source, usually a diode array, and a detector, so it is incorporated as standard on most high performance chromatography kits.
It is particularly useful in natural product research for enabling organic compounds with a high level of conjugation (the presence of alternating single and double bonds) that would ordinarily be invisible to the naked eye to become visible since increased conjugation is associated with a lower energy gap and therefore absorbing longer wavelengths of UV and visible light (28). However, it provides relatively little structural information on the substance beyond this.
Infrared spectroscopy
Infrared spectroscopy also projects light through the sample and measures its absorption, but when infrared light (780 nm – 1 mm) is absorbed by a molecule, it causes the vibrations of molecular bonds to bend or stretch in symmetric or asymmetric ways depending on the functional groups within the molecule (29). This can provide detailed information about the molecular structure, including generating a unique molecular fingerprint that can be used to identify substances.
It can be useful for a number of applications including identifying quality markers in herbal products and detecting adulteration, but it can be difficult to interpret, is sensitive to interference by water vapour which also strongly absorbs infrared light and does not provide information on the relative location of functional groups within a molecule, or its molecular weight.
Raman spectroscopy
Raman spectroscopy relies upon the principle that light scatters differently through a substance than it would incidentally due to the interaction of the light with the molecular bonds. This scattering effect, known as the Raman effect, can provide detailed information about the chemical structure and molecular interactions of a sample when a laser is projected through it.
It is becoming an increasingly popular method of assessing the quality of Chinese herbal medicines where it can authenticate raw materials, verify geographical origins, monitor active ingredient levels and detect adulteration (30). However, the Raman effect is weak, giving it a low sensitivity that can be easily swamped by fluorescence in some materials and cannot be used to detect metals (31).
Mass spectrometry
Mass spectrometry is one of the most popular techniques in natural product research. It measures the mass to charge ratio, plotted as a mass spectrum, which can reveal the elemental or isotopic signature of a molecule and enable its quantification. It achieves this by ionising the compound under investigation in order to make it susceptible to magnetic influence, then the charged ions are accelerated to a known speed and deflected using a magnetic field (32). The degree to which the magnetic field deflects the ionised molecules from their course is detected and used to determine the molecular weight.
This method can be modified by adding additional mass analysers to take multiple measurements, known as tandem mass spectrometry (MS/MS or MS2) (33). One common method is to measure the time it takes to pass between two detectors, known as their time of flight (TOF), based on the principle that heavier ions travel more slowly. Another common modification is to add oscillating electrical fields generated by four cylindrical rods (a quadrupole) which are often installed in a triple formation (QqQ) where the first selects certain ions, the second acts as a collision chamber to fragment them and the last selects the fragments to be analysed. These setups, often combined with a chromatographic separatory step, make for intimidating looking sets of initials in research papers such as HPLC-Q-TOF-MS/MS but which can be easily broken down into its respective parts.
With the high sensitivity and specificity of mass spectrometry, these setups provide an ability to identify and characterise unknown compounds which makes it an invaluable tool for basic research of previously undescribed plant compounds as well as the forensic analysis of an unknown adulterant.
However, its sensitivity also means samples need to be as pure as possible and it cannot differentiate between isomers with the same mass to charge ratio (34). It is also costly and requires operation by a specialist which puts it out of the reach of many smaller laboratories and herbal suppliers so it tends to be used by specialist food safety companies, pharmaceutical corporations and research laboratories carrying out initial research into plants to identify their constituents, which can then be detected using cheaper, simpler methods.
Nuclear magnetic resonance
Nuclear magnetic resonance is the preeminent technique for determining the structure of organic compounds and the only one in which a complete analysis and interpretation of the entire spectrum is normally expected (35). By placing molecules in a strong magnetic field, the nuclear spin can be made to align with the magnetic force. The energy transfer required to make this happen occurs at a specific wavelength that corresponds to a radio frequency which is released when the spin reverses.
This can be detected and used to provide complete structural and functional information on the molecule under investigation. This has made it an invaluable asset to herbal quality research and has important applications in detecting adulteration techniques that can evade other methods such as designer drugs (36), or analysing variability in quality along value chains (37), or detecting the addition of cheap synthetic sources of phytochemicals to genuine herb extracts (25). However, its cost is even higher than mass spectrometry, requires a larger sample size and has limited sensitivity with complex molecules (38).
