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Fast determination of Ziziphora tenuior L. essential oil by inorganic–organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica ab
c
ab
Marzieh Piryaei , Mir Mahdi Abolghasemi & Hossein Nazemiyeh a
Click for updates
Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Sciences, Tabriz, Iran b
Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran c
Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran Published online: 15 Dec 2014.
To cite this article: Marzieh Piryaei, Mir Mahdi Abolghasemi & Hossein Nazemiyeh (2014): Fast determination of Ziziphora tenuior L. essential oil by inorganic–organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica, Natural Product Research: Formerly Natural Product Letters, DOI: 10.1080/14786419.2014.989394 To link to this article: http://dx.doi.org/10.1080/14786419.2014.989394
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Natural Product Research, 2014 http://dx.doi.org/10.1080/14786419.2014.989394
Fast determination of Ziziphora tenuior L. essential oil by inorganic – organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica Downloaded by [Mount Allison University 0Libraries] at 01:35 16 December 2014
Marzieh Piryaeiab, Mir Mahdi Abolghasemic and Hossein Nazemiyehab* a Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Sciences, Tabriz, Iran; bFaculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran; cDepartment of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran
(Received 25 October 2014; final version received 11 November 2014)
In this paper, for the first time, an inorganic– organic hybrid material based on ZnO nanoparticles was anchored to a composite made from polythiophene and hexagonally ordered silica (ZnO/PT/SBA-15) for use in solid-phase fibre microextraction (SPME) of medicinal plants. A homemade SPME apparatus was used for the extraction of volatile components of Ziziphora tenuior L. A simplex method was used for optimisation of five different parameters affecting the efficiency of the extraction. The main constituents extracted by ZnO/PT/SBA-15 and PDMS fibres and hydrodistillation (HD) methods, respectively, included pulegone (51.25%, 53.64% and 56.68%), limonene (6.73%, 6.58% and 8.3%), caryophyllene oxide (5.33%, 4.31% and 4.53%) and 1,8-cineole (4.21%, 3.31% and 3.18%). In comparison with the HD method, the proposed technique could equally monitor almost all the components of the sample, in an easier way, in a shorter time and requiring a much lower amount of the sample. Keywords: ZnO/PT/SBA-15; nanoparticles; solid phase microextraction; Ziziphora tenuior L.
1. Introduction In the last few years, many advances have been made in conventional sample preparation procedures in analytical fields, especially for environmental and biological analyses. Solvent-free extraction methods based on the partitioning of analytes between a gaseous or liquid phase and a stationary phase have become increasingly important and widely applied in research during the last decade. Solid-phase microextraction (SPME) is a new solvent-free extraction method first introduced by Arthur and Pawliszyn (1990) and Lou et al. (2008). The SPME technique uses a polymer-coated
*Corresponding author. Email: [email protected] q 2014 Taylor & Francis
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M. Piryaei et al.
