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E-Liquid Testing

To Ensure the Highest Quality E-Liquid According to Standards and Regulations

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E-Liquid Testing

Consumer demand for e-cigarettes has boomed since they were introduced in the early 2000s. While claims that e-cigarettes are a healthier choice than traditional combustion cigarettes are controversial, e-liquid testing has become essential for the development, manufacturing, and regulatory control of these popular consumables.

Quality control of e-liquids is critical for ensuring that consumers are assured of the e-cigarette or “vaping” experience they expect. E-liquid testing also helps to assure regulators and consumers that e-liquids present as advertised in terms of nicotine content, flavor, and freshness.

A variety of laboratory analyses help both in the development of desired e-liquid properties and for maintaining quality in final products. Advancements in testing and characterization will doubtlessly guide continued evolution in e-liquids production.

Select Your Field of Interest

E-Liquids Production and Testing
Characterization and Quality Control of E-Liquids
E-Liquids Manufacturing: Small-volume Filling
FAQs

 

   E-Liquids Testing in Production

eliquids production and testing

E-liquid manufacturing has created a new value chain of flavor development, blending, and distribution that includes e-liquid formulators, which are sometimes known as "e-liquid labs”. In some jurisdictions, these labs may be subject to manufacturing guidelines. This means that e-liquid testing can occur at multiple points along the distribution chain, and that these tests are conducted internally and by third-party testing labs.

E-liquid raw materials, intermediates, and final products are subject to testing. Raw materials, which are generally pharma- or food grade, are characterized for formulation. Intermediate testing ensures that e-liquid blends deliver desired characteristics. Final product testing helps to qualify and that e-liquid products meet environmental, toxicity and safety regulations as well as permissible exposure limits for Material Safety Data Sheets (MSDS).

Critical testing parameters for delivering desired “Ejuice” properties and meeting labeling requirements include nicotine content, propylene glycol/vegetable glycerin ratio (PG/VG), water content, boiling point, refractive index, density, specific gravity, and pH.

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   Characterization and Quality Control of E-Liquids

eLiquids System and Instruments

Standard lab techniques such as refractive index, UV Vis spectrophotometry and titration are useful for determining the quality and concentrations of e-liquid ingredients. Often, combining analytical techniques into a single multiparameter workflow can help in the swift grading of components and to ensure e-liquid compliance.

Properties That E-Liquid Labs Typically Test For Include:

Nicotine, the highly addictive component of tobacco smoke, is arguably the most important e-liquid ingredient for replacing cigarettes. In most countries, e-liquid nicotine content is regulated, and concentration thresholds must meet prescribed standards.

PG/VG ratio is important for vapor sensory properties including mouthfeel and sweetness. PG delivers higher flavor intensities and heavier "throat hit,” while VG provides a characteristic sweetness yet duller flavors overall. Ratio modulation also helps to fine-tune vapor cloud thickness and density, as VG’s higher viscosity requires more time and batter power to achieve optimal vaporization temperature. In most countries, PG/VG content must be declared.

Since e-liquids are vaporized during the e-smoking process, the temperature of the e-cigarette coil needs to approach the boiling point of the e-liquid. As the boiling point depends on the composition of the e-liquid, it can also be used as quality indicator.

Both propylene glycol and vegetable glycerin are hygroscopic liquids. Thus, the longer any e-liquid is exposed to humidity in air, the more its water content will increase. Water content affects the boiling point of the e-liquid and likewise vapor quality, making it less dense and providing a totally different vaping mouthfeel to the user.

These commonly measured parameters depend on e-liquid composition. Impurities as well as any shifts in ingredient quantities can change one or more parameters. Therefore, a combined measurement is ideally suited for checking the quality of final e-liquid products. With good instrumentation, these characteristics are accurately and reliably determined very quickly.

The Gardner Index is a one-dimensional color scale used to characterize yellowness of a liquid. As e-liquids containing nicotine become yellow upon aging, the Gardner Index will also increase to provide an excellent indication of quality and freshness.

pH measurement is important in e-Liquids as it can impact the flavor, aroma, and overall quality of a product. Having the right pH is important to ensure consistent taste, user safety, and product stability to ensure batch-to-batch consistency.

