Short-path thermal desorber

Dried vanilla bean sections were subjected to ballistic heating in a short-path thermal desorber, and the volatiles so obtained were analyzed by GC and GC-MS. Over 60 flavor compounds, 18 of them phenolics, were detected by this technique. The method is... 

Figure 1. Diagram of the short path thermal desorber (SPTD) used for...

The short path thermal desorber (SPTD Figure 1) was used to isolate the volatiles from cooked and cooked/stored ground beef. The SPTD was chosen for use as it enabled us to maintain accurate control of the sparge, purge, and desorption temperatures, and to have minimal space between the sample and the capillary colunm. Since metal ions catalyze the process of lipid oxidation 31), use of the SPTD also minimized the amount of metal the sample and volatiles would contact. 

An automated system called the short-path thermal desorber (SPTD) (Fig. 2) was developed jointly by researchers at Rutgers University and Scientific Instrument Services of Ringoes, New Jersey (an independent company, separate from the previously mentioned SIS) (14). This instrument is placed on top of the GC injection port and can be adjusted to allow conventional injections without disconnecting the unit. The sample is placed in a glass-lined stainless steel tube and held in place with glass wool. An injection needle is affixed to one end and the other end is screwed into the SPTD. The injection is made pneumatically, and the sample is not heated prior to injection. Control of the temperature, desorption time, and equilibration are provided by an electronic controlling unit. An automated system has an inherent advantage over manual systems for improved reproducibility from one run to the next. Quantitative data with a precision of less than 5% STD has been reported (15). 

Figure 2 The short-path thermal desorber is here shown in the load position. Following desorption, valve 1 is closed and valve 2 is opened.

FIGURE 16.9 Total-ion chromatogram resulting from volatiles of a 2-mg sample of vegetation (mint) adulterated with phencyclidine (PCP) desorbed directly into the gas chromatographic injection port with a short-path thermal desorption unit at 85°C for 5 min. GCMSD conditions 12-m HP-1 x 0.20-mm-i.d. x 0.33-(xm film —10 to 250°C at 10°C/min injection = 250°C. (Courtesy of New Jersey State Police.)... 

Distillation, as defined in this chapter, also includes direct thermal analysis techniques. These techniques involve the heating of a food sample in an in-line (i.e., in the carrier gas flow of the (jC) desorber. (jenerally, aroma compounds are thermally desorbed from the food and then cryofocused to enhance chromatographic resolution. This technique has been used for a number of years for the analysis of lipids and was later modified to include aqueous samples [32,33]. Aqueous samples were accommodated by including a water trap after the desorption cell. This general approach has been incorporated into the short path thermal desorption apparatus discussed by Hartman et al. [34] and Grimm et al. [35]. A schematic of this apparatus is shown in Figure 3.5. In the schematic shown, a sample of food is placed in the desorption tube and quickly heated. The volatiles are distilled into the gas flow that carries them into the cooled injection system where they are cryofocused prior to injection into the analytical colunm. 

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