Other spectroscopic techniques
Several spectroscopic techniques have a specific application in the detection of heavy metal content in herbal medicines (39). These include atomic absorption, optical emission, x-ray fluorescence and inductively coupled plasma mass spectrometry. In atomic absorption spectrometry light is projected through an atomised sample and the amount that is absorbed to transition electrons from their ground state to an excited state can determine the concentration of that particular element.
Optical emission spectrometry ignites a spark generated by an electrode contacting the sample which is in a high energy plasma state and the unique spectrum of light specific to each element that is emitted can be detected. X-ray fluorescence spectrometry relies on the principle that when a substance is bombarded with x-rays or gamma rays, its atoms become unstable resulting in the release of photons and a unique fluorescence pattern that can be used for identification and quantification.
These techniques are often used in research papers evaluating heavy metal content in herbs where concerning levels of aluminium have been detected in common herbs such as mint (Mentha spp.) and hibiscus (Hibiscus sabdariffa), enough to warrant recommendations on consumption limits (40,41). These techniques have largely become replaced with inductively coupled plasma mass spectrometry, where the sample is ionised into a plasma state and then its individual atoms separated based on their mass to charge ratio (42). This has become the benchmark standard in heavy metal detection today, due to its greater sensitivity and ability to assay for multiple elements simultaneously and has been used to raise awareness of potentially harmful levels of mercury, lead and arsenic in traditional Chinese, Ayurvedic and Tibetan medicine preparations (43), which contributed to the UK ban on the sale of unlicensed herbal medicine products from April 30, 2014 (44).
However, the equipment is expensive and requires specialist training which may make it inaccessible to most herbalists or consumers, but it can be ordered from food safety testing companies at a reasonable price if you have concerns there may be heavy metals in your supply chain.
Biological tests
Another form of testing the quality of herbal medicines which has been practiced since ancient times is that of observing their effects on a living organism. Galen (2nd century CE) complained about the quality of medicines purchased at the markets, especially the complex antivenom formula known as Theriac and proposed comparing poisoned chickens who had received the formula to ones who had not to determine if the purchased product was effective (45).
An 11th century Chinese text describes a similar method of evaluating the quality of ginseng (Panax ginseng) by comparing the breathing of a runner who had taken the root against one who had not after a race to determine its efficacy (46). The ethical implications and financial costs of running routine quality tests on animals (47) or people have meant that these sorts of tests have almost completely disappeared from formal use as evaluation tools today. Instead chemical and biological tests are used together in the initial stages of herbal medicine research to determine the therapeutic, bioactive or characteristic compounds, which can then be searched for using chemical analysis (48).
However, any herbalist or consumer who has noted that one batch or supplier seems to get better results than another has engaged in some form of post-hoc biological evaluation.
The use of in vitro assays to assess the effect of herbs on mitochondrial function has been suggested as a potential tool for evaluating the quality of herbs and to detect subtle forms of adulteration that may evade other tests (49). Since mitochondria are central to health and disease (50), the overall effect of herbs and formulas on their function may be useful in cases where the mechanisms are too complex or poorly understood.
By evaluating the end result on the mitochondrial function of a target tissue, the problem of not knowing how the many constituents may contribute to the effect is avoided, but it does have several drawbacks. It requires the composition of a database of known reproducible effects which can be difficult in biological sciences, it takes longer than chemometric analysis and can only determine if the herbs cause a desired effect, not how an adulteration may have occurred which would then have to be investigated with chemical analysis.
Genetic Barcoding
DNA barcoding revolutionised biological identification of organisms within years of its inception for forensic analysis in 1985 (51). Almost immediately, small fragments of DNA were being used to identify plants, animals and microorganisms. Small sections of genetic code are taken from an unidentified organism and compared to a reference library of verified samples. This is often faster than traditional taxonomic identification and more precise but it is only as good as the reference database, who often invest more acquiring new standards than in verifying the existing ones (52).
