27
Figure 2: Example chromatogram of the herbal based liquor by DHS
phases [2, 3]. The low sample volume used in DHS increases the sensitivity of analytes. This phenomenon may seem counterintuitive, however, this is possible by DHS as the technique effectively enriches most of the analytes.
Twister Stir Bar Sorptive Extraction (SBSE) and Headspace Solid Phase Microextraction (Headspace SPME) are techniques also available to enrich analytes of interest. Twister SBSE is a technique used to enrich analytes onto a magnetic stirrer bar. The most common Twister is coated with a polydimethylsiloxane (PDMS) phase. The Twister bar can be either submerged in an aqueous sample, or can be suspended in the headspace. For the purposes of this article, the Twister is submerged in aqueous samples. The aqueous samples are then placed onto a stirrer plate and stirred for a period of time. Each Twister bar should then be dried with tissue. The enriched analytes are subsequently desorbed in the GC inlet. With Headspace SPME, an SPME fibre is introduced into the headspace and analytes partition into the coating on the fibre. After a fixed time, the fibre is removed and desorbed in the GC inlet. A wide range of fibre coatings are available and this can enable selective extraction of target analytes.
Method
The first series of experiments was designed to determine the differences between the different sampling techniques. A herbal based liquor was chromatographed using Static Headspace analysis, Headspace SPME, Twister SBSE, and DHS using the same GC temperature program and MS conditions. 100 µl of the herbal based liquor was used
Table 1 Instrumentation and method conditions
for DHS, SPME, and Twister SBSE; 2 ml of the herbal based liquor was used for Static Headspace; 5-6 replicates were performed to gain understanding of precision using each technique. Estragole and Anethole were also quantified in the herbal based liquor by DHS.
Finally, the three different orange juices were chromatographed using the same DHS method as for the herbal based liquor to identify if differences could be determined between the different sources of juice. 50 µl of each orange juice was used for DHS; six replicates were performed on orange juice A; individual injections of oranges juices B and C were performed. Table 1 shows the
method conditions used for the analysis. Results and Discussion
Figure 2 shows an example chromatogram of the herbal based liquor by DHS. Several of the volatile ingredients can be observed by DHS. Only Limonene and Anethole were detected by Static Headspace analysis. Over a 100 fold increase in sensitivity was observed for Anethole using DHS when compared to the Static Headspace analysis for the herbal based liquor. Table 2 shows precision obtained for a number of analytes by DHS, Twister SBSE and Headspace SPME. For DHS, the percentage relative standard deviation (% RSD) for Limonene and Eugenol
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