microfibre to concentrate organic analytes from sample phases. SPME has become a common analytical tool, as it allows sensitive analysis, reduced matrix interference, minimal solvent use and full automation of the analytical procedure. In addition, because the fibre typically extracts only a small amount of analytes from the sample, the SPME technique can be used to measure the freely dissolved concentration (equivalent to the fugacity or the activity, depending on the reference phase chosen) of analytes in different matrices. This particular feature renders SPME extremely useful for various environmental and (eco) toxicological investigations (Endo et al. 2011). Many recent researches on SPME have been focused on the preparation and characterisation of new sorbents with remarkable chemical and mechanical stability, enhanced sensitivity and selectivity for specified analytes. Also new materials such as organic–inorganic nanocomposite and nanomaterials materials were synthesised and used as fibre coatings (Gholivand, Abolghasemi, et al. 2011; Hashemi et al. 2012; Sarafraz-Yazdi et al. 2012). ZnO nanomaterials have attracted much attention due to their importance in basic scientific research and their potential in manufacturing nanodevices (Hu et al. 1999; Kind et al. 2002). Up to now, many nanodevices using ZnO nanostructures have been reported including nanolasers (Huang et al. 2001), solar cells (Law et al. 2005), ultraviolet photodetectors (Arnold et al. 2003), gas sensors (Wan et al. 2004), light-emitting diodes (Jeong et al. 2006), field-emission devices (Xu et al. 2004) and so on. Among the applications, gas sensors are different from the others. Gas sensors are based on good gas adsorption properties caused by the high surface-to-volume ratio of ZnO nanostructures. As gas adsorption materials, their application will not stop at gas sensors. But, a few applications except gas sensors based on the gas adsorption properties of ZnO nanostructures have been reported (Abolghasemi et al. 2014). In this paper, inorganic –organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica is synthesised and used, for the first time, as fibre coating of SPME onto stainless steel wires for fast determination volatile compounds of Ziziphora tenuior. The Labiatae is a large family and its aromatic species are used for a variety of purposes such as culinary and folk medicines (Marin et al. 2006). The genus Ziziphora L. belongs to Labiatae family comprising 15 species and subspecies in Iran. Z. tenuior L. is one of these genus members that widely distributed in the country (Rechinger 1982). Ziziphora species were used as culinary herb in Iran. In Iranian folk medicine. Z. tenuior (named as Kakoti in Persian) were used in the treatment of fever, dysentery and uterus infection (Talebi et al. 2012). Using ZnO/PT/SBA-15-SPME followed by GC – MS, 24 compounds were separated and identified in Z. tenuior L., which confirmed the obtained results of hydrodistillation (HD) method. Compared with HD, ZnO/PT/SBA-15-SPME provides the advantages such as a small sample size, timesaving, simplicity and cheapness. 2. Results and discussion 2.1. Optimisation To evaluate the ability of prepared ZnO/PT/SBA-15 nanocomposite for extracting aromatic compounds from Z. tenuir was used. Mesoporous silica SBA-15 is an inorganic material, which does not have good interaction with non-polar organic compounds. Therefore, the use of nanostructure silica for the extraction of volatile organic compounds is rather inconsiderable. To overcome this problem, the polymerisation of SBA-15 with polythiophene was performed to modify the surface of the SBA-15 particles. Because polythiophene contains a conjugated p structure, there is an expectation that it efficiently extracts aromatic compounds easily through p – p and hydrophobic interactions. In addition, the channels in the PT/SBA-15 nanocomposite have sufficient space. Therefore, ZnO nanoparticles that have good gas adsorption properties anchored to the pore walls of the PT/SBA-15 nanocomposite and the ZnO/PT/SBA-15 nanocomposite were successfully prepared (Zhang et al. 2010; Abolghasemi et al. 2014). Isolation, extraction and concentration of the volatile components were performed in one single step with this fibre.
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The extraction temperature, extraction time, temperature desorption, time desorption and sample mass that affect the extraction efficiency of headspace solid-phase microextraction (HSSPME) were studied. A simplex method was used for selection of the optimal extraction conditions in the HS-SPME method. Use of a simplex method can significantly reduce the number of experiments required for the achievement of maximum extraction efficiency. The relative areas of five main peaks in the GC –MS chromatogram (camphene, sabinene, limonene, 1,8-cineole and caryophyllene oxide) were monitored during optimisation. In the simplex method, (n þ 1) initial experiments were designed (n is the number of effective parameters on extraction efficiency in HS-SPME method), the conditions corresponding to the worst response were reflected, and the reflection process was repeated until no further improvement in the response was observed. Some of the reflections were modified when appropriate. The conditions used for the initial experiments and the subsequently designed experiments for HS-SPME are summarised in Table 1. The experimental conditions were obtained by use of a modified reflection method. The modifications were usually performed in accordance with practical limitations of some factors. The results clearly indicate the positive effects of extraction temperature, extraction time, temperature desorption, time desorption and sample mass on the extraction efficiency of HS-SPME methods (Hashemi et al. 2012). As shown in Figure S1, the maximum response was obtained for experiment no. 11. On the basis of these experimental observations, the optimum sample weight was chosen to be 4 g. In the HS-SPME method, the amount of extracted analyte is expected to increase with an increase in the fibre extraction time in the headspace of the sample until 35 min. After this time, the rate of extraction is constant. Table 1 showed that the best results were obtained for an extraction time of 35 min. In addition, the maximum relative peak area of volatile compounds was obtained at 708C. At this temperature, the heating system was capable of evaporating the volatile oil compounds from the herb. Therefore, the HS-SPME extraction required only about 4 g of the sample and was performed in about 35 min. Temperature desorption and desorption time were at 2508C and 3 min, respectively, by GC/MS (Table 1).