There is no doubt that the ability of genetic analysis to identify species and detect adulteration has been of great benefit to quality assessment of herbal medicine. It was able to prevent a ban on black cohosh (Cimicifuga racemosa syn. Actaea racemosa) when reports of liver damage began to circulate among users by determining that various Chinese species were being imported and sold as black cohosh when they were other species of Cimicifuga, Actaea or even a plant by the common name “black cohosh” in Chinese (53).
However, it does suffer from several limitations, including an inability to distinguish between different parts of the same plant which all share the same genetic code and it cannot be used on extracts and processed material where the DNA may be degraded or even absent (54). These limitations can be amplified by its own renown in authenticating herb species, such as when the New York State Attorney General attempted to cease trading of herbal supplements after testing revealed only 21% contained the herbs listed on the ingredients (55) despite the fact that a good extract should only contain the extract and not genetic material from the plant (56).
A similar position can be taken by academics familiar with the limitations of DNA barcoding too. When Duan et al. (57) analysed a medicine collected and used by the Dai ethnic group called Ha-Bin-Liang or Ha-Bin-Hao, they found only one in 27 matched the official pharmacopoeia entry of Radix Clerodendri japonicum and assumed widespread adulteration. Another possibility is that the materia medica needs updating to reflect the wide number of traditionally harvested species that may fit the original description which predates genetic analysis and even modern taxonomic classification.
Conclusion
There are many methods of assessing quality and adulteration in herbal medicines today, from simple organoleptic techniques to advanced methods of analytical chemistry and genomics. These advanced methods are really just enhancements of the basic senses, providing greater detail and precision to the observations that can be made by the senses, providing objective data readouts that can be analysed and compared to libraries of reference standards.
However, every method has its limitations and means by which it can be deceived, inviting assessors of herbal quality to use a multidimensional approach, combining several methods according to their resources and abilities. By comparing the results of multiple tests, it becomes more difficult for unscrupulous suppliers to evade all tests at once.
This review has aimed to summarise each of the main techniques with its advantages and limitations to help herbalists, suppliers and consumers understand how the tests work, which are most suitable for their needs and how to understand research papers which describe them.
References
- Weaver, R. Primitive sense and the intuitive mind: Sensory herbal medicine. Herbal Reality. 2022. Published 2022 Mar 06. Accessed 17th Jan 2025. https://www.herbalreality.com/herbalism/history/primitive-sense-intuitive-mind-sensory-herbal-medicine/
- Freymann E, Carvalho S, Garbe LA, et al. Pharmacological and behavioral investigation of putative self-medicative plants in Budongo chimpanzee diets. PLoS One. 2024;19(6):e0305219. Published 2024 Jun 20. https://doi.org/10.1371/journal.pone.0305219
- Joshi VK & Ghildiyal, S. Rasa Vimana. Charaka Samhita. Charak Samhita Research, Training and Skill Development Centre. https://doi.org/10.47468/CSNE.2020.e01.s03.002
- Unschuld, PU & Tessenow, H. Huang Di Nei Jing Su Wen: An Annotated Translation of Huang Di’s Inner Classic – Basic Questions: 2 volumes. 2011. University of California Press.
- Wilms. S. The Divine Farmer’s Classic of Materia Medica, Shen Nong Bencao Jing – 3rd Ed. 2017. Happy Goat Productions.
- Osbaldeston, TA & Wood, RPA. Dioscorides: de Materia Medica. 2000. Johannesburg: Ibidis press.
- Bostock, J & Riley, HT. Pliny the Elder, The Natural History. 1855. London: Taylor and Francis.
- Qiao K, Zhao M, Huang Y, Liang L, Zhang Y. Bitter Perception and Effects of Foods Rich in Bitter Compounds on Human Health: A Comprehensive Review. Foods. 2024;13(23):3747. Published 2024 Nov 22. https://doi.org/10.3390/foods13233747
- Liang, Z & Zhao, Z. The Original Source of Modern Research on Chinese Medicinal Materials: Bencao Texts. 2017. Alternative, Complementary & Integrative Medicine, 3, 1–9. https://doi.org/10.24966/ACIM-7562/100045
- Leon, C, & Lin, YL. Chinese Medicinal Plants, Herbal Drugs and Substitutes: An Identification Guide. 2017. London: Kew Publishing.
