Purity of laboratory chemicals play an important role in pharmaceutical industry, especially for drug design, development and understanding of the theoretical and practical aspects of drug delivery. Numerous therapeutic compounds are developed in pharmaceutical laboratory to treat a variety of different illnesses.
Different methods of drug delivery are also studied in laboratory for a variety of formulation options. In all these cases pure laboratory chemicals are necessary.
In general, different terminologies are used to express the degree of purity of different chemicals used in laboratory. So, understanding the exact meaning of these terminologies is very important to select the grade of chemicals before purchase for laboratory. The present article discusses about the degree of purity of different laboratory chemicals, which will help to select the right chemicals for laboratory.
Grade and purity
Most, but not all, chemicals are labelled with a grade. The grade indicates the degree of purity of the chemicals. Grading of laboratory chemicals in general is not universal. It varies from country to country. For example, laboratory chemicals that conform to the requirements of the United States Pharmacopeia are graded as ‘USP’, National Formulary (NF), and the Food Chemicals Codex (FCC) etc. These products are regulated by the Food and Drug Administration of USA and all these chemicals meet the requirements necessary for their use in pharmaceutical processing and prescription compounding (USP and NF) and for use in food processing operations (FCC).
Proper quality control measures are followed during manufacturing of the laboratory chemicals. For example, NF grade chemicals are manufactured under current Good Manufacturing Practices (cGMP), meeting the requirements of the National Formulary and USP grade chemicals are manufactured under current Good Manufacturing Practices (cGMP), which meet the requirements of the US Pharmacopeia. All USP and NF Grade Chemicals meet the monograph requirements that are specified in the USP and NF grade which are the official standards for all prescription and over-the-counter medicines, dietary supplements, excipients and other healthcare products manufactured and sold in the United States.
However, there are some terminologies, which are used almost universally to describe the degree of purity of laboratory chemicals. Some of these are discussed below.
Laboratory grade: Laboratory grade or technical grade are the lowest purity and are obviously, less pure than reagent grade chemicals. These are usually used in applications where there is no requirement of official standards for lowest impurity levels and these chemicals are suitable for histology methods and general laboratory applications. Commercial grade chemicals are prepared for general industrial use.
Purity levels vary from manufacturer to manufacturer, but they're often comparable in purity to technical grade chemicals. ‘American Chemical Society (ACS) Reagent’ grade means that the chemical conforms to specifications defined by the Committee on Analytical Reagents of the American Chemical Society, but Aldrich make ‘Reagent Plus’ means more than 95 per cent pure. Laboratory grade chemicals are not pure enough to use for food, drug, or medicinal use of any kind.
Analytical Reagent (AR): Generally, ‘reagent’ means high purity chemicals for analytical use. Bottles are often labeled to show lot analysis and/or maximum limits of impurities. According to definition of ‘Analytical Reagent (AR)’- grade laboratory chemical means a chemical compound of a known high standard of purity. This purity is more than 95 per cent, in general. If the reagent also meets the requirements of the American Chemical Society Committee on Analytical Reagent, it will be denoted as an AR (ACS) reagent. AR grade reagents found in most laboratories and are used in a wide variety of analytical techniques for quality control, research and development.
Chemically Pure (CP): Laboratory chemicals of suitable purity, used for general applications are called ‘Chemically Pure’ or CP grade. These chemicals are suitable for non-critical tasks in the laboratory such as rinsing, dissolving etc.
Guaranteed Reagent (GR): It is the ideal quality for laboratory purposes. Batch to batch reproducibility is specially controlled to guarantee consistent analytical results. The grade is better than the Analytical Grade (AR). In some cases, especially depending on the manufacturers, GR grade chemicals are equivalent to AR grade.
Synthesis Reagents: The reagents suitable for organic synthesis and preparative applications are commonly called ‘Synthesis Reagents’. These consist of a broad range of chemicals. They are the key components used for transforming functional and for innovative and classical synthesis for standard transformations such as coupling, C-C/C-X bond formation, oxidation/reduction, protection chemistry, and phase transfer catalysis, halogenation, amination, homogeneous metal complex catalysts, phosphorylation etc. Some reagents are crucial in the field of chemistry and are used in large quantities. Some synthesis reagents are also used in trace amounts. Desired organic compounds are synthesized using a variety of novel reactions, catalysts, synthetic reagents and techniques in synthetic organic chemistry.
Spectroscopy Grade: Reagents viz., 2, 2, 4-Trimethylpentane with very low water content, chloroform, ethyl acetate etc., used for spectroscopy analysis is of high-purity, low residue on evaporation and produce clean UV spectrum. All these reagents are rigorously tested during and after production to ensure consistency. Spectrophotometric solvents are generally available in amber glass bottles. The reagents or solvents used for spectroscopy analysis display a high UV permeability and are subject to strict IR Spectroscopy tests. Nuclear magnetic resonance spectroscopy is the most commonly used technique in the structural analysis of compounds obtained by organic synthesis.
Dry & Anhydrous Grade: The reagents free from water or moisture are called dry or anhydrous grade. For example, acetone, acetic acid, chloroform, diethyl ether, ethanol, methanol, etc. of anhydrous grade are often used in laboratory. These reagents are ideally used for those chemical reactions where water trace inhibit or lead to side reaction and generate unwanted products. These solvents are suitable to various applications in chemical analysis, synthesis and purification. Multistep propriety manufacturing processes reduced metallic impurities, water, and peroxides content and increase percentage purity of the solvents. Generally, these are solvents applicable for analytical purposes or organic synthesis.
Dry solvents are traditionally used in water determinations according to Karl Fischer and anhydrous solvents are becoming more necessary in the new organic and inorganic chemistry research techniques. In our catalogue, you can also find extra-dry grade solvent or extra-dry with molecular sieves.
(The author is a practicing chemical engineer based in Mumbai)