What is the difference between substances and mixtures in safety data sheets? This question is harder to answer than it might seem at first glance. In some substance safety data sheets (SDS), Section 3 lists multiple ingredients (also called “components” in the law). On the other hand, some mixture safety data sheets only specify one ingredient: so what is correct?
Substances and mixtures – it depends on the definition
First and foremost, it is important to determine the legal framework in which you are looking to differentiate the two definitions. For safety data sheets in Europe, you will find your answer in the REACH Regulation.
Substances and mixtures in accordance with the REACH Regulation
The REACH Regulation defines “substance” and differentiates the term from “mixture” and “article”. You can find the definition in Section 3 of the regulation. A substance is a chemical element and its compounds (natural or manufactured). It includes the additives necessary to retain its stability and process-related impurities. If the substance is dissolved, the solvent only forms part of the substance if it cannot be removed without altering the substance. This point illustrates why a substance SDS can specify more than one ingredient in Section 3. The definition has another interesting aspect: The way a substance is defined also depends on the manufacturing process.
Alternative manufacturing methods mean that a substance can, for example, be listed with other impurities. Or that the specification of other ingredients is omitted. The definition of “mixture” takes this a step further: mixtures or solutions which consist of two or more substances. By contrast, an “article” is an object where the chemical composition is of less importance than its shape, surface or design. Here too, the boundaries are not always clear. The European Chemicals Agency therefore provides assistance and guidelines for differentiation. The REACH CLP helpdesk in Germany also provides support with the differentiation of articles, substances and mixtures.
Listing in the safety data sheet
In accordance with the REACH Regulation (Annex II), one of the ways to identify a substance is that sub-section 3.1 in Section 3 is used for substances. By contrast, sub-section 3.2 is used for mixtures. The component information also specifies which components must be indicated in the safety data sheet and which can be omitted. This allows you to distinguish between substances and mixtures even if several ingredients are specified in Section 3.1 or only one ingredient is listed in Section 3.2.
Sources: REGULATION (EC) No 1907/2006 (REACH Regulation), consolidated version dated 24/08/2020