The identification methods of Chinese medicinal materials mainly include origin identification, morphological identification, microscopic identification, and physicochemical identification. Each method has its unique advantages and suitable objects for identification. Sometimes, it is necessary to select two or more of these methods to work together in order to accurately identify a type of Chinese medicinal material.

Traditional Chinese Medicine (TCM) is a traditional medical treatment method in China, and Chinese medicinal materials play a vital role in TCM treatment. The identification of Chinese medicinal materials involves authenticating their authenticity, quality, origin, and other aspects to ensure that the quality of Chinese medicinal materials meets standardized criteria and makes them qualified pharmaceutical products. This is a crucial step in guaranteeing the quality of Chinese medicinal materials. Identification methods for Chinese medicinal materials primarily include origin identification, morphological identification, microscopic identification, and physicochemical identification. Each method has its unique advantages and suitable objects for identification. Sometimes, it is necessary to select two or more of these methods to work together in order to accurately identify a type of Chinese medicinal material.

1. Origin Identification

Origin identification serves as the foundation of authenticating Chinese medicinal materials. It utilizes systematic taxonomy to determine the species of origin for Chinese medicinal materials, with plant-based medicines being the majority. When encountering relatively intact plant medicinal materials, botanical taxonomy knowledge is applied to directly observe their characteristics of roots, stems, leaves, and fruits through visual inspection or with the aid of external tools such as magnifying glasses and dissecting microscopes to achieve accurate identification. The sources of Chinese medicinal materials and ethnic medicines recorded in traditional herbal books and modern works are one of the contemporary bases for their use. By cross-referencing botanical taxonomy-related works and Chinese medicinal material identification works, the origin of the medicinal materials can be determined. When conditions permit, identification can also be conducted by cross-checking specimens, which involves three steps: observing morphology, verifying literature, and cross-checking specimens. Essentially, this origin refers to the species source of Chinese medicinal materials, not the variety; a single Chinese medicinal material may have several sources. Some fresh medicinal plant species with intact morphology facilitate origin identification.

2.Character Identification

Character identification is based on traditional identification experience, which is a summary of the accumulated knowledge from numerous ancient and modern physicians through long-term practice. It inherits the traditional identification experience and methods of "discriminating quality based on appearance." This method is simple and easy to implement, and the main methods used are: (1) Visual observation: Observing the shape, size, cross-section, color, and surface characteristics of Chinese medicinal materials. (2) Tactile inspection: Feeling the texture, weight, firmness, softness, maturity, and smoothness of Chinese medicinal materials with one's hands. (3) Smelling the medicinal materials: Different Chinese medicinal materials have different odors, such as the fragrant aroma of Angelica sinensis. (4) Tasting the medicinal materials: Identifying based on the specific taste of Chinese medicinal materials, such as the sweet and slightly bitter taste of Angelica sinensis. By visually inspecting the shape, size, thickness, surface texture, texture, color of the medicinal material's surface and cross-section, or the color characteristics of its internal special structures, and then combining these features with odor, taste, and other sensory inputs, one can determine the quality of the medicinal material through experience-based identification methods such as tasting, smelling, and feeling. This includes distinguishing between varieties, authenticity, freshness, maturity, wild versus cultivated, adulteration, cleanliness, water content, raw versus processed, and grade. Discriminating quality based on appearance is the essence of empirical identification, where the authenticity, authenticity, quality, and inferiority of medicinal materials are judged based on their visual characteristics. There are many descriptive characteristics for traditional character identification, such as the "star points" of rhubarb, the "clouded pattern" of Polygonum multiflorum, and the "compass pattern" of Phytolacca acinosa Roxb.

