HPLC & GC-MS: Lab Analysis for E-Liquids Explained

HPLC stands for High Performance Liquid Chromatography. In this method, a liquid sample is pumped under high pressure through a column packed with fine particulate material; individual chemical components travel through the column at different speeds depending on how strongly they interact with the packing material, which separates them from one another. A detector positioned after the column measures each substance as it exits, allowing it to be identified and quantified. HPLC is particularly well suited to compounds that don't easily vaporize or that are heat-sensitive, such as nicotine, sugars, preservatives, and other polar substances.

GC-MS combines two techniques: gas chromatography (GC) and mass spectrometry (MS). In gas chromatography, the sample is vaporized and carried by an inert gas through a thin, coated capillary column, where components separate based on their volatility and chemical affinity for the column coating. The separated substances then pass into the mass spectrometer detector, where they are ionized and identified by their characteristic fragmentation pattern — essentially a chemical fingerprint. GC-MS is therefore especially well suited to precisely identifying volatile organic compounds such as flavoring agents, residual solvents, or degradation products.

The core difference lies in the physical state used for separation: HPLC operates with a liquid mobile phase and is suited to non-volatile, polar, or heat-sensitive substances, whereas GC-MS transfers the sample into the gas phase and therefore specializes in volatile to semi-volatile compounds. Another difference concerns identification: HPLC detectors primarily rely on retention time and absorption spectra, while the mass spectrometry step in GC-MS also provides structural information. In practice, the two methods are often used together, since a single product can contain both non-volatile and volatile components.

The accurate nicotine content of an e-liquid is a key legal requirement: the EU Tobacco Products Directive (TPD, Directive 2014/40/EU) caps the maximum nicotine concentration in e-liquids at 20 mg/ml and requires accurate labeling of the actual nicotine content. Discrepancies between declared and actual nicotine levels can pose health risks to consumers and legal consequences for manufacturers and distributors alike. HPLC is widely regarded in analytical chemistry as a well-suited method for the quantitative determination of nicotine, offering precise, reproducible measurements.

Beyond nicotine content, product purity plays a decisive role in safety and compliance. GC-MS is widely used in analytical testing to detect volatile impurities such as residual solvents or unwanted degradation products — for example, carbonyl compounds (such as formaldehyde or acetaldehyde) that can form when propylene glycol and vegetable glycerin are exposed to thermal stress. Substances such as diacetyl and acetyl propionyl, found in certain flavoring agents and regulated under the TPD, can also be reliably identified using GC-MS.

E-liquids often contain complex flavor blends made up of numerous individual components such as esters, aldehydes, or terpenes. GC-MS makes it possible to identify these flavor compounds individually and match them against reference databases, revealing both the overall composition and any deviations from the declared formulation. This type of analysis helps ensure that a product's actual ingredient profile matches its legally required declarations.

EINS Labor uses HPLC and GC-MS analysis as part of its lab testing services for manufacturers and importers of e-liquids and e-cigarette products. This helps companies document the chemical composition of their products and address regulatory requirements.

For a lab result to be reliable, the underlying analytical method must be demonstrably robust. The internationally recognized ICH Q2(R1) guideline, "Validation of Analytical Procedures," defines parameters such as the limit of detection (LOD), limit of quantitation (LOQ), and recovery for this purpose. LOD indicates the lowest concentration of a substance that a method can reliably distinguish from a blank; this is typically established using a signal-to-noise ratio of at least 3:1. LOQ describes the lowest concentration that can actually be quantified with acceptable precision and accuracy, usually at a signal-to-noise ratio of 10:1. Alternatively, both values can be calculated from the calibration curve (LOD = 3.3·σ/S, LOQ = 10·σ/S). Recovery, in turn, shows how accurately a method retrieves a known amount of a substance added to a sample: in spiking experiments performed at several concentration levels, the measured amount is compared to the amount added and expressed as a percentage. Together with linearity, precision, and robustness, these validation parameters form the basis for an analytical procedure to deliver reliable, traceable results.