2.2. Effect of humidity Because of the ZnO/PT/SBA-15 structure, water vapour (humidity) may affect the fibre ability to adsorb the volatile compounds of Z. tenuir. Therefore, the effect of humidity was studied by the Table 1. Experimental conditions used and results obtained for the HS-SPME experiments performed in the simplex optimisation procedure. Experiment number 1 2 3 4 5 6 7 (reflection) 8 (reflection) 9 (reflection) 10 (reflection) 11 (reflection) 12 (reflection) 13 (reflection)
Extraction temperature (8C)
Sample mass (g)
Extraction time (min)
Temperature desorption (8C)
Time desorption (min)
50 70 50 50 50 50 60 65 70 75 70 90 70
4 4 2 4 4 4 6 5 5.5 6 4 6 4
15 15 15 30 15 15 20 25 30 35 35 25 40
250 250 250 250 260 250 260 260 250 260 250 260 250
3 3 3 3 3 2 2.5 2.5 2 3 3 2.5 3
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Table 2. Constituents of the oil of Z. tenuior L. No
Compounds
RIa
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
a-Pinene Camphene Sabinene b-Pinene Limonene 1,8-Cineole Terpinolene 2-Nonanol Cis-limonene oxide Linalool (dihydro) Trans-limonene oxide Cis beta terpineol Benzyl acetate Neo iso isopulegol a-Terpineol n-Dodecane Pulegone Thymol a-Copaene b-Bourbonene Ethyl decanoate Caryophyllene (Z) Dodecanal E-caryophyllene b-Humulene Caryophyllene alcohol Caryophyllene oxide 1-Hexadecene
938 953 976 979 1032 1034 1088 1096 1134 1135 1139 1145 1163 1168 1189 1199 1237 1290 1376 1384 1395 1404 1408 1418 1440 1568 1581 1593
HD area SPME area Repeatability Reproducibility PDMS area (%)b (%)c RSD (%)d RSD (%) (%)e 1.31 2.1 2.52 0.25 8.30 3.18 1.42 0.09 1.08 0.22 0.37 0.15 1.73 0.84 1.38 0.03 56.68 3.08 0.11 0.27 0.03 0.52 0.08 0.32 1.84 0.32 5.33 1.46
1.24 2.72 2.74 0.18 6.73 4.21 1.28 1.10 0.81 0.12 0.34 0.08 1.03 0.05 1.24 0 51.25 2.47 0.07 0.12 0 0 0 0.26 1.15 0.24 4.31 1.12
3.7 5.5 9.4 3.4 10.5 6.8 4.3 7.1 5.4 3.6 3.7 6.1 8.3 4.9 3.5 2.7 10.1 6.8 4.5 3.1 5.7 8.6 4.2 5.7 9.4 8.5 10.2 7.6
6.3 15.6 6.4 10.3 13.4 18.8 13.2 10.7 13.6 14.3 8.4 12.4 15.6 11.2 12.8 9.7 15.1 16.8 12.5 10.1 8.1 6.3 7.1 6.2 11.3 9.4 16.5 14.7
1.25 1.78 1.32 0.31 6.58 3.31 1.52 0.83 0.52 0.14 0.43 0 0.56 0.10 1.25 0.06 53.64 2.87 0 0.21 0 0.09 0.05 0.21 1.34 0.15 4.53 1.32
a
Retention indexes using a HP-5MS column. Relative area (peak area relative to total peak area) for hydrodistillation method. c Relative area (peak area relative to total peak area) for ZnO/PT/SBA-15-SPME method. d Relative standard deviation (RSD) values for SPME method (n ¼ 4). e Relative area (peak area relative to total peak area) for PDMS-SPME method. b
addition of different amounts of water to the samples in the optimised conditions. The results are shown in Figure S2 for the five target compounds. From these results, it can be concluded that the presence of water vapour in the headspace atmosphere decreases the total and individual peak areas that confirmed the previous reports (Djozan et al. 2001; Gholivand, Piryaei, et al. 2011). It means that the water molecules can deactivate the fibre surface by blocking the active sites; therefore, the proposed fibre is a good adsorptive fibre for sampling from the dried samples (Table 2). 3. Conclusion In this study, the efficiency of ZnO/PT/SBA-15 nanocomposite as a fibre for HS-SPME of volatile compounds in a medicinal plant was investigated for the first time. The proposed method is environmental-friendly because no toxic solvent is used, and thus there is no solvent peak in the chromatogram. The presented experimental results clearly demonstrate that the prepared fibres are suitable for HS-SPME analyses of volatile oils of medicinal plant. Supplementary material Experimental details relating to this article are available online, alongside Figures S1 and S2.
