Direct, Real-Time Mass Spectrometry Analysis of Cinnamon

To ensure food safety, rapid detection of adulterated and counterfeit food products is critical. One such method, Direct Analysis in Real Time-Mass Spectrometry (DART-MS) (IonSense, Saugus, Mass.), quickly screens and analyzes a wide array of samples for mass spectral information1–3 and does not require sample preparation.

As an example, several recent studies4–8 detail the analysis of cinnamon, mostly using chromatographic methods. High concentrations of coumarin in cinnamon have prompted numerous investigations as well, as its presence is suspected of being harmful.9–11 All of these studies require sample derivatization and long analysis times.

In the current study, DART-MS was used to analyze cinnamon (see Table 1) and detect the presence of coumarin.

Table 1 – Four cinnamon sources

Materials and methods

Instrument and chemicals

The analytical instrument comprised a DART ion source (IonSense) and JMS-T100LC AccuTOF time-of-flight mass spectrometer (JEOL, Peabody, Mass.).12 Standard compounds typically found in cinnamon were analyzed as references (Sigma Aldrich, St. Louis, Mo.): coumarin, cinnamaldehyde (natural), trans-cinnamaldehyde, cinnamic acid (natural), trans-cinnamic acid and eugenol. When necessary, these were diluted with HPLC-grade methanol (Fisher Scientific, Pittsburgh, Penn.). All neat solutions and powders were administered using melting-point capillaries (90 mm, 0.2 mm wall, Fisher Scientific).

Commercial samples

Samples of ground cinnamon and cinnamon bark and sticks (solids) (brand A) and one sample each of ground and sticks (brand B) were tested.

Analysis methods

Standards and their dilutions were analyzed as neat solutions using a capillary dipped in solution and placed in the helium plasma stream. Blank capillaries in solvent were also analyzed for background compounds. All standards in their original concentrations were analyzed in both negative and positive ion modes at temperatures of 100, 150, 200, 250, 350 and 450 °C. These analyses were evaluated for an ion mode and temperature that produced the best response for each compound. Grid voltages were set to 350 °C for negative and positive ion modes for all analyses.

Sample introduction is accomplished by dipping a capillary into a liquid or powder and placing this end in the helium stream, not by administering a known volume. As such, DART-MS used in this manner is not quantitative. This study analyzed successive dilutions of 1:10 in methanol until no analyte was detected for a sense of relative detection limits.

Ground cinnamon samples were analyzed by dipping glass capillaries into the powder and placing the small amount of powder adhered to the capillary in the helium stream. Bark and commercial product samples were sectioned to sample sizes so that they could be gripped with a pair of tweezers and held in the helium stream.

Results

Standard cinnamon compounds

The six standards shown in Table 2 produced the best response using 350 °C plasma in positive ion mode. These conditions were used for all subsequent analyses. Table 2 shows each compound’s exact mass, base mass peak and lowest concentration detected after sequential dilutions in methanol. Additional masses and their most likely corresponding compounds identified in the standard analyses are shown. The responses for the same standard from different sources (i.e., natural and trans-) demonstrated similar results. Coumarin and cinnamaldhydes were detected at 100 μg/L, while the detection of cinnamic acid and eugenol was less sensitive at 10 mg/L.

Table 2 – Standard cinnamon compounds with corresponding base peak and lowest concentration detected at 350 °C, positive ion mode, by DART-MS

Compound identification in cinnamon samples

A list of masses routinely found among the samples was combined with a list of compounds identified in cinnamon analyses by other methods cited in the literature. Table 3 shows these mass peaks and their assignments along with their detection using DART-MS for ground and solid samples. The table highlights the extent to which DART-MS can produce mass data from a single sample, although, with the exception of the standards, these compound assignments are tentative and should be confirmed by another method.

Table 3 – Cinnamon peak summary, sorted by increasing exact mass detected at 350 °C, positive ion mode, by DART-MS

Several compounds have isobars that correspond to compounds found in both plants and cinnamon; Table 4 shows possible isobars. Experiments under identical conditions using standards of all possible compounds would be needed to verify which isobar (or both) is actually present.

Table 4 – Possible isobars in cinnamon samples

Major compounds detected in ground and solid cinnamon samples

The four most intense peaks in each sample form are listed in Table 5. Cinnamaldehyde was the most intense peak in both ground and solid samples. The coumarin peak was next in intensity for all ground samples, except for the Ceylonese samples. Solid samples varied more from sample to sample and among multiple analyses of the same sample than the ground form. As noted earlier, some of the masses could only be identified by their elemental formula, and these are listed with the most likely compound.

