Sniff port

Selecting an approach Off-flavors are typically due to volatile compounds present at extremely low levels. (Flavor is sensed more by the olfactory system than the tongue, which senses only 5 flavors, sweet, sour, bitter, salty, and umami). GC is ideal for detecting low levels of volatile components. In this case, headspace GC will allow you to treat the plastic directly. Since the off-flavor is suspected to be derived from the polypropylene packaging material, you decide to compare different samples ( good vs. bad ) of the material using headspace GC with both a flame ionization detector (FID) and a sniff port. These chromatograms are shown in Fig. 21.9. 

Implementation GC-MS in an ion-profiling mode was used to compare the two samples. At the retention time where sniff-port detection noted the off-flavor, differences were observed (Fig. 21.10). A compound with a mass-to-charge ratio (m/z) of 104 (the off-flavor suspect ) is co-eluting with another compound. 

Commentary This problem, like many other off-flavor and off-odor problems, was difficult because the offending compound was present at a very low level and was difficult to separate from another compound present in the sample. The two keys to this problem were the use of the handle (the off-flavor), detected with the sniff port, and the mass... 

Figure G1.8.1 Diagram of the sniff port constructed from a laboratory filter (based on Acree et al., 1976 see Acree, 1997) showing the filter pump (with the check ball removed) attached to a humidifier, shut-off valve, and charcoal filter. The vacuum side of the pump is positioned over a flame ionization detector (FID) with the hydrogen gas turned off. The make-up gas helps lift the narrow (<0.2-mm-o.d.) gas chromatography (GC) effluent stream into the much larger olfactometry air stream without loss of resolution, and the 300 ml/min air combustion gas produced by the FID also prevents loss of resolution.

Sniff port (e.g., DATU, Gerstel, Microanalytics also see Acree et al., 1976) Splitless injector (linear velocity 36 cm/sec or 2 ml/min, detector temperature, 250°C)... 

Position a sniffer so as to provide comfortable access to the sniff port for the duration of the analysis. 

Have the sniffer breathe in constant cycles at 20 breaths/min, record the exact moment an odor is first detected at the sniff port, associate it with a descriptor, and then record the moment the odor is no longer detectable. 

Set up the necessary apparatus for the desired number of sniffers (see Basic Protocol 1, step 1). For a typical setup, split the effluent to two sniff ports and an FID so that two assessors can sniff the effluent simultaneously (without seeing each other). 

Tekar Co., Cincimiati, OH), flame ionization detector, and sniff port. RB-HVP (0.1 g) dissolved in 5 ttiL of odorless-distilled was placed in a 25 mL headspace sanq)ling tube. The san le was preheated to 60°C for S min. Volatiles were purged onto a Tenax TA trap (Tekmar Co.) at 60 C with helium (40 mL/min) for 2.5, 7.5, 22.5 and 67.5 min, which corresponded to purge volumes of 100, 300, 900 and 2700 mL, respectively. All other purge and trap conditions were the same as previously described by Wu and Cadwallader (75). G CO conditions were same as described above for AEDA. A freshly prepared sanq>le was used for each analysis. 

Gas chromatography, (GC) sniffing, aroma extract dilution analysis (AEDA), and CHARM analysis are well accepted tools to identify the sensory properties of individual molecules in complex mixtures [9-10]. In fact, they are the fastest tool to identify typical character impact molecules and odor off-notes. They require well trained people who are able to keep pace with the fast emerging GC peaks imagine that a small gas balloon of ca. 0.1 mL leaving the sniff port within 3 sec has to be transferred to the... 

FES Flame emission spectrometry GC-SNIFF Sniffing port gas chromatography... 

Move the column from the FID port to the olfactometer port and turn on the sniff air flows. 

GC can be safely and routinely used for essential oils of known composition whose constituents already have been elucidated by hyphenated techniques like GC/MS, GC/FT-IR, NMR, and so on. The use of GC alone for the analysis of new or uncommon essential oils is recommended only for reference information leading to tentative identification of the major constituents. This information also requires support by sensory evaluation. Quantitative determination of the separated constiments must be achieved by GC. Odor evaluation of the eluted components from a GC column is possible through the introduction of a sniffing port fixed to the end of the column via an all-glass splitting device. This allows the analyst to sniff the compound eluted while it simultaneously appears as a peak on the integrator/recorder. 

GC-Olfactometry (GC-O) or sniffing describes techniques that use the human nose to detect and evaluate volatile compounds eluting from a GC separation (Delahunty, 2006). Assessors sniff the eluate from a specifically designed odour port parallel to FID or MS detection. GC-O applications have become common not limited to the food and flavour industry to assign specific flavour characteristics to each of the volatile compounds identified. The human nose plays the role of the detector. However, the human nose is often more sensitive than any physical detector, and GC-O exhibits supplementary capabilities that can be applied to any fragrant product. 

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