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References Abolghasemi MM, Yousefi V, Hazizadeh B. 2014. An inorganic–organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica for use in solid-phase fiber microextraction of PAHs. Microchim Acta. 181:639– 645. Arnold MS, Avouris P, Pan ZW, Wang ZL. 2003. Field-effect transistors based on single semiconducting oxide nanobelts. J Phys Chem B. 107:659– 663. Arthur CL, Pawliszyn J. 1990. Direct-immerson and headspace mode. Anal Chem. 62:2145–2148. Djozan Dj, Assadi Y, Haddadi SH. 2001. Anodized aluminum wire as a solid-phase microextraction fiber. Anal Chem. 73:4054–4058. Endo S, Droge STJ, Goss KU. 2011. Polyparameter linear free energy models for polyacrylate fiber-water partition coefficients to evaluate the efficiency of solid-phase microextraction. Anal Chem. 83:1394–1400. Gholivand MB, Abolghasemi MM, Fattahpour P. 2011. Polypyrrole/hexagonally ordered silica nanocomposite as a novel fiber coating for solid-phase microextraction. Anal Chem Acta. 704:174–179. Gholivand MB, Piryaei M, Abolghasemi MM. 2011. Anodized aluminum wire as a solid-phase microextraction fiber for rapid determination of volatile constituents in medicinal plant. Anal Chim Acta. 701:1–5. Hashemi P, Badiei A, Shamizadeh M, Mohammadi Ziarani G, Ghiasvand AR. 2012. Preparation of a new solid-phase microextraction fiber by coating silylated nanoporous silica on a copper wire. J Chin Chem Soc. 59:727– 732. Hu J, Odom TW, Lieber CM. 1999. Chemistry and physics in one dimension: synthesis and properties of nanowires and nanotubes. Acc Chem Res. 32:435– 445. Huang MH, Mao S, Feick H, Yan H, Wu Y, Kind H, Weber E, Russo R, Yang P. 2001. Room-temperature ultraviolet nanowire nanolasers. Science. 292:1897–1899. Jeong MC, Oh BY, Ham MH, Myoung JM. 2006. Electroluminescence from ZnO nanowires in n-ZnO film/ZnO nanowire array/p-GaN film heterojunction light-emitting diodes. Appl Phys Lett. 88:202105–202107. Kind H, Yan H, Messer B, Law M, Yang P. 2002. Nanowire ultraviolet photodetectors and optical switches. Adv Mater. 14:158–160. Law M, Greene LE, Johnson JC, Saykally R, Yang P. 2005. Nanowire dye-sensitized solar cells. Nat Mater. 4:445–449. Lou DW, Lee X, Pawliszyn J. 2008. Extraction of formic and acetic acids from aqueous solution by dynamic headspaceneedle trap extraction temperature and pH optimization. J Chromatogr A. 1201:228 –234. Marin M, Koko V, Duletic´-Lausˇevic´ S. 2006. Glandular trichomes on the leaves of Rosmarinus officinalis: morphology, stereology and histochemistry. South Afr J Bot. 72:378–382. Rechinger KH. 1982. Flora Iranica (Labiatae, no. 150). Austria: Akademische Druch-u., Verlagsanstat. Sarafraz-Yazdi A, Ghaemi F, Amiri A. 2012. Comparative study of the sol– gel based solid phase microextraction fibers in extraction of naphthalene, fluorene, anthracene and phenanthrene from saffron samples extractants. Microchim Acta. 176:317–325. Talebi SM, Rezakhanlou A, Salahi Isfahani G. 2012. Trichomes