- Grew, N.. The Anatomy of Plants : with an idea of a philosophical history of plants : and several other lectures read before the Royal Society. 1682. Accessed 25th Sep 2021. https://archive.org/details/mobot31753000008869
- Somssich, M. A Short History of Plant Light Microscopy. Current Protocols. 2022; 2. https://doi.org/10.1002/cpz1.577
- Riddle, JM. Dioscorides on pharmacy and medicine. 1985. Austin: University of Texas Press.
- Eupherbia Canada Inc. How to Distinguish Real Saffron from Fake. 2024. Published Dec 12, 2024. Accessed 18 Jan 2025. https://eupherbia.com/blogs/blog/how-to-distinguish-real-saffron-from-fake
- Altova, E.P., Hargittai, I. Mikhail S. Tsvet—pioneer of chromatography—150 years from his birth. Struct Chem 33, 1–3 (2022). https://doi.org/10.1007/s11224-021-01804-z
- Liu, HW. Extraction and Isolation of Compounds from Herbal Medicine. In: Liu, WJH, ed. Traditional Herbal Medicine Research Methods: Identification, Analysis, Bioassay, and Pharmaceutical and Clinical Studies. Hoboken, NJ: John Wiley & Sons, Ltd. 2011:81-138.
- Excedr. What Is Liquid Chromatography? Principles, Techniques, & Applications. Published Dec 1, 2023. Accessed 19 Jan 2025. https://www.excedr.com/blog/liquid-chromatography-principles-techniques-applications
- Gafner S, Blumenthal M, Foster S, Cardellina JH 2nd, Khan IA, Upton R. Botanical Ingredient Forensics: Detection of Attempts to Deceive Commonly Used Analytical Methods for Authenticating Herbal Dietary and Food Ingredients and Supplements. J Nat Prod. 2023;86(2):460-472. https://doi.org/10.1021/acs.jnatprod.2c00929
- Turner, D. Gas Chromatography – How a Gas Chromatography Machine Works, How To Read a Chromatograph and GCxGC. Technology Networks. Published March 12, 2024. Accessed 19 Jan 2025. https://www.technologynetworks.com/analysis/articles/gas-chromatography-how-a-gas-chromatography-machine-works-how-to-read-a-chromatograph-and-gcxgc-335168
- ALWSCI Technologies. GC Vs. HPLC: A Comprehensive Comparison And Practical Applications. 2024. Published Jul 4, 2024. Accessed 19 Jan 2025. https://www.alwsci.com/news/gc-vs-hplc-a-comprehensive-comparison-and-pr-78733374.html
- Merck. Thin Layer Chromatography. Accessed 19 Jan 2025. https://www.sigmaaldrich.com/GB/en/applications/analytical-chemistry/thin-layer-chromatography
- CAMAG. Process Steps: Derivitization. Accessed 19 Jan 2025. https://camag.com/products/process-steps/#derivatization
- Haroldsen, JO. High-Performance Thin-Layer Chromatography (HPTLC). Published Jul 5, 2023. Accessed 19 Jan 2025. https://ctlatesting.com/blogs/articles/high-performance-thin-layer-chromatography-hptlc
- HPTLC Association. HPTLC Atlas. Accessed 19 Jan 2025. https://www.hptlc-association.org/atlas/hptlc-atlas.cfm
- You H, Gershon H, Goren F, Xue F, Kantowski T, Monheit L. Analytical strategies to determine the labelling accuracy and economically-motivated adulteration of “natural” dietary supplements in the marketplace: Turmeric case study. Food Chem. 2022;370:131007. https://doi.org/10.1016/j.foodchem.2021.131007
- Sapkota, A. 22 Types of Spectroscopy with Definition, Principle, Steps, Uses. Published Aug 12, 2022. Accessed 19 Jan 2025. https://microbenotes.com/types-of-spectroscopy/
- Shrestha, P. UV-Vis Spectroscopy: Principle, Parts, Uses, Limitations. Published Nov 28, 2023. Accessed 19 Jan 2025. https://microbenotes.com/uv-vis-spectroscopy/