An international reference standard exists for the gas chromatographic determination of nicotine, propylene glycol (PG), and glycerin in e-liquids: ISO 20714:2019, "E-liquid — Determination of nicotine, propylene glycol and glycerol in liquids used in electronic nicotine delivery devices — Gas chromatographic method"; a European adoption is available as EN ISO 20714:2021. The standard describes an analytical procedure in which the diluted sample is examined using capillary gas chromatography with flame ionization detection (GC-FID). Quantification follows the internal standard method: a defined amount of a reference substance — the standard lists options including quinaldine, 1,3-butanediol, n-heptadecane, or n-octadecane — is added to the sample, and its known detector signal serves as the reference point for calculating the target analytes. High-purity helium or hydrogen is used as the carrier gas. ISO 20714 has gained practical significance in Canada in particular: the country's Nicotine Concentration in Vaping Products Regulations (SOR/2021-123) explicitly prescribe the standard as the test method for verifying compliance with the statutory nicotine limit of 20 mg/ml. As a standardized, internationally documented procedure, ISO 20714 thus provides a traceable methodological basis for the GC determination of these three central e-liquid components.

Diacetyl (2,3-butanedione) and acetyl propionyl (2,3-pentanedione) are diketone flavoring agents with a buttery, creamy taste, formerly used in caramel, vanilla, or cream flavors, among others. Inhaling diacetyl has been shown to cause bronchiolitis obliterans, an irreversible scarring and narrowing of the small airways first documented in workers in microwave popcorn manufacturing and colloquially known as "popcorn lung." For acetyl propionyl, animal studies indicate a similar potential hazard, though no confirmed human cases among e-cigarette users have been reported to date. On the regulatory side, the EU Tobacco Products Directive (2014/40/EU) does not address these substances through a fixed numerical limit but through a general risk clause: Article 20(3)(e) TPD requires that, apart from nicotine, only ingredients that pose no risk to human health, whether heated or unheated, may be used. There is no specific, EU-wide harmonized ppm limit for diacetyl. At the national, voluntary level, for example, the French standard AFNOR XP D90-300-2 sets a maximum of 22 ppm. In response to the health debate, the industry has widely moved away from these diketones voluntarily; GC-MS enables reliable detection, even below this threshold.

Why is nicotine content tested in a lab?

The declared nicotine content must match the actual content, since the EU Tobacco Products Directive (TPD) sets clear requirements and a maximum limit of 20 mg/ml. Lab testing using HPLC ensures accurate labeling and prevents consumers from being misinformed.

What's the difference between HPLC and GC-MS?

HPLC separates substances in a liquid phase and is suited to non-volatile, polar compounds such as nicotine. GC-MS transfers the sample into the gas phase and specializes in volatile compounds such as flavoring agents or residual solvents. In practice, the two methods often complement each other.

What contaminants can GC-MS detect in e-liquids?

GC-MS can detect, among other things, volatile degradation products such as carbonyl compounds (e.g., formaldehyde, acetaldehyde), residual solvents, and regulated flavoring substances like diacetyl or acetyl propionyl. These substances can arise from improper manufacturing or thermal stress.

Is lab testing legally required for every e-liquid?

Under the TPD, manufacturers and importers of e-liquids are required to accurately declare ingredients and nicotine content and to substantiate these declarations as part of the notification process. Chemical lab analysis is the standard way to document these declarations verifiably.

What does it mean if a result is reported as 'below LOQ'?

A result below the limit of quantitation (LOQ) means the substance may be present but cannot be quantified with adequate precision; the actual content falls below the method's reliably measurable threshold. Test reports typically flag such results as "< LOQ" or "not detected," depending on whether the value also falls below the limit of detection (LOD).

Is there a legal limit for diacetyl in e-liquids?

At EU level, there is no harmonized numerical limit for diacetyl; the TPD (Article 20(3)(e)) only requires that ingredients pose no risk to health. A specific threshold of 22 ppm is set by the French standard AFNOR XP D90-300-2, which is a voluntary national standard rather than EU-wide legislation.