plasticity in Ziziphora tenuior L. (Labiatae) in Iran: an ecological review. Ann Biol Res. 3:668– 672. Wan Q, Li QH, Chen YJ, Wang TH, He XL, Li JP, Lin CL. 2004. Fabrication and ethanol sensing characteristics of ZnO nanowire gas sensors. Appl Phys Lett. 84:3654–3656. Xu CX, Sun XW, Chen BJ. 2004. Field emission from galliumdoped zinc oxide nanofiber array. Appl Phys Lett. 84:1540–1542. Zhang B, Chen X, Ma S, Chen Y, Yang J, Zhang M. 2010. The enhancement of photoresponse of an ordered inorganic– organic hybrid architecture by increasing interfacial contacts. Nanotechnology. 21:065304 –065336.
Natural Product Research: Formerly Natural Product Letters Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gnpl20
Fast determination of Ziziphora tenuior L. essential oil by inorganic–organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica ab
c
ab
Marzieh Piryaei , Mir Mahdi Abolghasemi & Hossein Nazemiyeh a
Click for updates
Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Sciences, Tabriz, Iran b
Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran c
Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran Published online: 15 Dec 2014.
To cite this article: Marzieh Piryaei, Mir Mahdi Abolghasemi & Hossein Nazemiyeh (2014): Fast determination of Ziziphora tenuior L. essential oil by inorganic–organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica, Natural Product Research: Formerly Natural Product Letters, DOI: 10.1080/14786419.2014.989394 To link to this article: http://dx.doi.org/10.1080/14786419.2014.989394
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
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Natural Product Research, 2014 http://dx.doi.org/10.1080/14786419.2014.989394
Fast determination of Ziziphora tenuior L. essential oil by inorganic – organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica Downloaded by [Mount Allison University 0Libraries] at 01:35 16 December 2014
Marzieh Piryaeiab, Mir Mahdi Abolghasemic and Hossein Nazemiyehab* a Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Sciences, Tabriz, Iran; bFaculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran; cDepartment of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran
(Received 25 October 2014; final version received 11 November 2014)
In this paper, for the first time, an inorganic– organic hybrid material based on ZnO nanoparticles was anchored to a composite made from polythiophene and hexagonally ordered silica (ZnO/PT/SBA-15) for use in solid-phase fibre microextraction (SPME) of medicinal plants. A homemade SPME apparatus was used for the extraction of volatile components of Ziziphora tenuior L. A simplex method was used for optimisation of five different parameters affecting the efficiency of the extraction. The main constituents extracted by ZnO/PT/SBA-15 and PDMS fibres and hydrodistillation (HD) methods, respectively, included pulegone (51.25%, 53.64% and 56.68%), limonene (6.73%, 6.58% and 8.3%), caryophyllene oxide (5.33%, 4.31% and 4.53%) and 1,8-cineole (4.21%, 3.31% and 3.18%). In comparison with the HD method, the proposed technique could equally monitor almost all the components of the sample, in an easier way, in a shorter time and requiring a much lower amount of the sample. Keywords: ZnO/PT/SBA-15; nanoparticles; solid phase microextraction; Ziziphora tenuior L.