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E-Liquids Manufacturing: Small-volume Filling

eLiquids Testing METTLER TOLEDO

eLiquids Testing METTLER TOLEDO

E-liquid manufacturing and compliance benefits from highly accurate weighing techniques, particularly in quality checks of packaged e-liquid capsules. Smart weighing sensors in e-liquid production help to provide consistently precise results. Specialized scales with permanent airflow under the weighing pan can prevent dust and humidity from entering the weigh module interior and disrupting accuracy.

E-liquid production sites also contain a high degree of automation. Small-footprint weigh modules integrated into e-liquid machines enable precise filling of small liquid amounts to prevent over- or under-filling and meet labeling requirements. Enabled for statistical quality control (SQC), these sensors can also adjust fill quantities so that e-liquid producers work within the tightest tolerances and save money.  

Smart sensors provide also help to increase throughput by enabling shorter settling times and faster, more stable weighing results. Simply “plug and communicate” for rapid characterization, real-time diagnostics, and secure data backup.

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FAQ

Select Your Question of Interest:

  1. What Is E-Liquid?
  2. Why Test E-Liquids?
  3. Which E-Liquid Tests Are Most Important?
  4. What Regulations Guide Testing and Quality Control of E-Liquids?
  5. What Are the Typical Nicotine Levels of Ejuice?

 

1. What Is E-Liquid?

E-liquid, also called e-juice or vape juice, refers to a solution crafted for use in electronic cigarettes and other so-called vaping products. E-cigarettes simulate smoking using an electronically heated coil to vaporize e-juice for inhaling. E-liquid generally consists of vegetable glycerin (VG), propylene glycol (PG), water, glycerol, and flavoring, with VG, PG and water making up the majority of the mix. As a combustion cigarette substitute, most e-liquids also contain nicotine.

2. Why Test E-Liquids?

E-liquid testing is essential for manufacturing quality control, for new product development, and to stay abreast of regulatory requirements. While common e-liquid ingredients considered safe for ingesting have incomplete data when vaporized and inhaled, the results of e-liquid testing nevertheless have significant impacts for e-liquid quality, batch-to-batch consistency, safety, and regulatory compliance. Regulatory guidelines for e-liquid manufacturers and labs vary among countries.

3. Which E-Lliquid Tests Are Most Important?

How do multiparameter measurements improve e-liquid characterization

A series of laboratory analyses help e-liquid producers develop desired e-liquid sensory properties and also ensure quality control for final products. The most important tests tend to be nicotine content, propylene glycol/vegetable glycerin (PG/VG) ratio, boiling point, water content, refractive index, density, specific gravity, pH and Gardner Index.

Multiparameter measurements can be useful, because when only one parameter is measured, two samples can have the same value. For example, in the following graph, Texas and USA samples that contain nicotine have the same density value of 1.1127 g/cm3. However, adding refractometry results in a fast, accurate, and unique characterization of each e-liquid flavor.

4. What Regulations Guide Testing and Quality Control of E-Liquids?

The EU directive 2014/40/EU, which concerns the manufacture, presentation and sale of tobacco and related products, included e-cigarettes and e-liquids for the first time. Guideline implementation and enforcement is the responsibility of the respective EU country. For example, in Germany, producers and importers of e-liquids must receive authorization for new e-liquids by submitting a complete list of all ingredients with corresponding weight percentages. [1], [2]

E-liquids have been regulated by the United States FDA since 2016. Manufacturers and importers of e-liquids need to register their products with a complete ingredient list that includes harmful and potentially harmful constituents. [3]

[1] EUR-Lex
[2] German Federal Ministry of Food and Agriculture
[3] U.S. Food & Drug Administration (FDA)

5. What Are the Typical Nicotine Levels of Ejuice?

What are e-liquids?

Nicotine is a basic alkaloid that is naturally present in the tobacco plant. It is a psychoactive substance with both stimulant and relaxant effects and therefore an important component of most E-liquids. Commercially available e-liquids have nicotine concentrations from 3 to 18 mg/mL. Two basic applications used to accurately characterize the amount of nicotine present in vape juice are potentiometric titration and spectroscopy.

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