A Stability Indicating HPLC Method to Determine Actual Content and Stability of Nicotine within Electronic Cigarette Liquids

Recent advances in the analysis of electronic cigarette liquids and aerosols: Sample preparation and chromatographic characterization

Electronic cigarette (e-cigarette) usage has risen dramatically worldwide in recent years. It has been publicized as a safer alternative to the conventional combustible cigarette. This, however, has not yet been supported by robust toxicological research evidence. Analysis of the chemical compositions of e-liquids and generated aerosols is an important step in evaluating the toxicity effects of e-cigarettes. Currently, a broad spectrum of analytical methods have been employed for qualitative and quantitative analysis of chemical compositions of e-cigarette liquids and aerosols. The aim of this article is to review the advances in the chromatographic characterization of chemical composition of the latter in the recent five years. In addition, sample preparation methods for e-liquids and aerosols are surveyed and discussed. A study of the relevant literature indicates that, expectedly, gas chromatography and liquid chromatography with a variety of detection systems, particularly mass spectrometry, have been the main analytical techniques used in this field. Sample preparation procedures primarily include headspace sampling, dilute-and-shoot approach, liquid-liquid extraction and sorbent-based extraction for e-liquids and for aerosols (the latter usually with laboratory-built collection devices). Some challenges of current e-cigarette analytical research, and an overview on prospective work are also presented.

A core-molecule-shell Au@PATP@Ag nanorod for nicotine detection based on surface-enhanced Raman scattering technology

Nicotine is an addictive substance often found in tobacco and cigarette smoke and excessive exposure to it can cause various diseases. Herein, core-molecule-shell gold/4-aminothiophenol/silver nanorods (Au@PATP@Ag NRs) were prepared for quantitative detection of nicotine by using surface-enhanced Raman scattering (SERS) technology. The obtained Au@PATP@Ag NRs showed an outstanding SERS effect due to the plasticity of their morphology and the bimetallic synergistic effect between the excellent stability of Au and the highly enhanced effect of Ag. The Au@PATP@Ag NRs substrate exhibited an extremely high enhancement factor (EF) of 2.17 × 107. In addition, in-situ synthesized PATP was used as an internal standard to correct signal fluctuation and improve the reliability of quantitative nicotine detection. A wide linear dynamic range from 10-8 to 10-3 M was obtained and an ultra-low limit of detection (LOD) was about 3.12 × 10-9 M, which was superior to most of previously reported methods. This work has also been used for determining nicotine content in cigarettes and simulated environmental tobacco smoke by using a portable device. These results indicated that the developed SERS method had many potential applications in the quantitative determination of nicotine in real tobacco samples.

Chemical analysis of electronic cigarette liquids (e-liquids) and direct nicotine quantitation using surface-assisted flowing atmospheric-pressure afterglow desorption/ionization mass spectrometry (SA-FAPA-MS)

Ambient desorption/ionization mass spectrometry (ADI-MS) has been widely used for direct analysis of real samples without sample preparation or separation. Studies on the quantification of low molecular weight compounds in complex matrices with ADI-MS remain scarce. In this paper, we report the application of surface-assisted flowing atmospheric-pressure afterglow mass spectrometry (SA-FAPA-MS) for fast qualitative screening of electronic cigarette liquid (e-liquids) ingredients and direct quantification of nicotine. The quantification approach is rapid, uses a deuterated D4-nicotine standard spike, and does not require a preceding chromatography step or other methods to remove the complex sample matrix. Selected e-liquids were directly applied on thin-layer chromatography (TLC) plate surfaces (normal phase (NP) silica, reversed phase (RP) modified silica, cyano (CN) modified silica, and dimethyl (RP2) modified silica) after dilution and internal standard spiking. The plates served purely as sample carriers and no analyte separation was performed. Promising qualitative results were obtained, demonstrating the ability to detect nicotine alkaloids using this approach and the ability to differentiate e-liquids based on their flavor variations. In addition, dimethyl- (RP2-) and cyano-modified (CN-) silica surfaces were selected for quantification based on performance results of previous studies. It was shown that results were in high accordance with high-performance liquid chromatography (HPLC) experiments with lowest deviations <3% on dimethyl surfaces. Additional quantitative experiments including a certified reference material achieved equally satisfying results with lowest deviations of -1.1% from the certified nicotine content. For nicotine, detection limits down to the fmol range (96 fmol on CN and 20 fmol on RP2) were obtained. A detailed comparison of glass surfaces with functionalized surfaces showed that the functionalized surfaces were superior in terms of sample application reproducibility, mass spectra quality, sensitivity, and information density. Thus, functionalized thin-layer surfaces are considered promising tools for both qualitative and quantitative ADI-MS analysis of complex samples.

