ACS citation is commonly used in chemistry, chemical engineering, biochemistry, and related science courses.
It helps students cite journal articles, books, lab manuals, patents, websites, and other technical sources clearly. Unlike APA or MLA, ACS gives writers more than one accepted in-text citation method, so the first step is knowing which version your instructor wants. This guide explains ACS citation rules, examples, and common mistakes to check before submitting your paper.
Quick Answer to ACS Citation
ACS citation is the citation style of the American Chemical Society. It is widely used in chemistry and related scientific fields. ACS allows three common in-text citation methods:
ACS Method | In-Text Example | Reference List Order |
|---|---|---|
Superscript numbers | Catalysts improved the reaction yield.¹ | Numbered by first citation |
Italic numbers in parentheses | Catalysts improved the reaction yield (1). | Numbered by first citation |
Author-date | Catalysts improved the reaction yield (Smith, 2023). | Alphabetical by author |
Many chemistry assignments and ACS journals use numbered citations. In that system, the first source cited is 1, the second source is 2, and repeated sources keep the same number.
ACS author guidelines direct writers to use The ACS Style Guide and ACS reference guidance for journal papers, books, and other publications.
What Is ACS Citation?
ACS citation is a documentation style designed for chemical and scientific writing. It tells writers how to cite sources in the text and how to format the References list at the end of a paper.
ACS style is different from general academic styles because chemistry writing often cites technical journal articles, chemical methods, experimental data, patents, standards, and specialized handbooks. A clear ACS citation helps readers locate the exact study, reaction method, dataset, or source that supports a scientific claim.
Students usually use ACS citation in:
general chemistry papers
organic chemistry lab reports
biochemistry assignments
chemical engineering papers
research proposals
journal article summaries
scientific literature reviews
If your instructor says “use ACS style,” ask whether they want superscript numbers, italic numbers in parentheses, or author-date citations.
How ACS In-Text Citations Work
ACS permits three main in-text citation systems. The University of Texas at Tyler’s ACS guide summarizes these as superscript numbers, italic numbers in parentheses, and author-date format.
Superscript Numbers
Superscript numbers are common in ACS journal writing. The citation number is raised above the text line.
Example:
Recent studies show that palladium catalysts can improve cross-coupling efficiency.¹
The number points to the matching reference in the References list.
Italic Numbers in Parentheses
Some courses use italic numbers in parentheses instead of superscripts.
Example:
Recent studies show that palladium catalysts can improve cross-coupling efficiency (1).
This system still uses numbers in the order sources first appear.
Author-Date Citations
ACS also allows an author-date system.
Example:
Recent studies show that palladium catalysts can improve cross-coupling efficiency (Nguyen and Patel, 2023).
This version looks more like APA, but ACS reference formatting is still different. Use author-date only if your instructor or journal asks for it.
How the ACS References List Works
In the numbered ACS systems, the References list is arranged in the order sources first appear in your paper. The first source cited is reference 1, the second new source is 2, and so on. If you cite the same source again later, reuse the original number.
In the author-date system, references are usually alphabetized by author.
A student paper usually places the source list at the end under the heading References. A university ACS handout notes that ACS reference entries are numbered sequentially in order of appearance and commonly use a hanging indent.
ACS Citation Format by Source Type
Source Type | Basic ACS Reference Format |
|---|---|
Journal article | Author 1; Author 2. Article Title. Abbreviated Journal Title Year, Volume (Issue), Pages. DOI. |
Book | Author. Title of Book; Publisher: Place of Publication, Year. |
Book chapter | Author. Chapter Title. In Book Title; Editor, Ed.; Publisher: Place, Year; pp pages. |
Website | Author or Organization. Title of Page. Website Name. URL (accessed Month Day, Year). |
Patent | Inventor. Title of Patent. Patent Number, Date. |
ACS journal references often use abbreviated journal titles. In chemistry writing, journal abbreviations are important because many references use standard short forms.
Complete ACS Citation Example
Here is a complete ACS example for a chemistry journal article.
Source information:
Authors: Maria L. Garcia and Thomas Chen
Article title: Nickel-catalyzed reduction of aryl halides
Journal: Journal of Organic Chemistry
Year: 2023
Volume: 88
Issue: 14
Pages: 9120–9128
DOI: 10.1021/acs.joc.example
Sentence in the paper:
Nickel catalysts have been used to reduce aryl halides under mild conditions.¹
Reference entry:
Garcia, M. L.; Chen, T. Nickel-Catalyzed Reduction of Aryl Halides. J. Org. Chem. 2023, 88 (14), 9120–9128. https://doi.org/10.1021/acs.joc.example
This example is correct because the in-text citation uses the number 1, and the matching reference entry is also numbered 1. The authors are listed with last names and initials. The article title appears before the abbreviated journal title. The year is bold, the volume is italicized, the issue appears in parentheses, and the page range follows. The DOI is included because it helps readers locate the article.
