pH-electrodes

The platinum hydrogen electrode is the only electrode whose potential is determined directly by the hydrogen ions activity. The pH-value and the hydrogen potential are directly connected with each other. The potential, depending on the pH-value, can be calculated by means of the Nernst equation.

ph-electrodes
Principle of the platinum hydrogen pH-electrode pHydrunio

Principle of the platinum hydrogen pH-electrode pHydrunio, a combination electrode of two platinum hydrogen electrodes

So, it comes naturally to mind to combine two platinum hydrogen reference electrodes to a combination electrode to create a new platinum hydrogen pH-electrode. That was enabled by the miniaturization of the hydrogen electrode HydroFlex. Two platinum hydrogen electrodes are combined to a pH-electrode. The interior hydrogen electrode is the reference electrode. It must immerse in a buffer of a known pH-value. The ionic connection to the measuring solution is made by a diaphragm. The outer platinum hydrogen electrode is the actual measuring electrode (outer electrode). The voltage is tapped via a voltmeter between the two platinum hydrogen electrodes.

The measuring voltage and the pH-value are related to each other as shown in the following:

Beziehung Messspannung und pH-Wert

The measuring voltage can be converted into the pH-value by adjusting the equation.

E = measured voltage in Volt
R = universal gas constant 8,314 J mol-1 K1
F = Faraday constant 96485 C mol1
T = temperature in Kelvin K
pHinside = 7

Simplified the equation for the converting of the measured voltage E into the pH-value is

download potential table
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pHydrunio – the platinum hydrogen pH-electrode

pHydrunio – Die Platinwasserstoff-pH-Elektrode

Platinum hydrogen pH-electrode pHydrunio

pHydrunio (Patent DE 10 2011 113941) is worldwide the first platinum hydrogen pH-electrode for sale and the logical further development of our mini platinum hydrogen electrode Mini-HydroFlex. It combines a reversible platinum hydrogen electrode as the measuring electrode with a platinum hydrogen reference electrode in an interior electrolyte (pH 7) as the reference electrode. It is delivered activated and supplied with hydrogen gas by an internal supply for 10 months. Then, the hydrogen cells can be replaced. The hydrogen inside the shaft ensures the controlled electrolyte output out of the diaphragm. However, if measuring solution enters the electrode the interior electrolyte can be replaced. pHydrunio is made of polypropylene and thereby indestructible.

Thus, it can be used in highly alkaline or acid electrolytes as well as in concentrated fluoride media.

The shaft is 120 mm long and the diameter is 12.2 mm. A PG 13.5 thread enables the installation in appropriate armatures. The measuring electrode is protected from mechanical damages.

Our platinum hydrogen pH-electrode is low-resistant in contrast to common glass electrodes. For the measurements we recommend the multimeter Peaktech.

Aufbau der Platinwasserstoff-pH-Elektrode pHydrunio

Structure of the platinum hydrogen pH-electrode pHydrunio

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Commissioning and maintenance

The platinum hydrogen pH-electrode pHydrunio is delivered pre-assembled which means the hydrogen cells are already installed and activated. On the electrode’s head you can find a label which states the month of activation. Do not remove that label! pHydrunio is already filled with an interior electrolyte.

Before you start your measurements please place the hydrogen pH-electrode in the provided calibration buffer pH 7 for 24 hours.

Do not remove neither the label with the month of activation nor the label with the serial number.

Commissioning of the hydrogen pH-electrode pHydrunio

Commissioning of the hydrogen pH-electrode pHydrunio

Storage of the platinum hydrogen pH-electrode pHydrunio

After your measurements rinse the electrode thorough with water. Please, always place the pH-electrode in the provided calibration buffer pH 7 if you do not measure. The platinum hydrogen pH-electrode must not be stored dry in air as long as the hydrogen cells generate hydrogen. When the run time is exceeded the hydrogen cells have to be replaced immediately.

Replacement of the hydrogen cells

pH-electrode pHydrunio

You can easily replace the hydrogen cells of the hydrogen pH-electrode pHydrunio

The functioning of the hydrogen pH-electrode is ensured as long as hydrogen is generated (runtime). The run time is 10 months. When the run time is reached the hydrogen pH-electrode must not placed in a liquid, anymore. The hydrogen cells have to be replaced immediately.