1. Introduction In the last few years, many advances have been made in conventional sample preparation procedures in analytical fields, especially for environmental and biological analyses. Solvent-free extraction methods based on the partitioning of analytes between a gaseous or liquid phase and a stationary phase have become increasingly important and widely applied in research during the last decade. Solid-phase microextraction (SPME) is a new solvent-free extraction method first introduced by Arthur and Pawliszyn (1990) and Lou et al. (2008). The SPME technique uses a polymer-coated
*Corresponding author. Email: [email protected] q 2014 Taylor & Francis
Downloaded by [Mount Allison University 0Libraries] at 01:35 16 December 2014
2
M. Piryaei et al.
microfibre to concentrate organic analytes from sample phases. SPME has become a common analytical tool, as it allows sensitive analysis, reduced matrix interference, minimal solvent use and full automation of the analytical procedure. In addition, because the fibre typically extracts only a small amount of analytes from the sample, the SPME technique can be used to measure the freely dissolved concentration (equivalent to the fugacity or the activity, depending on the reference phase chosen) of analytes in different matrices. This particular feature renders SPME extremely useful for various environmental and (eco) toxicological investigations (Endo et al. 2011). Many recent researches on SPME have been focused on the preparation and characterisation of new sorbents with remarkable chemical and mechanical stability, enhanced sensitivity and selectivity for specified analytes. Also new materials such as organic–inorganic nanocomposite and nanomaterials materials were synthesised and used as fibre coatings (Gholivand, Abolghasemi, et al. 2011; Hashemi et al. 2012; Sarafraz-Yazdi et al. 2012). ZnO nanomaterials have attracted much attention due to their importance in basic scientific research and their potential in manufacturing nanodevices (Hu et al. 1999; Kind et al. 2002). Up to now, many nanodevices using ZnO nanostructures have been reported including nanolasers (Huang et al. 2001), solar cells (Law et al. 2005), ultraviolet photodetectors (Arnold et al. 2003), gas sensors (Wan et al. 2004), light-emitting diodes (Jeong et al. 2006), field-emission devices (Xu et al. 2004) and so on. Among the applications, gas sensors are different from the others. Gas sensors are based on good gas adsorption properties caused by the high surface-to-volume ratio of ZnO nanostructures. As gas adsorption materials, their application will not stop at gas sensors. But, a few applications except gas sensors based on the gas adsorption properties of ZnO nanostructures have been reported (Abolghasemi et al. 2014). In this paper, inorganic –organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica is synthesised and used, for the first time, as fibre coating of SPME onto stainless steel wires for fast determination volatile compounds of Ziziphora tenuior. The Labiatae is a large family and its aromatic species are used for a variety of purposes such as culinary and folk medicines (Marin et al. 2006). The genus Ziziphora L. belongs to Labiatae family comprising 15 species and subspecies in Iran. Z. tenuior L. is one of these genus members that widely distributed in the country (Rechinger 1982). Ziziphora species were used as culinary herb in Iran. In Iranian folk medicine. Z. tenuior (named as Kakoti in Persian) were used in the treatment of fever, dysentery and uterus infection (Talebi et al. 2012). Using ZnO/PT/SBA-15-SPME followed by GC – MS, 24 compounds were separated and identified in Z. tenuior L., which confirmed the obtained results of hydrodistillation (HD) method. Compared with HD, ZnO/PT/SBA-15-SPME provides the advantages such as a small sample size, timesaving, simplicity and cheapness. 