Testing for 2,3-Pentanedione: The “Other” Diacetyl and What Every Flavor Manufacturer Must Verify

Author: R&D Team, CUIGUAI Flavoring
Published by: Guangdong Unique Flavor Co., Ltd.
Last Updated: Sep 11, 2026
WhatsApp & Telegram: +86 189 2926 7983
Email: info@cuiguai.com

2,3-Pentanedione — also known as acetylpropionyl, CAS number 600-14-6 — is the flavoring diketone that quietly replaced diacetyl across much of the e-liquid and food flavor industry, and it is the compound most likely to trip up a “diacetyl-free” claim. When brands and importers demand diketone testing, they usually ask for diacetyl and stop there. That is a gap. 2,3-Pentanedione shares diacetyl’s buttery chemistry and, according to occupational health agencies, much of its inhalation hazard profile, which is why a defensible quality program must measure it explicitly.This guide explains what 2,3-pentanedione is, how regulators and occupational health bodies treat it, which analytical methods actually detect it, and what a defensible certificate of analysis (CoA) should contain. It is written for e-liquid brand owners, importers, and technical buyers who source flavor concentrates and need laboratory-grade confidence in what their supplier ships. The short version of our advice: never accept a diketone claim without a number, never accept a number without a method, and always insist that 2,3-pentanedione is measured in the same run as diacetyl.

GC-MS is the workhorse instrumentation for quantifying 2,3-pentanedione at parts-per-billion levels

GC-MS Testing for 2,3-Pentanedione in E-Liquids and Flavor Concentrates

1. What Is 2,3-Pentanedione?

2,3-Pentanedione (IUPAC name pentane-2,3-dione; molecular formula C5H8O2; molar mass 100.12 g/mol) is a vicinal diketone — two adjacent ketone groups on a five-carbon chain. It is a clear to pale-yellow liquid with a buttery, caramel-like odor, and its flavor character is described as sweet, buttery, creamy, cheesy, and slightly toasted, with a rich baked-goods nuance. In food it is used to flavor cookies, coffee, cereal, and chocolate; in vaping it appears in sweet and creamy e-liquid profiles. The US National Institutes of Health’s PubChem record for CAS 600-14-6 lists it under the synonym acetylpropionyl and identifies it as FEMA No. 2841, the number assigned to it in the Flavor and Extract Manufacturers Association’s GRAS assessment program.

1.1 Why it became “the other diacetyl”

When diacetyl (2,3-butanedione) became publicly associated with severe flavoring-related lung disease in microwave-popcorn and flavoring workers, the industry needed a replacement for buttery notes. 2,3-Pentanedione was the obvious candidate: it smells and tastes almost identical at low doses, it was already a permitted food flavoring, and it was cheaper than rebuilding cream systems from scratch. The substitution was so widespread that 2,3-pentanedione is now found in a large proportion of sweet-flavored e-liquids on the market.The problem is that both molecules are vicinal diketones with the same reactive alpha-dicarbonyl chemistry, and the toxicological data point in the same direction. Rat studies show that inhaled 2,3-pentanedione causes fibrosis and necrosis in the respiratory tract, and mice exposed to it show increased bronchial constriction in response to methacholine challenge. The US National Institute for Occupational Safety and Health (NIOSH) investigated two facilities where it was used — a bakery mix plant in 2009 and a flavoring manufacturing facility in Kentucky in 2013 — and found elevated respiratory symptoms and abnormal lung function associated with exposure.

2. The Regulatory and Safety Picture

2.1 NIOSH treats the two diketones as one hazard family

The authoritative occupational reference is NIOSH’s Criteria for a Recommended Standard: Occupational Exposure to Diacetyl and 2,3-Pentanedione (DHHS (NIOSH) Publication No. 2016-111). The document reviews the animal and worker evidence for both compounds and proposes recommended exposure limits (RELs) at low parts-per-billion concentrations for 8-hour time-weighted averages, together with short-term limits, plus a hierarchy of controls from substitution through ventilation to respiratory protection. In practical terms, NIOSH is saying the industry should treat 2,3-pentanedione as seriously as diacetyl wherever concentrates are handled or heated.

