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Author's personal copy 5532 A. Robbat Jr. et al. / J. Chromatogr. A 1218 (2011) 5531– 5541 concentration, high sensory organics that contribute to avor and aroma. By automating the GC–GC/MS process, portions of the sam- ple from pre-determined time intervals are injected from the rst column onto the second column. In contrast to studies that transfer multiple heartcuts onto the second column, we chose to separate only one portion of the sample per injection. Subsequent injections are made only after the preceding heartcut has completely eluted from the second column. Automated sequential, multidimensional GC/MS offers higher resolution over other separation choices but it is time-consuming, since total analysis time is a function of the number of heartcuts and cumulative GC runtimes: T (min) = x n = 1 [( n t heartcut ) t 1 ] t 2 where n is the rst heartcut, t heartcut is the time-period, t 1 and t 2 are the rst and second column GC runtimes, and x is the total number of heartcuts dened by t 1 / t cut . Automated sequential GC–GC/MS offers the best opportunity for obtaining a pure mass spectrum for each compound in the sample. It is not our intention to compare different multidimensional techniques in this paper; for that see historical [12,13] and updated reviews [14–22] . Previously, we separated a mixture of several essential oils used to make gin by GC–GC/MS to determine if it was possible to detect an adulterant using spectral deconvolution software [23] . Although the mixture contained 101 compounds based on the experimental conditions employed, the goal was not to produce comprehen- sive matrix-specic libraries. Nonetheless, spectral deconvolution of the data correctly identied 23 compounds unique to nutmeg oil, which suggested it might be possible to track an essential oil through the gin distillation process. In this study, we used spectral deconvolution software to iden- tify essential oil compounds when GC–GC/MS could not produce pure spectra during the library-building process and when oil com- ponents were tracked from raw material to nal product by GC/MS. The model mixture selected to study was juniper berry because it is the main ingredient in gin and is added to grain spirit as a botan- ical, oil, or both. In addition to gin, juniper berry is used to avor tea, beer, brandy and marinades for meat, poultry and sh. Estab- lishing the chemical signature of juniper berry is difcult, since its chemical content is dependent on which of the six edible plant species the oil is made from [24,25] as well as the geographic grow- ing environment, age, size, ripeness, and isolation method [26,27] . Other plant materials that become part of the isolation process will also contribute to chemical content [28–30] . The objective of this research is to address the following two questions. Is it possible to identify every detectable compound in juniper berry oil found by GC–GC/MS by GC/MS? Is it possible to track juniper berry content through the manufacturing process and differentiate one gin from another based on the gin’s juniper berry signature? No methods exist to accomplish these tasks. 2. Experimental 2.1. Juniper berry oil samples Juniper berry oils from the same manufacturer but differ- ent batch lots were refrigerated and analyzed as received by GC–GC/MS. A sensory expert examined each sample prior to anal- ysis to determine their usability to make gin. 2.2. Distillate and gin samples Prior to distillation, both the oil and berries were soaked in ethanol for two hrs and tested by a sensory expert for manufac- turing acceptability. The oil mixture contained 47 L oil, 493 mL Table 1 GC–GC/MS columns, temperature and pressure programs. Gas chromatograph Injector and oven temperatures 240 ◦ C 2 L splitless injection Cryotrap/thermal desorption unit (freeze trap − 150 ◦ C, ramp 25 ◦ C/s to 240 ◦ C (10 min)) Column 1 – Rtx-Wax (polyethylene glycol), 30 m × 0.25 mm I.D., 25 m lm thickness Pre-heartcut Initial temp 60 ◦ C (2 min), ramp 4 ◦ C/min to 220 ◦ C (10 min) Initial pressure 31.37 psi (2 min), ramp 0.45 psi/min to 49.45 psi (10 min) Nominal initial helium ow rate 0.7 mL/min, Post-heartcut Initial temp 220 ◦ C, ramp 80 ◦ C/min to 60 ◦ C (2 min), then 3 ◦ C/min to 220 ◦ C (10 min) Initial pressure 49.45 psi, ramp 8.92 psi/min to 31.37 psi (2 min), then ramp 0.33 psi/min to 49.45 psi (10 min) Average velocity 29 cm sec Column 2 – Rxi-5MS (95% dimethyl/5% diphenyl polysiloxane), 30 m × 0.25 mm I.D. column, 25 m lm thickness Pre-heartcut Initial temp 60 ◦ C (2 min), ramp 4 ◦ C/min to 220 ◦ C (10 min) Initial pressure 26.10 psi (2 min), ramp 0.38 psi/min to 41.60 psi (10 min) Helium initial ow 1.5 mL/min Post-heartcut Initial temp 220 ◦ C, ramp 80 ◦ C/min to 60 ◦ C (2 min), then 3 ◦ C/min to 240 ◦ C (10 min) Initial pressure 41.60 psi, ramp 7.60 psi/min to 26.10 psi (2 min), then ramp 0.29 psi/min to 43.90 psi (10 min) Average velocity 49 cm/s Mass spectrometer Solvent delay 50 min Heated transfer line 280 ◦ C Source 230 ◦ C and quadrupole 150 ◦ C temperatures Scan range 30–350 m / z at 8 scans/s EM voltage 1952 spirit, and 267 mL water. Berries (18.4 g) were soaked overnight in 493 mL spirit and 267 mL water. The distillates contained 666 mL of nal product. The analysis of four gins produced by the same manu- facturer over a two-year period produced manufacturing precision data. The analysis of gins obtained from four different manufac- turers produced the data to address the question of whether it is possible to differentiate one manufacturer’s gin from another based on juniper berry content. In these experiments phenanthrene-d10 served as the internal standard (Mix #31006 from Restek Corpora- tion, Bellefonte, PA, USA). All samples were analyzed by GC/MS. 2.3. Juniper berry oil analysis Table 1 lists the columns and instrument operating conditions for the GC–GC/MS work. Agilent (Little Falls, DE, USA) models 6890N/5975C GC/MS were used with a Gerstel (Mülheim an der Ruhr, Germany) MPS 2 autosampler. The GC door was modied to house two low thermal mass column heaters. The columns, wrapped with heater and sensor wires and resistively heated by a separate control module, were connected to one another by a Dean’s switch located inside the GC. The oven was held at 240 ◦ C to heat the transfer lines that connected the injector to the rst column, the rst column to the Dean’s switch, the Dean’s switch to the second column or the ame ionization detector, as well as the second column to the MS. A Gerstel cryotrap/thermal desorber unit was used to condense the sample cut by the Dean’s switch. Also shown in the table are the operating conditions for the GC–GC/MS analysis. To obtain precise heartcuts, both columns followed the same temperature program, which ensured the pres- sures inside the columns were balanced. A 50-min solvent delay was employed so that the MS started with injection of the sample onto the second column. The total runtime for each heartcut was 130 min, which included the time to rinse the syringe prior to injec-
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