Rapid detection of nicotine and benzoic acid in e-liquids with surface-enhanced Raman scattering and artificial intelligence-assisted spectrum interpretation

Electronic cigarettes have rapidly gained acceptance recently. Nicotine-containing electronic cigarette liquids (e-liquids) are prohibited in some countries, but are permitted and simply available online in others. A rapid detection method is therefore required for on-site inspection or screening of a large amount of samples. Our previous study demonstrated a surface-enhanced Raman scattering (SERS)-based approach to identify nicotine-containing e-liquids; without any pre-treatment, e-liquid can be directly tested on our solid-phase SERS substrates, made of silver nanoparticle arrays embedded in anodic aluminium oxide nanochannels (Ag/AAO). However, this approach required manual determination of spectral signatures and negative samples should be validated in the second round detection. Here, after examining 406 commercial e-liquids, we refined this approach by developing artificial intelligence (AI)-assisted spectrum interpretations. We also found that nicotine and benzoic acid can be simultaneously detected in our platform. This increased test sensitivity because benzoic acid is usually used in nicotine salts. Around 64% of nicotine-positive samples in this study showed both signatures. Using either cutoffs of nicotine and benzoic acid peak intensities or a machine learning model based on the CatBoost algorithm, over 90% of tested samples can be correctly discriminated with only one round of SERS measurement. False negative and false positive rates were 2.5-4.4% and 4.4-8.9%, respectively, depending on the interpretation method and thresholds applied. The new approach takes only 1 microliter of sample and can be performed in 1-2 min, suitable for on-site inspection with portable Raman detectors. It could also be a complementary platform to reduce samples that need to be analyzed in the central labs and has the potential to identify other prohibited additives.

Quantitation and Stability of Nicotine in Canadian Vaping Liquids

Electronic cigarettes (e-cigarettes, vaping products) have become increasingly popular, with recent increases in use associated with closed systems delivering higher concentrations of nicotine. Most vaping products designed as an alternative to combustible cigarettes contain nicotine. A number of published studies have examined the reported concentrations of nicotine in vaping liquids (e-liquids) and found discrepancies between labelled and measured levels. Some discrepancy can also be explained by the lack of stability of nicotine in these types of products. Recently, a chemical analysis method for the quantitative determination of low and high levels of nicotine in vaping liquids was developed. This method uses dilution with acetonitrile prior to analysis with gas chromatograph mass spectrometry (GC-MS) in single ion monitoring mode (SIM). The developed method was validated using a laboratory-prepared vaping liquid as well as commercially available, nicotine-free products fortified with nicotine in the laboratory. The method detection limit (MDL) and the limit of quantitation (LOQ) for nicotine were calculated to be 0.002 mg/mL and 0.006 mg/mL, respectively. The newly developed method was applied to quantify nicotine in commercially available vaping liquids of various flavour profiles and across a wide range of nicotine concentrations, including those with nicotine salts. Furthermore, a subset of vaping liquids were analyzed to elucidate nicotine stability in various product subtypes. After a period of six months of accelerated storage to mimic one year, the overall mean percent of the original nicotine concentration remaining in the salt-based vaping products was 85% (minimum 64%, maximum 99%) while in the free-base nicotine products it was 74% (minimum 31%, maximum 106%). Nicotine stability in vaping liquids was found to be influenced by the nicotine form (pH) of formulation and its chemical composition. Non-targeted, qualitative analysis of chemical composition of vaping products showed that most constituents were identified and found to be remaining in the products following stability trials; however, three new compounds were tentatively identified in some vaping liquids at the end of the stability trials. Stability studies and the accurate quantitation of nicotine in vaping products can help inform product standards related to the safety, quality and utility of vaping products as a smoking cessation tool.

Injectable In Situ Gelling System for Sustained Nicotine Delivery as a Replacement Therapy for Smoking Cessation

Nicotine replacement therapy (NRT) is widely used to limit the withdrawal symptoms associated with cigarette smoking cessation. However, the available NRT formulations are limited by their short release profiles, requiring frequent administrations along with local side effects. Thus, the objective of this study is to develop an NRT formulation that offers prolonged, sustained nicotine release. Thermoresponsive in situ gelling systems containing nicotine were prepared using poloxamer 407 (P407) and poloxamer 188 (P188). The system was optimized using a three-factor, two-level full factorial design (23). A formulation composed of P407 (20% w/w), P188 (5% w/w), and loaded with nicotine (0.5% w/w) exhibited sol-to-gel transition at a suitable temperature close to physiological temperature (30 °C). The rheological analysis demonstrated a Newtonian-like flow at room temperature, suggesting ease of administration via injection, and semisolid gel status at physiological temperature. The optimized formulation successfully sustained nicotine in vitro release over 5 days following single administration. The findings suggest that poloxamer based in situ gelling systems are promising platforms to sustain the release of nicotine.

