Search: O2

Under the influence of oxygen, which is liberated through the degradation of hydrogen peroxide, the barley kernels emerge from dormancy. In this way, germination can be induced at any given time.

Xanthohumol and isoxanthohumol are dissolved with acetonitrile from the sample and following separation, are determined using a Nucleodur C18 column and UV detection.

The total gas pressure in beer is measured after the beer has been forcefully shaken. The carbon dioxide is then bound through the addition of potassium hydroxide. The amount of air in the beer contributes the remaining volume of gas. Once the value for the total pressure has been corrected by subtracting the quantity of air present in the beer, the carbon dioxide can be measured [1].

The bottled or canned beer is brought to 20 °C and mechanically shaken, thereby achieving equilibrium between the oxygen dissolved in the beer and the oxygen present in the headspace (Henry’s and Dalton’s laws). By directly measuring either the oxygen in the beer or in the headspace, the total oxygen can be calculated through referencing a table of values, which includes the headspace volume as a percentage of the fill volume.

The measurement process using a Digox Analyzer works according to the principle of the potentiostatic three-electrode measurement system developed by TÖDT and TESKE and does not require a membrane.

The measuring electrode consists of solid silver, while the counter electrode is made of stainless steel. The reference electrode is composed of silver/silver chloride.

After generating a defined “polarization voltage”, an electrochemical reaction occurs at the measuring electrode, inducing a reduction of the oxygen molecules in the sample.

Measuring electrode (silver):

O₂ + 2 H₂O + 4 e⁻ → 4 OH⁻ (cathodic process)

Counter electrode (stainless steel):

4 OH⁻ → O₂ + 2 H₂O + 4 e⁻ (anodic process)

The flow of current as a result of this reaction is directly proportional to the amount of dissolved oxygen in the sample, if the polarization voltage is fixed as close to the level of the diffusion threshold current as possible.

In this case, the relationship can be represented as follows:

I = K × C_O2, whereupon K = n × F × A × 1/d

I = sensor current

C_O2 = oxygen concentration

F = Faraday constant

n = number of electrons per molecule

A = cathode surface

d = thickness of the “undisturbed layer” along the wall

The thickness of the undisturbed layer along the wall is determined by the hydrodynamic relationships at the measurement electrode and the transportation of oxygen molecules across the boundary layer brought about by temperature-dependent diffusion processes. Both of these clearly defined factors are precisely measured and compensated.

In order to adjust the polarization voltage between the two electrodes, a third electrode, the reference electrode, is employed in Digox measurement devices. This reference electrode remains in contact with the surface of the measuring electrode over a diaphragm in order to prevent mass transfer [1, 2, 3].

Active calibration:

In-line calibration is integrated into the device and is initiated by pressing a button. Taking advantage of Faraday’s Law, an exactly defined amount of oxygen is produced through the electrolysis of water.

I × t = m × F

I = current required for electrolysis

t = time

m = mass, g/mol

F = Faraday constant

The oxygen dissolves in the medium as it flows through and is detected at the measuring cell. The hydrogen liberated during the electrolysis reaction is not relevant for the measurement. The microprocessor monitors the calibration values and carries out any necessary corrective measures. The electrolysis enables the calibration of the device to be carried out under the same conditions and in the same medium as the analysis. Measurement operations are not disrupted during the calibration process [3].

The following applies to Digox 6.1 and all later models: In order to precisely determine the necessary potential for the measurement system, the Digox Analyzer possesses a scanner, which records the product-specific behavior of the medium subject to analysis. This can establish, whether the medium – due to the additives or supplements – must be measured at another potential. In this way, all types of beer-based beverages, non-alcoholic beverages and wine can be analyzed. Moreover, oxygen-reducing substances which can cause the calibration to be inaccurate may also be detected using the calibration scanning process. The device automatically implements the necessary compensative measures with the factors it has determined.