2. Results and discussion 2.1. Optimisation To evaluate the ability of prepared ZnO/PT/SBA-15 nanocomposite for extracting aromatic compounds from Z. tenuir was used. Mesoporous silica SBA-15 is an inorganic material, which does not have good interaction with non-polar organic compounds. Therefore, the use of nanostructure silica for the extraction of volatile organic compounds is rather inconsiderable. To overcome this problem, the polymerisation of SBA-15 with polythiophene was performed to modify the surface of the SBA-15 particles. Because polythiophene contains a conjugated p structure, there is an expectation that it efficiently extracts aromatic compounds easily through p – p and hydrophobic interactions. In addition, the channels in the PT/SBA-15 nanocomposite have sufficient space. Therefore, ZnO nanoparticles that have good gas adsorption properties anchored to the pore walls of the PT/SBA-15 nanocomposite and the ZnO/PT/SBA-15 nanocomposite were successfully prepared (Zhang et al. 2010; Abolghasemi et al. 2014). Isolation, extraction and concentration of the volatile components were performed in one single step with this fibre.
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The extraction temperature, extraction time, temperature desorption, time desorption and sample mass that affect the extraction efficiency of headspace solid-phase microextraction (HSSPME) were studied. A simplex method was used for selection of the optimal extraction conditions in the HS-SPME method. Use of a simplex method can significantly reduce the number of experiments required for the achievement of maximum extraction efficiency. The relative areas of five main peaks in the GC –MS chromatogram (camphene, sabinene, limonene, 1,8-cineole and caryophyllene oxide) were monitored during optimisation. In the simplex method, (n þ 1) initial experiments were designed (n is the number of effective parameters on extraction efficiency in HS-SPME method), the conditions corresponding to the worst response were reflected, and the reflection process was repeated until no further improvement in the response was observed. Some of the reflections were modified when appropriate. The conditions used for the initial experiments and the subsequently designed experiments for HS-SPME are summarised in Table 1. The experimental conditions were obtained by use of a modified reflection method. The modifications were usually performed in accordance with practical limitations of some factors. The results clearly indicate the positive effects of extraction temperature, extraction time, temperature desorption, time desorption and sample mass on the extraction efficiency of HS-SPME methods (Hashemi et al. 2012). As shown in Figure S1, the maximum response was obtained for experiment no. 11. On the basis of these experimental observations, the optimum sample weight was chosen to be 4 g. In the HS-SPME method, the amount of extracted analyte is expected to increase with an increase in the fibre extraction time in the headspace of the sample until 35 min. After this time, the rate of extraction is constant. Table 1 showed that the best results were obtained for an extraction time of 35 min. In addition, the maximum relative peak area of volatile compounds was obtained at 708C. At this temperature, the heating system was capable of evaporating the volatile oil compounds from the herb. Therefore, the HS-SPME extraction required only about 4 g of the sample and was performed in about 35 min. Temperature desorption and desorption time were at 2508C and 3 min, respectively, by GC/MS (Table 1).