- Ashenhurst, J. Introduction To UV-Vis Spectroscopy. Published Oct 31, 2022. Accessed 19 Jan 2025. https://www.masterorganicchemistry.com/2016/09/16/introduction-to-uv-vis-spectroscopy/
- Excedr. What Is Infrared Spectroscopy? Fundamentals & Applications. Published Jan 31, 2024. Accessed 19 Jan 2025. https://www.excedr.com/blog/what-is-infrared-spectroscopy
- Chen DD, Xie XF, Ao H, Liu JL, Peng C. Raman spectroscopy in quality control of Chinese herbal medicine. J Chin Med Assoc. 2017;80(5):288-296. https://doi.org/10.1016/j.jcma.2016.11.009
- University of Cambridge. Raman Spectroscopy > Advantages and Disadvantages. Dissemination of IT for the Promotion of Materials Science. Accessed 21st Jan 2025. https://www.doitpoms.ac.uk/tlplib/raman/advantages_disadvantages.php
- Clark, J. The Mass Spectrometer. Published Mar 2019. Accessed 19 Jan 2025. https://www.chemguide.co.uk/analysis/masspec/howitworks.html
- Allen DR, McWhinney BC. Quadrupole Time-of-Flight Mass Spectrometry: A Paradigm Shift in Toxicology Screening Applications. Clin Biochem Rev. 2019;40(3):135-146. https://doi.org/10.33176/AACB-19-00023
- Bains, B. A Beginner’s Guide to Mass Spectrometry. Published Feb 9, 2023. Accessed 19 Jan 2025. https://www.acdlabs.com/blog/a-beginners-guide-to-mass-spectrometry/
- Aryal, S. NMR Spectroscopy- Definition, Principle, Steps, Parts, Uses. Published Jan 12, 2022. Accessed 19 Jan 2025. https://microbenotes.com/nuclear-magnetic-resonance-nmr-spectroscopy/
- Patel DN, Li L, Kee CL, Ge X, Low MY, Koh HL. Screening of synthetic PDE-5 inhibitors and their analogues as adulterants: analytical techniques and challenges. J Pharm Biomed Anal. 2014;87:176-190. https://doi.org/10.1016/j.jpba.2013.04.037
- Booker A, Frommenwiler D, Johnston D, Umealajekwu C, Reich E, Heinrich M. Chemical variability along the value chains of turmeric (Curcuma longa): a comparison of nuclear magnetic resonance spectroscopy and high performance thin layer chromatography. J Ethnopharmacol. 2014;152(2):292-301. https://doi.org/10.1016/j.jep.2013.12.042
- Kaveti, B. What are the Advantages and Limitations of Nuclear Magnetic Resonance Spectroscopy? Published Aug 1 2023. Accessed 19 Jan 2025. https://www.azooptics.com/Article.aspx?ArticleID=2460
- Yuan X, Chapman RL, Wu Z. Analytical methods for heavy metals in herbal medicines. Phytochem Anal. 2011;22(3):189-198. https://doi.org/10.1002/pca.1287
- Rubio C, Lucas JR, Gutiérrez AJ, et al. Evaluation of metal concentrations in mentha herbal teas (Mentha piperita, Mentha pulegium and Mentha species) by inductively coupled plasma spectrometry. J Pharm Biomed Anal. 2012;71:11-17. https://doi.org/10.1016/j.jpba.2012.07.015
- Malik J, Frankova A, Drabek O, Szakova J, Ash C, Kokoska L. Aluminium and other elements in selected herbal tea plant species and their infusions. Food Chem. 2013;139(1-4):728-734. https://doi.org/10.1016/j.foodchem.2013.02.013
- Wilschefski SC, Baxter MR. Inductively Coupled Plasma Mass Spectrometry: Introduction to Analytical Aspects. Clin Biochem Rev. 2019;40(3):115-133. doi:10.33176/AACB-19-00024
- Martena MJ, Van Der Wielen JC, Rietjens IM, Klerx WN, De Groot HN, Konings EJ. Monitoring of mercury, arsenic, and lead in traditional Asian herbal preparations on the Dutch market and estimation of associated risks. Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2010;27(2):190-205. https://doi.org/10.1080/02652030903207235