2.2 Occupational air-testing methods exist for both compounds

For workplace air monitoring, NIOSH and OSHA have published validated sampling and analytical methods. NIOSH’s Manual of Analytical Methods (NMAM) Method 2557 covers diacetyl by gas chromatography with flame ionization detection (GC-FID), using carbon molecular sieve sorbent tubes, desorption in acetone/methanol, and a wax-phase capillary column. The method is explicitly historical — NIOSH found it underestimates diacetyl in humid air and evaluated derivatization with o-phenylenediamine as an alternative — but its documentation is valuable because it confirms the OSHA method landscape: OSHA methods 1012 and 1013 for diacetyl, and OSHA 1016 specifically for 2,3-pentanedione. These methods are for occupational exposure assessment, not finished-product testing, but they define the analytical chemistry a flavor lab should be able to replicate.

2.3 Food authorization is not inhalation authorization

A common misconception is that GRAS or EU-listed status settles the safety question for vaping. It does not. The FEMA GRAS program (which assigned 2,3-pentanedione its number 2841) evaluates flavoring substances for use in food, not for inhalation. Similarly, the European Union’s flavouring framework — Regulation (EC) No 1334/2008, whose Union list of authorised flavouring substances was established by Commission Regulation (EU) No 872/2012 — governs flavouring use in foodstuffs. Neither regime assesses chronic inhalation of heated, vaporized flavoring chemicals. In the US, e-liquids fall under the FDA’s tobacco product jurisdiction, and the National Academies of Sciences, Engineering, and Medicine’s 2018 report on the public health consequences of e-cigarettes reviewed diketones in its toxicology chapter, flagging diacetyl and 2,3-pentanedione among the constituents of concern. The regulatory conclusion for manufacturers is simple: food authorization is necessary due diligence, but it is not a substitute for inhalation-relevant toxicology or finished-product testing.

2.4 The “GRAS equals safe to vape” trap

Because 2,3-pentanedione is a permitted food flavoring, some suppliers list it openly on spec sheets while claiming full compliance, and some buyers accept that as proof of vaping safety. The trap is that the flavor is delivered differently — heated, aerosolized, and inhaled, often repeatedly over decades — a route the food-authorization process never evaluates. Any brand positioning on safety must therefore close the gap with its own data: quantified diketone levels in the liquid and in the aerosol, batch after batch.

2.5 How brands and regulators use these data

Regulators and retailers are converging on a simple expectation: the manufacturer of a flavored e-liquid should be able to state, in parts per billion, what its diketone levels are and which tests support that statement. In jurisdictions where flavor or ingredient restrictions apply to specific compounds, the declared composition and its supporting analytical data become part of a registration, notification, or premarket file, and gaps in the data trail can stall market entry. There is also a commercial use: a quantified low-diketone position is a genuine differentiator in a category where bare “diacetyl-free” claims are treated with justified skepticism. Distributors increasingly request the same three numbers — diacetyl, 2,3-pentanedione, acetoin — in every tender, so having them on file is becoming table stakes for doing business.

3. Analytical Testing: How to Measure 2,3-Pentanedione

3.1 The analytical principle

The standard approach is gas chromatography coupled to mass spectrometry (GC-MS) or GC-FID. A small, diluted sample is injected into a heated inlet, the volatile components separate on a capillary column — a polar wax-phase column is preferred for diketones because it minimizes tailing and on-column decomposition — and the detector quantifies each compound against a calibration curve built from certified reference standards. For trace work, mass spectrometry in selected-ion monitoring (SIM) mode gives the specificity needed to separate 2,3-pentanedione from co-eluting matrix components, and internal standards (often isotopically labeled analogues) correct for injection and matrix effects.

3.2 Testing the liquid versus testing the aerosol

There are two materially different questions. Liquid testing answers “what is in the bottle”: the concentrate or finished liquid is diluted in solvent (or extracted by solid-phase microextraction) and injected directly. Aerosol testing answers “what reaches the user”: a vaping machine draws puffs under defined regimes and the generated aerosol is collected on sorbent tubes, filters, or impingers, then desorbed and analyzed. The distinction matters because the two numbers can diverge substantially — some flavor compounds transfer to aerosol inefficiently, while others concentrate. The most widely cited market survey of this problem is Farsalinos and colleagues’ 2015 study in Nicotine & Tobacco Research, which tested 159 sweet-flavored e-liquids from 36 manufacturers and retailers across six European countries and the US and found diacetyl and acetylpropionyl in a large proportion of samples, many at levels above the strictest exposure-based limits.

