General Guidance for Microscopic Analysis

Microscopic examination of powdered sample material is based on observation of specific microscopic characteristics that have been established for the specific dietary supplement or food ingredient. This analysis also is used to identify some adulterants.

Identification is based on microscopic observation of cell and tissue structures of plants and animals such as:

Defined histological characteristics of plant parts (e.g. stems, roots and rhizomes, bark, leaves, flowers, seeds);

Defined histological characteristics of animal tissues and cells;

Defined staining or microscopic chemical reactions.

Identification is achieved by comparison of a representative sample from the commercial batch with authenticated or in-house working reference material, or authoritative technical descriptions of established microscopic characteristics.



Preliminary organoleptic tests may be required prior to the microscopic analysis: note and describe the color, the odor, and the taste.

The analysis depends on microscopical recognition of characteristic tissue and cell types and cell contents. In-house primary/working reference material or an authoritative technical reference description is required to compare the observation to.

While microscopes can be used in the identification of ingredients, additional quality or purity data (e.g., contamination by mold, insect, rodent hair, microbe, and economic substitution) can also be obtained from microscopy.

It is possible that finely powdered material may obliterate microscopic characteristics. In this case, other tests such as chemical assays should be employed.



The observation can be documented by means of digital or optical photographs or by descriptions.


Microscopic analysis performance standards requirement

Qualified personnel:

Personnel must be appropriately qualified to perform ingredient identification procedures including evaluation of supplier certifications, collection of wildcrafted herbs or botanicals, preparation of representative batch or lot samples, organoleptic determinations, microscopic examinations, and chemical analyses. Qualified personnel have:

Documented demonstration of knowledge, skills, and abilities pertinent to the position held;

Knowledge gained through relevant academic studies.


Equipment and supplies:

Reliable laboratory equipment, appropriate reagents, representative samples, standard reference materials, and authenticated and in-house working plant reference materials are necessary to perform required assays.

Laboratory equipment and other apparatus (e.g., microscopes, sieves, slides, cover glasses, needles, and forceps) must be suitable to perform all required tests;

Laboratory equipment is calibrated at appropriate intervals and calibrations are documented;

Reagents and reference standards are of a quality and purity appropriate for the required tests;

Authenticated and in-house working plant reference materials are of a quality appropriate for the required tests.


Laboratory quality:

Laboratory certification is documented by appropriate accrediting organization if applicable, or by monitoring in-house quality assurance performance standards.



US FDA Center for Food Safety and Applied Nutrition: Ingredient Identity Testing Records and Retention, June 1999

W. C. Evans: Pharmacognosy, 14th Edition, 542-578