Elsevier

Forensic Science International

Volume 266, September 2016, Pages 549-554
Forensic Science International

Elemental and molecular profiling of licit, illicit, and niche tobacco

https://doi.org/10.1016/j.forsciint.2016.07.023Get rights and content

Highlights

  • FTIR and XRF are useful analytical techniques for tobacco identification.

  • Elemental profiles highlight Ca, Cl, K and Fe as indicators of tobacco provenance.

  • FTIR identifies a highly discriminative tobacco spectral fingerprint region.

Abstract

The recognition of differences between regulated large-scale mass manufactured products and the uncontrolled cultivation of tobaccos for illicit purposes plays a significant role within identification of provenance. This research highlights X-ray fluorescence and Fourier transform infrared spectroscopy as useful analytical techniques for the rapid identification of tobacco samples of unknown provenance. Identification of key discriminative features within each technique allowed for the development of typical characteristic profiles for each type of tobacco. Analysis using X-ray fluorescence highlights chlorine, potassium, calcium and iron as key elemental indicators of tobacco provenance. Significant levels of chlorine seen within Snüs samples prompted attempts to visualise chlorine containing regions and structures within the sample. Scanning electron microscopy images showed crystalline structures visible within the Snüs tobacco, structures which Energy dispersive X-ray spectroscopy qualitatively confirmed to contain chlorine. Chloride levels within Snüs samples were quantified using ion chromatography with levels found to range between 0.87 mg mL⿿1 and 1.28 mg. Additionally, FTIR indicated that absorbances attributed to carbonyl stretching at 1050⿿1150 cm⿿1, alkane bending at 1350⿿1480 cm⿿1 and amide I stretching at 1600⿿1700 cm⿿1 highlighting a spectral fingerprint region that allowed for the clear differentiation between different types of tobaccos using PCA analysis, but was limited by differentiation between provenance of cigarettes and hand rolled tobacco. X-ray fluorescence and Fourier transform infrared spectroscopy yielded different information with regards tobacco discrimination and provenance, however both methods overall analysis time and cost reduced indicating usefulness as potential handheld analytical techniques in the field.

Introduction

Illicit tobacco is typically sold in the form of cigarettes or hand rolled tobacco, which is grouped by U.K. trading standards and Her Majesty⿿s Revenue and Customs (HMRC) into two main groups: counterfeit products, or ⿿Cheap Whites⿿ [1], [2]. Counterfeit tobacco products mimic licit brand packaging in an attempt to masquerade as licit products and contain low-grade unregulated tobacco, which is sold to unsuspecting consumers. In comparison, ⿿Cheap Whites⿿ are cigarettes that utilize poor filters and low grade tobacco marketed under illicit brand names purely targeted for sale to the U.K. illicit market [1].

Niche tobacco products vary drastically in content depending on the desired method of ingestion, where the product can be consumed without full or any pyrolysis [3]. Niche tobacco is a source of licit tobacco from another country consistently prohibited from sale on the U.K. market. These products do not typically meet standards set out in U.K. or European legislation due to limited knowledge of adverse health effects and contents information [3]. Niche tobacco has over time increased in popularity all over the world, predominantly due to the nature of socialization associated with its use [4], [5].