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Calibration of pHydrunio

First of all, the pH-electrode is placed in calibration buffer pH 7 (Gaskatel). Thereby the deviation from the zero point is determined. According to the condition of the electrode it can last several minutes. Note the measured voltage and the temperature of the buffer as soon as the voltage has become constant.

Then, rinse the electrode and the temperature sensor with water before you place both in calibration buffer pH 0 (Gaskatel). Note the measured voltage and the temperature of the buffer as soon as the voltage has become constant. Waiting times of several minutes are possible.

Inspection of the functioning of pHydrunio

You can check both electrodes in the hydrogen pH-electrode separated from each other against a so-called master electrode, e.g. a calomel electrode. The master electrode should always be placed in appropriate potassium chloride solution and not be used for other purposes.
Pay attention to the fill level in the calomel electrode itself. It must always be above the fill level in the measuring vessel. Open the filling plug of your calomel electrode to prevent the measuring fluid from entering the calomel electrode.

To check the hydrogen pH-electrode pHydrunio, place pHydrunio and the master electrode in buffer pH 0. Connect the calomel electrode to the positive pole. To contact the pH-electrode you need an appropriate adapter BNC on 4 mm laboratory socket. Now, connect the red socket of the adapter with the negative pole (COM-port) of your voltmeter. You are now checking the outer measuring electrode of the hydrogen pH-electrode. After an adjustment phase, which can last several minutes, you read off the potential. Now, connect the black socket of the adapter with the negative pole (COM-port) of your voltmeter. You are checking the inner reference electrode of your pH-electrode. After an adjustment phase, which can last several minutes, you read off the potential.

The following table shows the to expecting potentials. It is assumed that the pH-values stay constant in these temperature ranges. Diffusion voltages are not considered.

Download Potentials in buffer pH 0
table ph-electrodes

The outer and the inner pH-electrode can be checked separated from each other. We recommend checking it in buffer pH 0.

Replacement of the internal buffer

The internal buffer (reference electrolyte) can be replaced. Therefore, the sealing cap at the electrode’s head must be unscrewed. You can pull the internal buffer out with the provided syringe and cannula.

Rinse out the electrode with distilled or deionized water. Fill in the new internal buffer directly out of the vial. Screw down the pHydrunio carefully. Place pHydrunio in calibration buffer pH 7 for 24 hours.

Troubleshooting

The potential is not displayed correctly

Cause 1: bad contacting
Check the measuring cables on optical damages such as corrosion, cracks and sessile plugs. Replace the cable. Check both electrodes with an external reference electrode, e.g. a silver silver chloride electrode.

Cause 2: no or too low hydrogen production
Is the run time of the cartridge exceeded? If yes, please replace the hydrogen cell.

Cause 3: internal buffer is contaminated
It can happen that measuring solution enters the internal buffer and contaminates the internal buffer. In that case, the internal buffer has to be replaced.

Cause 4: slow ion exchange, e.g. when you switch from concentrated solutions to weak concentrated solutions
Await the setting time, sometimes the balancing of concentrations lasts longer than expected. If necessary, check the potential in another electrolyte, e.g. in one of the provided calibration buffers.

Cause 5: air/oxygen gets to the hydrogen electrode
Avoid that gases such as air or oxygen reach the platinum hydrogen electrode’s shaft. If this happens the hydrogen is displaced or reacts off and no hydrogen potential can be set.

Fluctuating, noisy or oscillating potentials

Cause 1: Hydrogen bubbles of the hydrogen electrode itself
Bubbles are continuously leaking out of the platinum hydrogen electrode. Some bubbles are small, others are bigger. Usually, they do not disturb your measurements.
Is a big bubble forming at the bottom of the hydrogen electrode which sticks to the vessel wall? If Possible, place the electrode further away from the vessel wall or hang the hydrogen electrode transversely into the measuring vessel.

Cause 2: Induced gases
Change the position of your gas inlet. Induced gas bubbles which are piped by close to the hydrogen electrode can disturb the measurements and lead to fluctuating potentials.