A

absorption Removal of a particular molecule from a sample by accumulation into a bound water volume such as might be present in a densely fibrous material. Compare to adsorption.

accelerated stability tests Studies in which the product is stored under stress conditions (for example, 45 °C and high humidity over three to six months) and observed for signs of degradation; used to predict long-term storage patterns.

ACN Acetonitrile; the most frequently used solvent in HPLC, commonly used as an eluent.

acidic variant A product variant that exhibits a more negative charge character by IEX or CE than the primary biotherapeutic form.

active starting material The raw material that is identified as directly related to the active chemical comprising the product, and is defined at the first stage during chemical synthesis at which part or most of the critical moieties are present. Defining active starting material defines the step at which compliance with cGMP requirements begins during manufacturing. For biopharmaceuticals, this term is not used.

acute Describes a disorder as a one-time condition (an injury or infection), rather than as a chronic disease such as diabetes.

ADME Absorption, distribution, metabolism, and excretion

ADR Adverse drug reaction, an undesirable effect that may be caused by a study drug (see also adverse events).

adsorption Adherence of molecules in solution or suspension to cells or other molecules—or to solid surfaces, such as chromatography media. Compare to absorption.

adventitious agents Acquired, accidental contaminants in a cell line, such as viruses and toxins; often infectious agents.

adverse events (see also ADR) Undesired effects or toxicity in a patient due to exposure (often to a drug or medical device, but not limited to those). Adverse events must be notified to the sponsor, who is required to perform a written investigation into the root causes, and may need to take other corrective or preventive actions. (See complaints, CAPA)

aerobic Growing in the presence of oxygen. A strict aerobe grows only under such a condition.

affinity Attraction between particles or substances; relatively speaking, a measure of the attraction of one molecule toward another.

affinity chromatography A chromatographic method that makes use of the specific binding of one molecule to another; immunoaffinity chromatography uses antibodies, for example, and metal affinity chromatography uses chelation.

affinity tag (or tail) An amino acid sequence added to a protein to facilitate purification by affinity chromatography.

agarose A polysaccharide (sugar) obtained from seaweed and used as a solidifying agent (agar) in microbial culture; also used in gel electrophoresis.

One of the most frequently used solvents in chromatographic analysis is ACN, acetonitrile.

Ala Alanine; one of more than 20 naturally occurring amino acids.

albumins Protein constituents of blood plasma and serum also found in muscle, egg white, and milk.

alkylation The introduction, by substitution or addition, of an alkyl group into an organic compound; alkylating agents are various substances that contain an alkyl radical and that can, therefore, replace a hydrogen atom in an organic compound; alkylation is used to prevent refolding of already reduced proteins during peptide mapping.

alpha helix (a-helix) A coil or spiral element of protein secondary structure.