Search: TEA detector

One of the basic prerequisites for properly conducting sensory analysis is selecting suitable candidates as members of the tasting panel.

A (modified) Congress wort is produced from malt samples prior to analysis. NDMA present in the Congress wort is extracted using dichloromethane followed by concentration of the eluate. The determination is performed with a gas chromatograph using a packed Carbowax 20M column with a specific TEA detector (thermal energy analyzer); nitrosodipropylamine (NDPA) serves as an internal standard.

This detector analyzes nitrosamine according to the following procedure:

After exiting the GC column, the separated substances are heated to 500 °C in a pyrolyzer. At this temperature, the N-NO bond of the nitrosamine is broken, thus forming an NO radical (NO۰): 

The gas mixture then flows through a special filter (CTR^TM gas stream filter), which only allows the carrier gas and the NO radicals to pass. After exiting the filter, the NO radicals flow into a reaction chamber along with ozone, which is created by a special generator. The following chemical reactions take place in the chamber: 

These NO radicals react with ozone, forming nitrogen dioxide in an excited state (NO₂•). The NO₂• molecules decompose spontaneously to form nitrogen dioxide in its common form (NO₂), emitting radiation (h•ν) with a wavelength of approx. 600 nm. 

The NDMA is extracted from the wort (plant wort) and beer on Extrelut®, Tox Elut® or comparable material using dichloromethane and the eluate is then concentrated. The determination is carried out by gas chromatography with the specific TEA detector ("Thermal Energy Analyzer"). Nitrosodipropylamine (NDPA) or nitrosodiisopropylamine (NDiPA) is used as the internal standard (ISTD). This detector detects nitrosamines according to the following scheme: After exiting the GC column, the separated substances first enter a pyrolysis oven, where they are heated to around 500 °C. The detector is used as an internal standard (ISTD). At this temperature, the (N-NO) bond of the nitrosamines breaks down, forming an NO radical (NO^-):
 

The gas mixture then passes through a special filter (CTR Gas Stream Filter), which only allows the carrier gas and NO radicals to pass through. The NO radicals and ozone produced by a special generator then flow into a reaction chamber, where the following reaction takes place:

These NO radicals react with ozone to form nitrogen dioxide in an excited state (NO₂^-) and oxygen. The NO2- decomposes spontaneously into ordinary nitrogen dioxide (NO₂) by emitting radiant energy (h-ν) at a wavelength of around 600 nm.

Volatile aroma compounds are driven out of the sample through steam distillation. The ethanol distillate is adjusted to be alkaline and saturated with NaCl. The extraction of the aroma compounds is performed by shaking out with dichloromethane and the phases separated by centrifuging. The organic phase is further concentrated in a stream of nitrogen gas. An ammonia solution is added to remove the acids, because the acids would co-elute, thus preventing quantification of the target substances.

Volatile aroma compounds are driven out of the sample through steam distillation. The ethanolic distillate is saturated with NaCl. Potassium hydrogen sulfite is added to separate carbonyl groups that might interfere with the analysis. The extraction of the aroma compounds is performed by shaking out with dichloromethane and the phases separated by centrifuging.

The phenol fraction collected through steam distillation is mixed with 4-amino- 2,3-dimethyl-1-phenyl-3-pyrazolin-5-one (4-aminophenazone) under alkaline conditions and oxidized by potassium hexacyanoferrate(III) to form a pigment (fig. 1), which after extraction with chloroform, can be measured spectrophotometrically.