Nicotine in Complex Samples: Recent Updates on the Pretreatment and Analysis Method

Nicotine is a significant evaluation index of tobacco and its related products' quality, but nicotine overdose can pose serious health hazards and cause addiction and dependence, thus it can be seen that it is necessary to find suitable and efficient detection methods to precisely detect nicotine in diverse samples and complex matrices. In this review, an updated summary of the latest trends in pretreatment and analytical techniques for nicotine is provided. We reviewed various sample pretreatment methods, such as solid phase extraction, solid phase microextraction, liquid phase microextraction, QuEChERS, etc., and diverse nicotine assay methods including liquid chromatography, gas chromatography, electrochemical sensors, etc., focusing on the developments since 2015. Furthermore, the recent progress in the applications and applicability of these techniques as well as our prospects for future developments are discussed.HighlightsUpdated pretreatment and analysis methods of nicotine were systematically summarized.Microextraction and automation were main development trends of nicotine pretreatment.The introduction of novel materials added luster to nicotine pretreatment.The evolutions of ion source and mass analyzer were emphasized.

ZnO Tips Dotted with Au Nanoparticles-Advanced SERS Determination of Trace Nicotine

Long-term exposure to nicotine causes a variety of human diseases, such as lung damage/adenocarcinoma, nausea and vomiting, headache, incontinence and heart failure. In this work, as a surface-enhanced Raman scattering (SERS) substrate, zinc oxide (ZnO) tips decorated with gold nanoparticles (AuNPs) are fabricated and designated as ZnO/Au. Taking advantage of the synergistic effect of a ZnO semiconductor with morphology of tips and AuNPs, the ZnO/Au-based SERS assay for nicotine demonstrates high sensitivity and the limit of detection 8.9 × 10-12 mol/L is reached, as well as the corresponding linear dynamic detection range of 10-10-10-6 mol/L. Additionally, the signal reproducibility offered by the SERS substrate could realize the reliable determination of trace nicotine in saliva.

In vitro evaluation of the effect of the electronic cigarette aerosol, Cannabis smoke, and conventional cigarette smoke on the properties of gingival fibroblasts/gingival mesenchymal stem cells

OBJECTIVE

The current study aimed to evaluate the effect of electronic cigarette (EC) aerosol, Cannabis, and conventional cigarettes smoke on gingival fibroblast/gingival mesenchymal stem cells' (GF/G-MSCs) of never smokers.

MATERIAL AND METHODS

Human GF/G-MSCs (n = 32) were isolated and characterized using light microscopy, flow cytometry, and multilineage differentiation ability. Following the application of aerosol/smoke extracts, GF/G-MSCs were evaluated for cellular proliferation; colony-forming units (CFU-F) ability; cellular viability (using the MTT assay); mitochondrial depolarization using JC-1 dye; and genes' expression of ATM, p21, Oct4, and Nanog.

RESULTS

Colony-forming units and viability (OD 450 nm) were significantly reduced upon exposure to Cannabis (mean ± SD; 5.5 ± 1.5; p < .00001, 0.47 ± 0.21; p < .05) and cigarettes smoke (2.3 ± 1.2 p < .00001, 0.59 ± 0.13, p < .05), while EC aerosol showed no significant reduction (10.8 ± 2.5; p = .05, 1.27 ± 0.47; p > .05) compared to the control group (14.3 ± 3, 1.33 ± 0.12). Significantly upregulated expression of ATM, Oct4, and Nanog (gene copies/GADPH) was noticed with Cannabis (1.5 ± 0.42, 0.82 ± 0.44, and 1.54 ± 0.52, respectively) and cigarettes smoke (1.52 ± 0.75, 0.7 ± 0.14, and 1.48 ± 0.79, respectively; p < .05), whereas EC aerosol caused no statistically significant upregulation of these genes compared to the control group (0.63 ± 0.1, 0.31 ± 0.12, and 0.64 ± 0.46, respectively; p > .05). The p21 gene was not significantly downregulated in EC aerosol (1.22 ± 0.46), Cannabis (0.71 ± 0.24), and cigarettes smokes (0.83 ± 0.54) compared to the control group (p = .053, analysis of variance).