3.3 What a defensible certificate of analysis must contain

• Method and instrumentation, including column type, detection mode, and the analytical standard used.
• Detection and quantification limits, stated for the actual sample matrix, not just the standard solution.
• Results for all three relevant compounds, diacetyl, 2,3-pentanedione, and acetoin — acetoin because it is the common lower-risk workaround and deserves its own data point.
• Calibration information, such as linear range, R2, and traceability of standards.
• Sample preparation details, including dilution factor and whether liquid or aerosol was tested.
• Batch identity and traceability, plus the signature, date, and accreditation reference of the laboratory.

3.4 Choosing a laboratory: what to look for

Not every analytical lab can quantify diketones reliably in a concentrated flavor matrix, so supplier selection deserves the same rigor as the testing itself. The practical shopping list: an ISO 17025 accreditation that actually covers the method in question; demonstrated experience with flavor concentrates and e-liquid matrices, which are demanding because of high sweetener loads, viscous carriers, and reactive diketones that degrade in hot inlets; published detection limits in the parts-per-billion range for diacetyl, 2,3-pentanedione, and acetoin; a willingness to share method details such as column phase, injection temperature, and internal standard; and batch-level reporting with fast turnaround. A lab that quotes “diacetyl only” is itself a warning sign: the same run that quantifies diacetyl costs almost nothing extra to extend to 2,3-pentanedione and acetoin, and the three numbers together are what a credible CoA needs.

Certified reference standards anchor the calibration curve behind every reported result.

Certified Analytical Standards for 2,3-Pentanedione Quantification

4. Formulating Around the Diketone Problem

4.1 The flavorist’s toolkit

Creamy, buttery, and custard-like notes can be rebuilt without high-risk diketones, but not by simply deleting an ingredient — the formula has to be re-architected. Practical levers include acetoin (itself under occupational scrutiny and therefore subject to its own reporting), butyric acid and its esters at sub-taste-threshold doses, gamma- and delta-lactones that deliver dairy-like mouthfeel, vanilla and maltol systems that mask the loss of buttery sweetness, and non-diketone cream modifiers that add viscosity and roundness in the vapor. Each substitution changes the flavor’s heat stability, oxidation behavior, and interaction with nicotine, which is why reformulation should be paired with stability and aerosol-transfer testing rather than a straight swap.

The safety-profile logic behind these substitutions — what acetoin and acetyl propionyl actually do, how they compare, and how far substitution really goes — is covered in our technical briefing on managing diacetyl substitutes and the safety profile of acetoin and acetyl propionyl. It is the closest thing to a decision tree for choosing which buttery-note builder belongs in which product.

4.2 Ketones still earn their place — with data

Ketones are irreplaceable workhorses of cream flavoring: they deliver the caramelized, slightly sour dairy edge that esters and lactones cannot fully replicate. The responsible approach is not to ban the chemical class but to know exactly which ketones are present and at what concentration. Our companion article on ketones in cream flavors and balancing buttery notes with safety in e-liquids walks through the chemistry of cream systems, the dose levels that achieve the sensory effect, and the testing regime that keeps the formula defensible.

4.3 Ingredients that work today

For brands that want low-diketone cream profiles without months of reformulation, modern concentrates are the pragmatic answer. A vanilla cream flavor concentrate built on vanilla, lactones, and maltol delivers the sweet, rounded cream character that consumers associate with vanilla custard while keeping diketone levels at or below typical reporting limits. Likewise, a carefully built milk flavor concentrate gives the dairy body and mouthfeel needed for dessert and coffee blends without leaning on acetylpropionyl. These are starting points, not endpoints: every commercial formulation should still carry its own analytical CoA.

Low-Diketone Cream Flavor Reformulation at the Flavorist Bench

Reformulation at the bench: replacing acetylpropionyl while keeping the creamy sensory signature.

5. A Testing Protocol for Brands and Importers

• Require declared diketone levels on every CoA. Do not accept “diacetyl-free” as a value; require numbers for diacetyl, 2,3-pentanedione, and acetoin.
• Audit the laboratory. Prefer ISO 17025-accredited labs and ask which methods and reference standards were used.
• Test the liquid and the aerosol. Liquid data is necessary; aerosol data is the number that reflects actual use. Budget for both.
• Set explicit thresholds. Define your ppm or ppb limits for each compound and put them in the purchase specification so they become contractual.
• Re-test on change. Every reformulation, carrier change, or new supplier lot triggers a full re-quantification, not a spot check.
• Keep retention samples. Archive samples from every batch for at least the product’s shelf life plus audit horizon.
• Build a substitution library. Pre-approved alternate flavor systems let you respond to regulatory shifts or customer demands without restarting development.
• Document the decision trail. Record what was tested, why, and by whom — defensibility in an audit depends on the paper trail, not the memory.