Table 5 – Major compounds in ground cinnamon samples in decreasing response (1>2>3>4); compounds in parentheses indicate most likely compound for the mass detected

The results show a fingerprint for the sourced samples, with the major differences between the ground and solid samples being additional plant-based compounds. Eugenol was not detected in high amounts in any of the samples, although it is usually listed as a major component in the literature. Using DART-MS, eugenol and cinnamic acid were detected at similar levels, around 10 mg/L. Several authors cite cinnamic acid as typically being higher in concentration than eugenol in cinnamon samples.4,11 This discrepancy may be attributed to the sensitivity of these compounds using the DART-MS instrument.

Ground samples of the four sourced samples were clearly distinguishable by different coumarin levels, with the Ceylonese cinnamon having the lowest amount. The Indonesian and Vietnamese ground samples showed higher amounts of coumarin than their solid counterparts. Overall, the solid samples were more variable from analysis to analysis, most notably in their coumarin levels. The ground, nonsourced sample of brand A was comparable to a Chinese-sourced ground sample, while brand B was close to both a Chinese-sourced solid sample and Indonesian source solid sample. No coumarin was detected in the brand B solid sample.

Conclusion

DART-MS analysis differentiated commercial samples of ground and solid cinnamon in minutes and easily detected coumarin. No sample preparation or derivatization was required, and samples were analyzed directly from their commercial containers. Further studies are needed to analyze these samples, and standard compounds attributed to species in the mass spectra should be conducted using additional chromatographic methods.

References

  1. Hrbek, V.; Hajslove, J. et al. Ambient mass spectrometry employing direct analysis in real time (DART) ion source for olive oil quality and authenticity assessment. Anal. Chim. Acta 2009, 645(1–2), 56–63.
  2. Kim, H.J. and Jang, P.Y. Identification of ambiguous cubeb fruit by DART-MS-based fingerprinting combined with principal component analysis. Food Chem. 2011, 129(2), 1019–24.
  3. Kpegba, K.; Agbonon, A. et al. Epiafzelechin from the root bark of Cassi sieberiana: detection by DART mass spectrometry, spectroscopic characterization, and antioxidant properties. J. Natural Products 2011, 74(3), 455–9.
  4. Adinew, B. GC-MS and FT-IR analysis of constituents of essential oil from cinnamon bark growing in Southwest of Ethiopia. Int. J. Herbal Med. 2014, 1(6), 22–31.
  5. Ding, Y.; Wu, E.Q. et al. Discrimination of cinnamon bark and cinnamon twig samples sourced from various countries using HPLC-based fingerprint analysis. Food Chem. 2011, 127, 755–60.
  6. Hena, R.; Kumaravel, S. et al. Chromatograph interfaced to a mass spectrometer analysis of Cinnamomun verum. Nature and Science 2010, 8(11), 152–5.
  7. Jayaprakasha, G.K.; Rao, L.J. et al. Chemical composition of volatile oil from Cinnamomum zeylanciaum buds. Verlag der Zeitschrift für Naturforschung 2002, 990–3.
  8. Wen, K.C.; Huang, C.Y. et al. Determination of cinnamic acid and paeoniflorin in traditional Chinese medicinal preparations by high-performance liquid chromatography. J. Chromatogr. 1992, 593, 191–9.
  9. Ballin, N.B.; Sørensen, A.T. Coumarin content cinnamon containing food products on the Danish market. Food Control 2014, 38, 198–203.
  10. Blahová, J. and Svobodová, Z. Assessment of coumarin levels in ground cinnamon available in the Czech retail market. The Scientific World J.2012, 1–4.
  11. Wang, Y.H.; Avula, B. et al. Cassia cinnamon as a source of coumarin in cinnamon-flavored food and food supplements in the United States. J. Agricultural and Food Chem. 2013, 61(18), 4470–6.
  12. Cody, R.B.; Laramee, J.A. et al. Versitile new ion source for the analysis of materials in open air under ambient conditions. Anal. Chem. 2005, 77, 2297–2302.

Joseph R. Swider is senior research scientist at McCrone Associates, 850 Pasquinelli Dr., Westmont, Ill. 60059, U.S.A.; tel.: 630-887-7100; e-mail: [email protected]; www.mccrone.com. Jeffrey A. Jankowski is associate professor of Chemistry, and Antonio Sobevski is student at North Central College, Department of Chemistry, Naperville, Ill.

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