If this same source is cited later, it should still be cited as 1, not assigned a new number.
ACS Book Citation Example
Reference entry:
Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry: Part A: Structure and Mechanisms, 5th ed.; Springer: New York, 2007.
In-text citation:
Reaction mechanisms often depend on both electronic effects and steric factors.²
This citation includes the authors, book title, edition, publisher, place of publication, and year. Book titles are italicized in ACS style.
ACS Website Citation Example
Reference entry:
American Chemical Society. ACS Publications Author Guidelines. https://researcher-resources.acs.org/publish/author_guidelines (accessed June 26, 2026).
In-text citation:
ACS provides author guidelines for preparing manuscripts and references.³
For websites, include the author or organization, page title, website or page information, URL, and access date. Access dates matter because online content may change.
ACS Journal Article vs. APA Journal Article
ACS and APA both cite journal articles, but they format them differently.
Element | ACS | APA |
|---|---|---|
In-text citation | Superscript number or (1) | (Author, Year) |
Author format | Garcia, M. L.; Chen, T. | Garcia, M. L., & Chen, T. |
Article title | Usually title case | Sentence case |
Journal title | Abbreviated and italicized | Usually full and italicized |
Year placement | After journal title | After author |
Reference order | Numbered or alphabetical, depending on system | Alphabetical |
A common student mistake is using APA punctuation in an ACS paper. If your assignment requires ACS numbered style, do not write (Garcia, 2023) in the text. Use the required ACS number format instead.
Common ACS Citation Mistakes
Mistake | Correct Approach |
|---|---|
Mixing ACS citation systems | Choose superscript, italic-number, or author-date and use it consistently. |
Giving the same source a new number | Reuse the original number when citing the source again. |
Alphabetizing a numbered ACS reference list | In numbered ACS systems, list sources by first appearance. |
Forgetting journal abbreviations | Use accepted abbreviated journal titles when required. |
Omitting DOI information | Include the DOI for journal articles when available. |
Using APA author punctuation | Follow ACS author formatting with semicolons between authors. |
Forgetting access dates for websites | Include the date you accessed online sources when required. |
Citing a database record instead of the article | Cite the actual journal article, not only the database page. |
Tips for Checking ACS Citations Before Submitting
First, confirm which ACS in-text system your instructor wants. This one decision affects your entire paper. A paper using superscript numbers should not suddenly switch to author-date citations halfway through.
Next, check the order of your references. If you use a numbered ACS system, reference 1 should be the first source cited in the text. Reference 2 should be the second new source cited. Repeated sources should keep their original numbers.
Then review each reference entry closely. Check author initials, journal abbreviations, year, volume, issue, page range, DOI, URL, and access date. Chemistry citations often include many small details, and small formatting errors can make a source harder to find.
Finally, compare your final list with your course guide or ACS examples. Different instructors may simplify ACS style for class assignments, but consistency and complete source information are always important.
FAQ About ACS Citation
What is ACS citation?
ACS citation is the citation style of the American Chemical Society. It is used mainly in chemistry, chemical engineering, biochemistry, and related scientific fields.
What are the three ACS citation systems?
The three common ACS systems are superscript numbers, italic numbers in parentheses, and author-date citations. Use the system required by your instructor or journal.
Is ACS citation the same as APA?
No. APA uses author-date citations. ACS may use numbered citations or author-date citations, and its reference entries follow chemistry-specific formatting rules.
Is an ACS reference list alphabetical?
It depends on the system. Numbered ACS reference lists are arranged in the order sources first appear. ACS author-date reference lists are usually alphabetical.
How do you cite a journal article in ACS?
A typical ACS journal article citation includes authors, article title, abbreviated journal title, year, volume, issue, page range, and DOI when available.
Do ACS citations need access dates for websites?
Usually, yes. Website citations commonly include the URL and the date accessed because online content may change.
Conclusion
ACS citation is designed for chemistry and related scientific fields, where journal articles, lab methods, patents, and technical sources are common. The most important step is choosing the correct ACS in-text system and using it consistently. Before submitting your paper, check that every in-text citation matches the References list, journal titles are abbreviated correctly, repeated sources keep the same number, and each source includes the details readers need to find it.