Calibration oxygen sensors

Hartmann P., Trettnak W., Effects of polymer matrices on calibration functions of luminescent oxygen sensors based on porphyrin ketone complexes, Anal. Chem. 1996 68(15) 2615-2620. 

Figure 13.10 shows the calibration curve of the LED-based optical oxygen sensor compared with the calibration curve of a commercially available Clark-type sensor (Ingold Electrodes, Wilmington, Massachusetts). While the Clark-type shows a linear calibration, the optical sensor allows a hyperbolic response as predicted by the Stem-Volmer-type equation 72 ... 

When rebreathing systems are used for the delivery of xenon, its concentration within the system needs to be closely monitored. Infrared gas analysers cannot detect xenon, since it is a single atom, and as it is chemically inert its physical properties must be utilised. Mass spectrometry is the most accurate method but it is expensive and it is impractical for clinical use. A calibrated katharometer combined with a galvanic oxygen sensor is a satisfactory alternative which provides a reasonably accurate measure ( 1%). 

Fig. 8.6 Calibration plot of oxygenate sensor-1 for total oxygenate compounds produced by catalytic propane oxidation the yield of each oxygenate was determined with a conventional FID gas chromatograph (reproduced by permission of Elsevier from [19]).

USE OF OXYGEN SENSORS AS A SURROGATE GLUCOSE SENSOR FOR IN VIVO TESTING AND IMPORTANT ISSUES RELATED TO IN VITRO SENSOR CALIBRATION... 

Makale MT, Jablecki MC, Gough DA. Mass transfer and gas-phase calibration of implanted oxygen sensors. Analytical Chemistry 2004, 76, 1773-1777. 

The uncertainty of commercial calibration gas mixtures is typically 1% of the amount fraction, and the contribution of this to the overall measurement uncertainty is much greater than the intrinsic error of the oxygen sensor for amount fractions of oxygen that are 0.1 ppm and above [2]. Consequently, test procedures that require calibrated gas mixtures will be limited by the uncertainty of those gas mixtures, and therefore carmot be used to test the accuracy of oxygen and other zirconia-based gas sensors, assuming the uncertainty of the sensor calibration is no worse than that of the test mixtures. At present, the uncertainty of commercial calibration gas mixtures is a limitation to verifying the accuracy of these gas sensors. 

The calibration curve for the oxygen sensor operated at —0.55 V fits a linear least-squares fit well (R = 0.993), but exhibits a slight sublinearity. Interestingly, the calibration curve obtained at a potential of —0.65 V does not show this sublinearity. This evidence points towards the rate of the electrochemical reaction itself being the rate limiting step in the gas sensing process. 

A function check, or bump test, means using simple tests (such as exposing sensors to calibration gas or exhaling into the oxygen sensor) to show that the instrument will respond to the chemicalfs) of concern and that aU alarms operate as they were designed. Functional Safety Assessment... 

The main requirement in the use of membranes in the construction of oxygen sensors is that the membrane must be permeable to oxygen, while restricting the passage of water and electrolyte. On this basis, the use of a single point calibration method based on the use of air, with the assumed linearity of response for other measurement, is feasible. Another calibration method involves the use of solutions previously verified by the Winkler oxygen titrimetric method. 

Independent of the brand of polarographic oxygen sensor, a general calibration procedure has to be followed. The geometry and the membrane of the sensor define, within limits, the diffusion layers and consequently the temperature dependence of the oxygen probe. 

It has to be noted that the calibration of dissolved oxygen sensors of the Clark type requires homogeneous temperatures from the cathode to the seawater environment. Whenever the probe-body temperature differs from the environment, the diffusive fluxes are not defined and the calibration is not valid. Most sensors require thermal equilibration times of about 20 s or more due to their considerable heat capacities, which is considerably longer than the response times. 

Figure 4 Calibration plot for the oxygen sensor at varying pressures.

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