2.2. Effect of humidity Because of the ZnO/PT/SBA-15 structure, water vapour (humidity) may affect the fibre ability to adsorb the volatile compounds of Z. tenuir. Therefore, the effect of humidity was studied by the Table 1. Experimental conditions used and results obtained for the HS-SPME experiments performed in the simplex optimisation procedure. Experiment number 1 2 3 4 5 6 7 (reflection) 8 (reflection) 9 (reflection) 10 (reflection) 11 (reflection) 12 (reflection) 13 (reflection)
Extraction temperature (8C)
Sample mass (g)
Extraction time (min)
Temperature desorption (8C)
Time desorption (min)
50 70 50 50 50 50 60 65 70 75 70 90 70
4 4 2 4 4 4 6 5 5.5 6 4 6 4
15 15 15 30 15 15 20 25 30 35 35 25 40
250 250 250 250 260 250 260 260 250 260 250 260 250
3 3 3 3 3 2 2.5 2.5 2 3 3 2.5 3
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Table 2. Constituents of the oil of Z. tenuior L. No
Compounds
RIa
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
a-Pinene Camphene Sabinene b-Pinene Limonene 1,8-Cineole Terpinolene 2-Nonanol Cis-limonene oxide Linalool (dihydro) Trans-limonene oxide Cis beta terpineol Benzyl acetate Neo iso isopulegol a-Terpineol n-Dodecane Pulegone Thymol a-Copaene b-Bourbonene Ethyl decanoate Caryophyllene (Z) Dodecanal E-caryophyllene b-Humulene Caryophyllene alcohol Caryophyllene oxide 1-Hexadecene
938 953 976 979 1032 1034 1088 1096 1134 1135 1139 1145 1163 1168 1189 1199 1237 1290 1376 1384 1395 1404 1408 1418 1440 1568 1581 1593
HD area SPME area Repeatability Reproducibility PDMS area (%)b (%)c RSD (%)d RSD (%) (%)e 1.31 2.1 2.52 0.25 8.30 3.18 1.42 0.09 1.08 0.22 0.37 0.15 1.73 0.84 1.38 0.03 56.68 3.08 0.11 0.27 0.03 0.52 0.08 0.32 1.84 0.32 5.33 1.46
1.24 2.72 2.74 0.18 6.73 4.21 1.28 1.10 0.81 0.12 0.34 0.08 1.03 0.05 1.24 0 51.25 2.47 0.07 0.12 0 0 0 0.26 1.15 0.24 4.31 1.12
3.7 5.5 9.4 3.4 10.5 6.8 4.3 7.1 5.4 3.6 3.7 6.1 8.3 4.9 3.5 2.7 10.1 6.8 4.5 3.1 5.7 8.6 4.2 5.7 9.4 8.5 10.2 7.6
6.3 15.6 6.4 10.3 13.4 18.8 13.2 10.7 13.6 14.3 8.4 12.4 15.6 11.2 12.8 9.7 15.1 16.8 12.5 10.1 8.1 6.3 7.1 6.2 11.3 9.4 16.5 14.7
1.25 1.78 1.32 0.31 6.58 3.31 1.52 0.83 0.52 0.14 0.43 0 0.56 0.10 1.25 0.06 53.64 2.87 0 0.21 0 0.09 0.05 0.21 1.34 0.15 4.53 1.32
a
Retention indexes using a HP-5MS column. Relative area (peak area relative to total peak area) for hydrodistillation method. c Relative area (peak area relative to total peak area) for ZnO/PT/SBA-15-SPME method. d Relative standard deviation (RSD) values for SPME method (n ¼ 4). e Relative area (peak area relative to total peak area) for PDMS-SPME method. b
addition of different amounts of water to the samples in the optimised conditions. The results are shown in Figure S2 for the five target compounds. From these results, it can be concluded that the presence of water vapour in the headspace atmosphere decreases the total and individual peak areas that confirmed the previous reports (Djozan et al. 2001; Gholivand, Piryaei, et al. 2011). It means that the water molecules can deactivate the fibre surface by blocking the active sites; therefore, the proposed fibre is a good adsorptive fibre for sampling from the dried samples (Table 2). 3. Conclusion In this study, the efficiency of ZnO/PT/SBA-15 nanocomposite as a fibre for HS-SPME of volatile compounds in a medicinal plant was investigated for the first time. The proposed method is environmental-friendly because no toxic solvent is used, and thus there is no solvent peak in the chromatogram. The presented experimental results clearly demonstrate that the prepared fibres are suitable for HS-SPME analyses of volatile oils of medicinal plant. Supplementary material Experimental details relating to this article are available online, alongside Figures S1 and S2.
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