pH and Oxygen Measurement Alternative Oxygen Measurement Trend: Advantage for ARC-Sensors

Editor: Anke Geipel-Kern

Electrochemical Clark oxygen sensors are well established for a long time, but optical measuring is coming around the corner, and scores with many advantages — another reason why a biotechnology specialist offers his customers optical sensors as state-of-the-art solution.

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Arc Sensor mounted on a bioreactor.
Arc Sensor mounted on a bioreactor.
(Picture: Hamilton/MCE)

From a historical perspective to the present day Bilfinger Industrietechnik Salzburg is a true knowledge carrier in the biotechnology sector. Bioreactortechnology is a core business of the systems engineering business unit and the specialists are always searching for state-of-the-art-sensor technology.

Since some years the company, originally have emerged from the Mannesmann history and later part of MCE, counts on Arc sensors from Hamilton. Parameters like the pH value, dissolved oxygen and conductivity are essential to maintain the process in the bioreactor and to achieve the goal of controlled product quality.

“We have been working with the sensor specialists from Hamilton Bonaduz in this field for many years already,” states Dipl.-Ing. Gerald Berghammer, Head of the Biotechnology, Pharmaceuticals and Fine Chemicals business unit at Bilfinger Industrietechnik Salzburg. In addition to exact measurement, the sensors used have to meet the legal requirements regarding possible contamination.

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Contrary to customers’ expectations, this is often lacking. “There are enough sensors in the market. But many are unsuitable because sterility cannot be ensured,” says Pablo Pino-Grace, Project Engineer and responsible for the bioreactor product group at Bilfinger Industrietechnik. Pino-Grace adds that, with the decision to favor Hamilton and the Arc product family, sensors have been implemented which, amongst others, withstand the frequent sterilization processes as well.

pH and Oxygen Sensors Yesterday and Today

In the past, electrochemical Clark sensors were commonly used for measuring dissolved oxygen in the biotechnology sector. In their measuring chambers, a platinum cathode and a silver anode are usually connected by an electrolyte solution, with the polarization being set so that electrolysis of the electrolyte solution does not occur. Oxygen diffuses through a permeable membrane in the sensor cap into the measuring chamber.

The consequential measuring current allows determining the partial pressure of the dissolved oxygen. Even though Clark sensors have been established for a long time, they have significant disadvantages compared to optical sensors: Next to time-consuming polarization, the membrane is mechanically very sensitive and, along with the electrolyte solution, has to be replaced frequently. Furthermore, deposits of oxidized silver metal occur on the anode as a consequence of the measuring process. The deposits have to be removed to ensure the high conductivity of the electrode. Process control is therefore more difficult because a lot of maintenance is required.

Discover a new trendsetter in pH and oxygen measurement – on page two...

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