Dissolved Oxygen and pH Monitoring System

What is the Dissolved Oxygen and pH Monitoring System?

A dissolved oxygen and pH monitoring system uses sterilisable electrochemical or optical probes to measure oxygenation and acidity continuously, providing the feedback needed for bioreactor control and for detecting oxygen limitation in cultures.

Overview

Dissolved oxygen probes are either galvanic or polarographic, consuming a small amount of oxygen at a membrane, or optical, using a luminescent dye whose emission is quenched by oxygen. pH probes use glass electrodes or optical sensors with a pH-sensitive dye. Both types can be steam-sterilised in place or supplied as single-use sensors pre-installed in a bag or vessel. Signals feed cascade controllers that adjust gas flow, oxygen enrichment, agitation or base addition to hold set points, typically 40–60% air saturation for oxygen and pH 6.9–7.4. Response time, accuracy and drift differ between technologies, and readings are affected by temperature, so temperature compensation or simultaneous measurement is required. Trend data also reveal oxygen limitation, which is the most common constraint on cell density.

How does it work?

Monitoring methods translate a physical or chemical property of the culture into a usable signal. Imaging systems illuminate the culture surface and estimate confluence from the fraction of the area occupied by cells, or count fluorescent objects to give viable cell density. Capacitance probes apply a radio-frequency field across the culture; viable cells with intact membranes behave as polarisable particles whose signal is proportional to viable cell volume, while dead cells and debris contribute little. Dissolved oxygen is measured with electrochemical or optical sensors, and pH with glass or optical sensors, both of which can be steam-sterilised for bioreactor use. Metabolite analysers use enzyme-based or optical assays to quantify glucose, lactate, glutamine and ammonia in culture samples. Raman spectroscopy adds in-line multi-component measurement when a chemometric model has been calibrated for the process.

What are the key features?

• Electrochemical or optical dissolved oxygen measurement
• Glass electrode or optical pH measurement
• Steam-sterilisable or single-use sensor options
• Cascade control of gas flow, agitation and base addition
• Temperature compensation or integrated temperature sensor
• Continuous logging with alarm limits

What are the technical specifications?

A typical dissolved oxygen and ph monitoring system configuration offers dissolved oxygen range of 0–200% air saturation, dissolved oxygen accuracy of within ±2% air saturation (typical), pH range of pH 2–12, pH accuracy of within ±0.05 pH units after calibration, response time of approx. 10–60 s and sterilisation of Autoclave, in-situ steam or gamma for single-use. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Dissolved Oxygen and pH Monitoring System is used in bioreactor oxygen and pH control, detection of oxygen limitation at high density, media buffering assessment and scale-up and process characterisation. Across the wider Culture Monitoring class, laboratories also deploy it for feeding and harvest timing decisions, bioreactor process control and scale-up and contamination and stress detection.

Which standards and certifications apply?

Relevant standards and methods include IEC 61010-1, IEC 61326-1, ISO 14644-1, USP <1046> and ISO 20387. Certification candidates for this model are CE, ISO 9001 manufacturing and IEC 61010-1 safety; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Calibrate each sensor against the reference method used in your laboratory, and record the calibration coefficients, since drift differs between probe types and affects decisions. For optical sensors, check the excitation wavelength and the dye's sensitivity to pH, ionic strength and temperature, which must be matched to the culture conditions. Capacitance probes require a defined conductivity window, so the medium formulation cannot change without re-validation. Sampling for metabolite analysis should be consistent in timing and dilution, and the analyser should be checked with standards daily. Clean and sterilise probes according to the manufacturer's instructions, since residues from previous runs cause drift, and replace consumable sensors at the recommended interval rather than at failure. Keep trend data rather than single values, because rates of change are usually more informative.

How do I select the right Dissolved Oxygen and pH Monitoring System?

Select monitoring probes when oxygen or pH control is part of the process or when oxygen limitation must be detected before growth slows. Specify measurement ranges, accuracy, sterilisation method, probe size, response time and integration with the bioreactor control system.

How does it compare with other Culture Monitoring variants?

Decide what decision the data must support. If the question is when to passage or harvest an adherent culture, automated confluence imaging is sufficient and simple. If viable cell density drives feeding or infection timing, capacitance biomass monitoring provides a real-time signal without sampling. For process control in a bioreactor, dissolved oxygen, pH and temperature probes are essential, and metabolite analysis adds the information needed to adjust perfusion or feed rates. Raman or near-infrared in-line analysers are justified only when the modelling effort can be sustained and the process runs often enough to benefit. Check measurement range and accuracy, response time, sterilisation method, whether the sensor contacts the culture, calibration and drift behaviour, integration with control software, and the frequency of consumable or probe replacement.