- MHRA. Proposal to end sell-through period for unlicensed herbal medicines. Jul 12, 2013. Accessed 22 Jan 2025. https://www.gov.uk/government/consultations/proposal-to-end-sell-through-period-for-unlicensed-herbal-medicines
- Thorndike, L.. Galen: The Man and His Times. The Scientific Monthly. 1922; 14(1):83–93. Accessed 18 Jan 2024. http://www.jstor.org/stable/6569
- Shang, Z. & Gong, Y. Ben Cao Tu Jing (Atlas of Materia Medica). Published 1994. Accessed 18th Jan 2025. https://www.jameslindlibrary.org/ben-cao-tu-jing-11th-century/
- Busia, K. Perspectives on animal experimentation in herbal medicine research: ethical dilemmas and scientific progress. Journal of Herbal Medicine. 2004. 46:100903. https://doi.org/10.1016/j.hermed.2024.100903
- Li S, Han Q, Qiao C, Song J, Lung Cheng C, Xu H. Chemical markers for the quality control of herbal medicines: an overview. Chin Med. 2008;3:7. Published 2008 Jun 28. https://doi.org/10.1186/1749-8546-3-7
- Woodley, S. Mitochondrial Function as a Tool for Assessing Function, Quality and Adulteration in Medicinal Herbal Teas [PhD thesis]. University of Westminster Life Sciences. 2024. https://doi.org/10.34737/wwwvy
- Harrington JS, Ryter SW, Plataki M, Price DR, Choi AMK. Mitochondria in health, disease, and aging. Physiol Rev. 2023;103(4):2349-2422. doi:10.1152/physrev.00058.2021
- Jeffreys AJ, Wilson V, Thein SL. Individual-specific ‘fingerprints’ of human DNA. Nature. 1985;316(6023):76-79. https://doi.org/10.1038/316076a0
- Lathe, WC, Williams, JM, Mangan, ME, & Karolchik, D. Genomic Data Resources: Challenges and Promises. Nat. Educ. 2008; 1(3):2. Accessed 21 Jan 2025. https://www.nature.com/scitable/topicpage/genomic-data-resources-challenges-and-promises-743721/
- Foster, S. Exploring the Peripatetic Maze of Black Cohosh Adulteration: A Review of the Nomenclature, Distribution, Chemistry, Market Status, Analytical Methods, and Safety. HerbalGram 2013; 98, 32–51. Accessed 29 July 2024. http://cms.herbalgram.org/herbalgram/issue98/hg98feat-blackcohosh.html
- Parveen I, Gafner S, Techen N, Murch SJ, Khan IA. DNA Barcoding for the Identification of Botanicals in Herbal Medicine and Dietary Supplements: Strengths and Limitations. Planta Med. 2016;82(14):1225-1235. https://doi.org/10.1055/s-0042-111208
- James, L. A.G. Schneiderman Asks Major Retailers To Halt Sales Of Certain Herbal Supplements As DNA Tests Fail To Detect Plant Materials Listed On Majority Of Products Tested. Feb 3, 2015. Accessed 21 Jan 2025. https://ag.ny.gov/press-release/2015/ag-schneiderman-asks-major-retailers-halt-sales-certain-herbal-supplements-dna
- Morrell, A. GNC, NY AG Deal: Herbal Supplements Were In Compliance, But New Testing Requirements Instated. Forbes. Published Mar 31, 2015. Accessed 21 Jan 2025. https://www.forbes.com/sites/alexmorrell/2015/03/31/gnc-ny-ag-deal-herbal-supplements-were-in-compliance-but-new-testing-requirements-instated/
- Duan BZ, Fang HL, Li XW, Huang LF, Ping W, Chen SL. Survey of traditional Dai medicine reveals species confusion and potential safety concerns: a case study on Radix Clerodendri Japonicum. Chin J Nat Med. 2017;15(6):417-426. https://doi.org/10.1016/S1875-5364(17)30063-8