The water test method typically involves processing Chinese medicinal materials with water through soaking, wetting, and other methods. It observes the obvious or specific changes that occur when certain Chinese medicinal materials encounter water or are immersed in water to identify the authenticity, quality, and superiority of the variety. This is a very practical method that primarily includes color reaction, rotation phenomenon, hanging phenomenon, expansion reaction, floating and sinking reaction, mucus reaction, emulsification reaction, foaming phenomenon, and fluorescence reaction. For example, when safflower is soaked in water, the water turns golden yellow; when seeds like tang-le (Draba nemorosa L.) and plantago (Plantago asiatica L.) are soaked in water, their volume expands, and the surface becomes sticky and slippery; and the water extract of Cortex Fraxini (Cortex Fraxini Chinensis) exhibits a bluish fluorescent color under sunlight. The water test method utilizes the characteristics of specific reactions between individual Chinese medicinal materials and water for identification. The special components contained in the medicinal materials produce easily observable phenomena in water.

The fire test mainly involves heating and burning Chinese medicinal materials to observe various changes in the herbs, such as changes in color (of the flame, the herb, and the ash), the size of smoke, popping sounds, and changes in melting and sublimation phenomena. These phenomena are then used for identification. For example, when Dalbergia odorifera is burned, it produces black smoke and oil, leaving behind white ash; when Aquilaria sinensis is burned, it produces dense smoke and a strong aroma, along with the exudation of black oily substances; and when Lycopodium clavatum is burned, it produces popping sounds. The ancients have made excellent summaries of these distinctive characteristics, which can be used as a basis for identification.

3.Microscopic Identification

Microscopic identification is a method that utilizes a microscope to observe the tissue structure and powder characteristics of traditional Chinese medicine, and it is an important aspect of the research on the identification of traditional Chinese medicine. By observing the histological sections, powders, dissociated tissues, or surface preparations of medicinal materials, as well as the tissue structure, cell shape, or inclusions of Chinese medicinal materials in prepared formulas, the authenticity, purity, and quality of the medicinal materials can be identified. Microscopic identification methods mainly include observations of cross-sections or longitudinal sections, powder preparations, surface preparations, dissociated tissue preparations, microscopic chemical methods, and observations of prepared formulas made from powdered medicinal materials. These methods are typically applied to the identification of medicinal materials, broken medicinal materials, powdered medicinal materials, as well as traditional Chinese medicine formulations such as pills, powders, pastes, and pills, which are difficult to identify solely based on their physical characteristics.

Microscopic identification has the advantages of accuracy, rapidity, pollution-free, and simple sample processing, and is widely used in the identification of traditional Chinese medicine. It can be used for identification based on the structural characteristics of medicinal parts and the different types of cell inclusions of traditional Chinese medicine varieties. For example, the scales of Drynaria fortunei are brownish yellow or brownish red, with long or irregular-shaped body cells, with diameters ranging from 13 to 86 μm. The cell walls are slightly curved or straight, and the edges often have hairs. Two cells grow together and separate at the tip. The handle cells have irregular shapes, and the basic tissue cells are slightly lignified, with obvious pit canals and diameters ranging from 37 to 101 μm. The cuticle fragments of Sepia esculenta are quadrate-like, with vertical fine lines and transverse crack networks on the surface. Fragments with only vertical lines can also be seen. The calcareous fragments are strip-shaped, square, or irregular, often with fine stripes or branched snake-like channels.In the identification of Notoginseng and its fakes, the microscopic identification characteristics of Notoginseng powder are as follows: the powder is grayish yellow, with numerous starch grains, which are round, semi-round, or round-polygonal in shape, with diameters ranging from 4 to 30 μm. Compound grains are composed of 2 to over 10 single grains. Resin canal fragments contain yellow secretions. Ladder-veined vessels, reticulate vessels, and spiral vessels have diameters ranging from 15 to 55 μm. Calcium oxalate cluster crystals are rare, with diameters ranging from 50 to 80 μm. The microscopic characteristics of Bouvardia diffusa are that resin canal fragments are occasionally seen, containing yellow masses, and have large mucilage cells. The vessels are ladder-veined and reticulate. There are numerous starch grains, mostly single-grained, round-like or elongated oval, with diameters ranging from 10 to 20 μm, or already gelatinized. The fragments of cork tissue cells are polygonal, rectangular, or irregular, with thick walls and visible lamellar striations. Calcium oxalate cluster crystals in cortical cells and parenchyma cells have diameters ranging from 5 to 20 μm. By comparing the characteristics of starch grains, Notoginseng powder and the fake Bouvardia diffusa can be distinguished.

