Determination of the concentration of quaternary ammonium compounds (QAV) in disinfectants.
Suitable for all solutions containing quaternary ammonium compounds (QAV).
Many basic dyes (e.g. methylene blue) behave in a similar way to cation-active substances. Methylene blue forms a complex with dodecyl sulfate (anion-active surfactant), for example, which is soluble in organic solvents such as dichloromethane with blue colour. By adding quaternary ammonium compounds (QAV), this complex is decomposed and the methylene blue migrates from the dichloromethane into the aqueous phase. When titrating quaternary ammonium compounds with dodecyl sulfate, this process takes place in the opposite direction, i.e. the methylene blue migrates from the aqueous to the dichloromethane phase. The end point of the titration is reached when the aqueous and dichloromethane phases have the same colour depth.
Or to put it in other words:
Methylene blue (water-soluble dye in cationic form) forms a complex with dodecyl sulfate (anionic surfactant), which is soluble in organic solvents, e.g. dichloromethane, with blue colour. On the other hand, QAV also forms a complex with dodecyl sulfate, so that the indicator migrates into the organic phase once the equivalence point has been exceeded.
Malt intended for use in beer brewing or elsewhere in the food industry
Applicable for all (laboratory) worts
The Congress wort is heated in order to inactivate the amylolytic enzymes, and afterwards, yeast is added and the wort is allowed to completely ferment out at a minimum temperature of 20 °C in a fermentation tube (fig. 1). The difference in the extract before and after fermentation is measured in order to calculate the limit of attenuation.
Applicable for all (laboratory) worts
The Congress wort is heated in order to inactivate the amylolytic enzymes. Afterwards, 16 g/100 ml yeast is added, and the wort is allowed to completely ferment out in approx. 7 h.
Determination of the "air volume" (gas volume other than carbon dioxide) and oxygen in the headspace of cylinders and cans
Suitable for determination in beer, mixed beer beverages and carbonated beverages
The burette containing the caustic solution, in this case, is equipped with a short capillary outlet. A tube is attached to this outlet, connecting the burette to a second burette with a lower capillary outlet. The second burette contains an alkaline solution of sodium dithionite, which binds oxygen [1, 2]. In the first burette, the volume of air is measured, and in the second, the volume of nitrogen.
Industrial yeasts from the brewing process.
Live, aerobic yeast cells possess dehydrogeneases which reduce the methylene blue absorbed into the cell to its colourless leuco form, giving the cells a pale blue colour. Dead or inactive cells lack dehydrogenase activity and turn an intense blue colour.