CONCLUSION

Cannabis and cigarettes smoke induce DNA damage and cellular dedifferentiation and negatively affect the cellular proliferation and viability of GF/G-MSCs of never smokers, whereas EC aerosol showed a significantly lower impact on these properties.

Optimization of MAE for the Separation of Nicotine and Phenolics from Tobacco Waste by Using the Response Surface Methodology Approach

This study intends to valorize by-products of the industrial processing of tobacco to obtain nicotine and phenolics as value-added compounds. Three influential parameters of the microwave-assisted extraction-MAE (temperature, treatment time, and solvent/solid ratio) were studied for the optimization of the extraction protocol for tobacco leaves and three types of waste-scrap, dust, and midrib, respectively. Nicotine was the dominant bioactive compound in all extracts, ranging from 1.512 to 5.480% in leaves, 1.886 to 3.709% in scrap, 2.628 to 4.840% dust, and 0.867 to 1.783% in midrib extracts. Five phenolic compounds were identified and quantified, predominated by chlorogenic acid and rutin. Additionally, total phenol content and antioxidant activity were determined using spectrophotometric assays. Optimization was performed in two aspects: to obtain a maximum extraction yield with minimum nicotine content and to obtain a maximum extraction yield with maximum nicotine content. These findings demonstrate that tobacco waste is a valuable source of bioactive compounds and MAE can be a promising alternative technique to obtain extracts rich in targeted bioactive compounds, especially nicotine.

Analysis of the information management system in the manufacturing process of cigarette enterprises using fuzzy AHP

In view of the production quality management of filter rods in the manufacturing and execution process of cigarette enterprises, this paper analyzes the necessity of implementing the manufacturing execution system (MES) in the production process of filter rods. In this paper, the filter rod quality system of cigarette enterprise based on MES is fully studied, and the constructive information management system demand analysis, cigarette quality control process, system function module design, implementation and test effect are given. This paper utilizes the Fuzzy analytic hierarchy process to find the optimal system for processing the manufacturing of cigarette. The implementation of MSE based filter rod quality information management system for a cigarette enterprise ensures the quality control in the cigarette production process. Through visualization, real-time and dynamic way, the information management of cigarette production is completed, which greatly improves the quality of cigarette enterprise manufacturing process.

A review of nicotine-containing electronic cigarettes-Trends in use, effects, contents, labelling accuracy and detection methods

Electronic cigarettes (ECs) are thought to be less harmful than traditional combustible cigarettes and were originally intended to help smokers quit. Over the past two decades, they have especially gained popularity with the younger generation. To date, there are over 7000 unique e-liquid flavours available and over 400 different e-cigarette brands. The accuracy of nicotine strength labelling in e-liquids was assessed in this work. Twenty-three studies from around the world were chosen to assess the level and frequency of nicotine mislabelling in 545 e-liquid products. Nicotine strengths were most commonly mislabelled by between 5% and 20%, with the majority testing lower than what the label indicated. Fifteen European e-liquids that were assessed were labelled as 20 mg/ml or less, yet when tested, they contained more than 20 mg/ml of nicotine. One e-liquid that was supposed to contain no nicotine in fact contained 23.91 mg/ml of nicotine. Furthermore, the difference between the medians of the available labelled and experimental nicotine concentrations was significant (p < 0.001, Wilcoxon signed rank test). Preliminary studies show that high nicotine levels delivered via aerosol increase the risk for nicotine poisoning and cause airway inflammation. Other EC ingredients, such as flavourings, contribute to EVALI and 'popcorn lung'. There is evidence that certain flavourings, such as menthol, reinforce the effects of nicotine and modify drug absorption and metabolism. There is a global need for better quality control in EC products in order to make these safe for consumers.

E-cigarette aerosol induced cytotoxicity, DNA damages and late apoptosis in dynamically exposed A549 cells

In this study, the acute toxicological impacts associated with electronic cigarettes consumption were determined using a novel dynamic exposure methodology. The methodology was deployed to test various e-cigarette generated aerosols in A549 cell cultures. The e-liquid chemical profiling was achieved using GC-MS analysis while toxicity of diluted e-liquids aerosols was reported using numerous cytotoxicity assays. The presented findings pointed to acute aerosol exposure (thirty puffs at 40 W of power and higher) inducing significant cytotoxic, genotoxic, and apoptotic induction in exposed cells. These findings highlighted the significant risks posed by e-cigarette usage. The proposed methodology proved to be a useful tool for future screening of e-liquids generated aerosols toxicity. Future research is needed to establish the chronic toxicity resulting from long-term e-cigarette consumption.