In recent years, the research on microscopic identification techniques has gradually deepened, with an increasing use of modern detection equipment such as digital imaging technology (microphotography), fluorescence microscopy, and polarized light microscopic identification techniques. The polarized light microscopic identification technique requires only hydration of chloral hydrate for permeabilization, which has the advantages of simple sample processing and high resolution. By establishing a microscopic identification feature database for traditional Chinese medicine varieties and utilizing intelligent scanning systems to scan and observe powdered traditional Chinese medicine preparations, features can be quickly located, improving the efficiency and accuracy of microscopic identification operations.

4.Physical and Chemical Identification

Physical and chemical identification involves using physical or chemical methods to qualitatively or quantitatively analyze the active ingredients or characteristic components contained in traditional Chinese medicine in order to authenticate the authenticity and quality of medicinal materials. The active ingredients in traditional Chinese medicine are the material basis for their pharmacological effects. Physicochemical identification methods mainly include color reaction, precipitation reaction, fluorescence method, micro-sublimation method, spectrophotometry, chromatography, expansion degree measurement, optical rotation measurement, refractive index measurement, pH measurement, acid value and saponification value measurement, moisture content measurement, ash content measurement, extract measurement, volatile oil measurement, etc. Micro-sublimation is a technique that allows certain chemical components in traditional Chinese medicine to sublime at a specific temperature, and the resulting sublimate can be observed under a microscope for its crystal shape, color, and chemical reactions. For example, micro-sublimation can be used to identify rhubarb. Microscopic chemical reactions involve observing the powder, slices, or extracts of traditional Chinese medicine placed on a slide under a microscope and observing the chemical reactions that occur after adding certain chemical reagents, such as the formation of precipitates, crystals, or specific colors. This allows the identification of the nature of cell walls and cell contents, such as the lignification and suberization of plant cell walls, the distinction between starch grains and aleurone grains, the identification of crystal types and morphological types, and the color reactions of certain chemical components. Through microscopic observation, these characteristics can be used to determine the species origin and quality of the medicinal materials. For example, in the case of Perilla frutescens leaves, by adding relevant reagents to the slide and observing the color changes of certain cells containing purple pigment in the epidermal cells, a red color appears with the addition of 10% hydrochloric acid, and a yellowish-green color appears with the addition of sodium hydroxide.

The identification of traditional Chinese medicine is the foundation for promoting the internationalization of its applications and the standardization of quality control, serving as an essential prerequisite for ensuring the safety of people's medication use. It is also an ongoing issue that has persisted throughout the thousands of years of inheritance of traditional Chinese medicine. With the continuous advancement of techniques and methods in the research of traditional Chinese medicine identification, traditional identification methods still possess significant importance. Modern identification methods in traditional Chinese medicine identification and traditional identification methods are complementary, requiring both scientific measurement of traditional identification methods with the aid of modern science and technology, as well as continuous innovation and development of new identification strategies based on traditional identification methods.

References:

[1] Wang Yanni. Development and Application of Traditional Chinese Medicine Identification Technology [J]. Modern Distance Education of Chinese Medicine and Pharmacy, 2023, 21(02): 60-63.

[2] Liu Jie, Fang Wenliang, Gu Haiyuan, et al. Identification Methods and Development Overview of Traditional Chinese Medicine [J]. Chinese Pharmaceutical Affairs, 2023, 37(11): 1332-1340.

About the Author

Xiaomichong, a pharmaceutical quality researcher, has been committed to pharmaceutical quality research and drug analysis method validation for a long time. Currently employed by a large domestic pharmaceutical research and development company, she is engaged in drug inspection and analysis as well as method validation.