6. Frequently Asked Questions

• Is 2,3-pentanedione the same as diacetyl? Diacetyl is 2,3-butanedione (CAS 431-03-8); 2,3-pentanedione (CAS 600-14-6) has one additional carbon. They are closely related vicinal diketones with similar buttery odor and similar pulmonary toxicity profiles in animal and worker studies.
• Is 2,3-pentanedione banned in e-liquids? There is no blanket ban in most markets, but it is expressly scrutinized: NIOSH proposed low-ppb occupational limits covering both diketones, and many regulators and retailers impose their own concentration requirements or outright prohibitions on diketone-containing e-liquids.
• What is FEMA 2841? It is the FEMA GRAS number assigned to 2,3-pentanedione, reflecting its evaluation as a food flavoring substance. It does not authorize inhalation use.
• Which methods test for 2,3-pentanedione? GC-MS and GC-FID are standard; OSHA method 1016 covers it for workplace air, NIOSH NMAM Method 2557 documents the diacetyl analysis family, and finished products are typically quantified by GC-MS against certified standards.
• Is “diacetyl-free” labeling reliable? Not by itself. Products labeled diacetyl-free frequently contain 2,3-pentanedione or acetoin. Only quantified CoA data is reliable.
• Is testing the concentrate enough? The concentrate is the input, but the finished liquid and the generated aerosol are what the consumer actually encounters. A complete program tests all three matrices, because dilution, heating, and vaporization each change what the user inhales.
• What threshold should a brand set? There is no single universal legal limit, so most responsible brands set their own ppm or ppb thresholds based on the strictest exposure-derived guidance available, put them into the purchase specification, and enforce them contractually batch by batch.

Large-Scale Low-Diketone Cream Flavor Production and QC

Scaling from bench to batch: controlled production keeps the reformulated profile consistent.

7. Talk to a Flavor Chemist and Request Free Samples

Guangdong Unique Flavor Co., Ltd. (CUIGUAI Flavor) is a B2B flavor house serving e-liquid brands, importers, and food producers worldwide. Our R&D and QC teams can provide full analytical documentation — including quantified diacetyl, 2,3-pentanedione, and acetoin data — for every concentrate we ship, and we regularly develop custom low-diketone cream systems to customer specifications.

Contact our technical team:

📞 Phone: +86 0769 8838 0789
🌐 Website: https://www.cuiguai.com
📧 Email: info@cuiguai.com
💬 WhatsApp & Telegram: +86 189 2926 7983

Ask for a free sample kit with CoA documentation and compare the analytical data yourself. This guide is informational and is not a substitute for regulatory or toxicological advice from qualified professionals.

References

NIOSH — “Criteria for a Recommended Standard: Occupational Exposure to Diacetyl and 2,3-Pentanedione,” DHHS (NIOSH) Publication No. 2016-111. https://www.cdc.gov/niosh/publications/numbered/2016-111.html

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition — Method 2557 (Diacetyl; includes references to OSHA 1012/1013 for diacetyl and OSHA 1016 for 2,3-pentanedione). https://www.cdc.gov/niosh/docs/2003-154/pdfs/2557.pdf

PubChem CID 11747 — 2,3-Pentanedione (CAS 600-14-6; synonym acetylpropionyl; FEMA No. 2841). https://pubchem.ncbi.nlm.nih.gov/compound/11747

Wikipedia — “Acetylpropionyl” (2,3-Pentanedione: uses, safety, NIOSH investigations). https://en.wikipedia.org/wiki/Acetylpropionyl

Farsalinos KE et al. — “Evaluation of Electronic Cigarette Liquids and Aerosol for the Presence of Selected Inhalation Toxins,” Nicotine & Tobacco Research 17(2):168-174 (2015). doi:10.1093/ntr/ntu176. https://academic.oup.com/ntr/article-abstract/17/2/168/2858003

European Commission — EU Lists of Flavourings; Regulation (EC) No 1334/2008 and Commission Regulation (EU) No 872/2012 (Union list). https://food.ec.europa.eu/food-safety/food-improvement-agents/flavourings/eu-lists-flavourings_en