A systematic review of refillable e-liquid nicotine content accuracy

OBJECTIVES

The use of e-cigarettes is becoming more common in the United States. E-cigarettes are often refilled with nicotine-containing solutions of various concentrations purchased in local shops or on the Internet. There is evidence that the nicotine content in these solutions is often mislabeled; thus, we reviewed the available literature on this topic.

DATA SOURCES

We conducted a systematic review of peer-reviewed articles published worldwide on e-liquid nicotine content accuracy using the databases CAB Direct, Cochrane Central Register of Controlled Trials, PubMed, and SPORTDiscus (EBSCO).

STUDY SELECTION

Initial screening of titles and abstracts was conducted to determine relevancy for inclusion. Full-article reviews of studies involving the purchase and chemical analysis of nicotine content in refillable e-liquids were conducted for final inclusion.

DATA EXTRACTION

Data extraction included e-liquid sample size, whether the samples were labeled to contain nicotine, whether the samples were purchased in retail shops or online, and the number and percentage of samples where the analyzed nicotine content fell outside 10% of the labeled nicotine content.

RESULTS

Twenty articles described cross-sectional studies of purchased samples containing nicotine. The number of nicotine-containing e-liquid samples obtained in each study varied from 2 to 71. The percentage of samples with an analyzed nicotine concentration of more than 10% above or below the labeled nicotine concentration ranged from 0% to 100% (277/574 or 48.3%; median 46.85%). A large percentage of the samples deviated by 10% from the labeled nicotine concentrations in both U.S. and non-U.S. samples, with U.S. samples having a higher percentage.

CONCLUSION

Our review shows that actual nicotine concentrations in e-liquids may vary considerably from labeled concentrations. Pharmacists should warn patients to be wary of the contents of e-cigarettes, and explain the dangers of using these products.

Method Validation Approaches for Analysis of Constituents in ENDS

OBJECTIVE

We assessed how many peer-reviewed publications reporting chemical quantities and/or yields from electronic nicotine delivery systems (ENDS) have included adequate method validation characteristics in the publication for appropriate interpretation of data quality for informing tobacco regulatory science.

METHODS

We searched 5 databases (Web of Knowledge, PubMed, SciFinder, Embase, EBSCOhost) for ENDS publications between January 2007 and September 2018. Of the 283 publications screened, 173 publications were relevant for analysis. We identified the publications that report a certain degree of control in data quality, ie, the publications that report marginally validated methods (MVMs). MVMs refer to the methods that: (1) report 3 or more International Conference on Harmonisation (ICH) method validation characteristics, (2) state the method was validated, (3) cite their own previous publication(s) that report MVMs, or (4) use a method within the accreditation scope of an accredited laboratory.

RESULTS

Overall, 97 publications (56%) report MVMs in their studies. This percentage also reflects the publication distribution for the majority of the 28 chemicals measured by MVMs.

CONCLUSIONS

This study highlights the need for reporting sufficient validation characteristics following appropriate guidance to ensure the accuracy and reliability of the published analytical data for proper data interpretations that may support policy.

Labelling accuracy in low nicotine e-cigarette liquids from a sampling of US manufacturers

Objectives

To assess labelling accuracy for low nicotine concentration e-cigarette liquids.

Methods

Nicotine concentration in twelve e-liquids, available in 3 and 6 mg/ml strengths, was assayed (5 replicates each) using liquid chromatography–tandem mass spectrometry.

Key findings

Average nominal concentrations of nicotine were lower than reported in 23/24 products tested, with 2/12 products labelled 3 mg/ml, and 3/12 of the 6 mg/ml products showing statistically significant differences from controls.

Conclusions

Despite the emergence of a global regulatory environment for e-cigarettes, inaccuracies still exist in nicotine concentration labelling, which may affect user habits and reliability of products used in smoking cessation.

A Facile Approach for On-Site Evaluation of Nicotine in Tobacco and Environmental Tobacco Smoke

Nicotine is highly addictive and harmful. It is one of the main active ingredients in tobacco and a major pollutant in environmental tobacco smoke. Thus, it is important to detect the nicotine content in tobacco and to monitor the nicotine content in environmental tobacco smoke. However, until present, there still has been no effective device for on-site determination of nicotine content in tobacco and environmental tobacco smoke. In this work, a portable device is fabricated for sensitive on-site evaluation of nicotine in tobacco and environmental tobacco smoke based on surface-enhanced Raman scattering (SERS). The weight of the entire device is less than 1 kg, and it uses a chargeable battery to drive both the pump and the Raman spectrometer. The total analysis time can be completed within 3-5 min. Thus, it has great potential for on-site analysis of nicotine in tobacco and environmental tobacco smoke.