Numeric Citations in ACS Referencing

ACS referencing offers a couple of methods for citing sources in the chemical sciences. This includes a number–note system, where you cite sources using numbers in the text. But how do numeric citations work in ACS referencing? In this blog post, we run you through the basics.

Numeric Citations Styles in ACS Referencing

The number–note version of ACS referencing offers two options for how to cite sources:

• One that uses superscript numbers to indicate citations.
• One where you use italicized numbers in brackets to cite sources.

You may, therefore, need to check which version your client is using if you’re proofreading a document that uses ACS referencing. But these systems work in broadly the same way, with each number corresponding to an entry in a reference list at the end of the document:

Superscript: The results show a significant improvement.¹

Italic Numbers: The results show a significant improvement (1).

In addition, both versions require authors to number sources in the order they’re first cited (i.e., the first source cited in a document will be “1,” the second “2,” the third “3,” and so on). The author will then use the same number each time they cite a source, preventing repetition.

Naming the Author in the Text

If your client names an author in the text in ACS referencing, they should give the accompanying citation immediately afterwards. For instance:

Superscript: Herman¹ claims that the results show a significant improvement.

Italic Numbers: Herman (1) claims that the results show a significant improvement.

In addition, if a source has two authors, they should be joined with “and”:

Superscript: Smith and Jones² achieved similar results in a later test.

Italic Numbers: Smith and Jones (2) achieved similar results in a later test.

And for sources with more than three authors, ACS suggesting using “et al.” (a Latin term meaning “and others”) after the first author’s name to save space:

Superscript: Harris et al.³ were initially skeptical.

Italic Numbers: Harris et al. (3) were initially skeptical.

All authors should be named in the reference list, along with full publication information.

Citing Multiple Sources at Once

ACS referencing also allows authors to cite more than one source at once.

For consecutive sources (i.e., sources listed sequentially in the reference list), this simply requires using an en dash between the first and last source cited:

Superscript: The results caused significant debate over the following year.^8–11

Italic Numbers: The results caused significant debate over the following year (8–11).

In the examples above, for instance, we’re citing sources 8, 9, 10 and 11 from the reference list.

For non-consecutive sources, source numbers should be separated with commas. The presentation differs slightly between systems here, though. For superscript citation numbers, ACS suggests using unspaced commas between source numbers:

Superscript: This theory has been tested repeatedly without success.^1,4,8

But for italicized numbers, there should be a space between each source:

Italic Numbers: This theory has been tested repeatedly without success (1, 4, 8).

Finally, to cite more than one source by the same principal author working with different co-authors, give the first author’s name followed by “and co-workers” or “and colleagues”:

Superscript: Harris and colleagues^1,10–14 have run multiple tests to confirm this.

Italic Numbers: Smith and co-workers (19–23) produced a lot of evidence.

Keep an eye out for this when proofreading papers in chemistry as it is easy to miss.

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Referencing Style or System? A Guide for the Confused A Quick Guide to DOIs and URLs How to Spot a Credible Source