Many of the chemical substances that are associated with the tobacco plant are attributed to atmospheric depositions or the application of phosphate fertilizers and sewage sludge [6], [7]. The International Agency for Research on Cancer has highlighted tobacco as a major source of known cancer causing heavy metals with such as cadmium and lead. These heavy metals are found within the body adipose tissues after long term accumulation and are linked to life threatening non-cancerous toxicity of the cardiovascular and renal systems [8]. Tobacco plants are highly susceptible to the accumulation of bioavailable elements such as cadmium (Cd), lead (Pb), and zinc (Zn) through preferential uptake mechanisms whereby the presence of one mobile element within the soil will stimulate the uptake of others [7], [9]. Levels of these bioactive elements decrease in the following order throughout the tobacco plant: roots > leaves > fruits > seeds [10]. The interaction of Cd2+ and Pb2+ with sulphur⿿hydrogen bonded groups inactivating enzymes to disturb the metabolic process within the cell [7], [10]. Unlike organic materials found in soil, inorganic impurities are not usually removed from a source by chemical or microbial degradation [11], [12]. Elemental fingerprints are typically detected using inductively coupled plasma mass spectrometry (ICP-MS), however, this technique is not practical for rapid on scene diagnostics that are required by U.K. Trading Standards and HMRC due to time constraints and the need for aggressive digestion methods that destroy evidence vital for criminal convictions [8], [13]. X-ray fluorescence (XRF) has previously been scaled down and applied for safe handheld use as an economical and sensitive technique to provide a bulk elemental profiles of plant foliage in under 15 s, easily translatable to tobacco analysis [14], [15], [16].

In some cases, especially to the untrained eye, it is extremely difficult to distinguish visually between licit and counterfeit tobaccos. However, examinations conducted by experienced officers and knowledge of illicit packaging trends at seizure allows for a subjective decision to be made with regards prosecution charges against criminals [17]. A rapid, simple, spectroscopic method of tobacco analysis has the potential to establish a platform for highly discriminative identification of provenance. Due to the complex chemical mixtures found within plant foliage, it is not currently possible to definitively isolate a single absorption band and attribute it to a specific plant constituent, such as chlorophyll, when comparing different types of tobacco [18]. New advances in Fourier transform infrared spectroscopy (FTIR) that have led to improved detection limits and resolution allows for the determination of minor changes in the alkaloid fractions of tobacco, a method which has been adopted by the tobacco quality control industry for the identification of tobacco disease within plants during the incubation period [19].

This research highlights ⿿user-friendly⿿ rapid methods of tobacco provenance determination in an effort to reduce current costly protocols and potential conflicts of interest with regards current costly outsourced laboratory tobacco analysis using ICP-MS, gas chromatography ⿿ mass spectrometry and isotope ratio ⿿ mass spectrometry (IR-MS). This research also offers insights into techniques that do not require the destruction of evidential samples by extraction and digestion. By focusing on differentiation between whole spectra, rather than the specific absorbance⿿s of target alkaloids, this research utilizes a simple analytical technique in tandem with multivariate data analysis to highlight tell-tale fingerprint regions that identify tobacco sample provenance.

Section snippets

Samples

Samples of varying provenance (79 in total) were donated by Lancashire Trading Standards or purchased from a variety of licit retailers across the U.K., France, Spain, Belgium, Germany and Sweden. All samples donated by Lancashire Trading Standards were not utilised as evidence in active cases and were the maximum number of samples made available to the researchers throughout the duration of this study. The samples included illicit, duty free, and niche tobacco and were organised into

Elemental profiling

Calibrated quantitative analysis of XRF spectra is demanding for even the most competent of users thus spectra was qualitatively analysed to reduce data processing times as well as being easier to translate to potential end-users. Elements typically associated with soil attributions such as K, Ca, Mn, Fe, Ni, Cu, Br and Sr were observed within all spectra and peaks were assigned within each spectrum based on the K-line energy transitions only. Compton scatter, sum peaks and escape peaks

Conclusions

Although detection limits currently are no match for established analytical laboratory techniques, such as ICP-MS and IR-MS, this research establishes a platform for the spectroscopic determination of differences between different types of tobacco. Utilizing FTIR and XRF as rapid analytical methods of provenance identification provides the potential to develop a spectral library of tobaccos to aid rapid identification of unknown samples. The observation of palladium within EDX spectra sees the

Acknowledgements

The authors thank Lancashire trading standards for the supply of the variety of samples essential for this research. In addition, the authors acknowledge Dr. Jennifer Readman, Mr. Reece Hall and Mr. James Donnely (University of Central Lancashire, United Kingdom) for their assistance with the experiments.

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