Portable oxygen measuring instrument

Disaster was adverted when a safety technician entered the control room as part of an unrelated confined space entry permit. The technicians portable oxygen measuring instrument was activated and in the operating mode. The low-level oxygen alarm sounded, warning the people in the control room of the very serious condition. 

There is a longstanding demand for a simple and portable instrument for the detection and measurement of oxygen dissolved in water. Suitable electrodes have been developed and more recently have been ingeniously used as the basis for a range of biochemical sensors. 

The measurements of water quality parameters (oxidation-reduction potential, pH, temperature, conductivity, dissolved oxygen, and turbidity) and the collection of field screening data with field portable instruments and test kits constitute a substantial portion of field work. Field measurements, such as pH, stand on their own as definitive data used for the calculations of solubility of chemical species and chemical equilibrium in water, whereas others serve as indicators of well stabilization or guide our decision-making in the field. Table 3.8 shows the diversity of field measurement... 

A sampling campaign has been carried out in summer 2000, with nine points located along the river (Fig. 4). For each station, the UV spectrum and the measurement of dissolved oxygen, conductivity and pH have been realised on fresh samples. A field-portable UV spectrophotometer (Pastel UV from Secomam) and handheld instruments for the other parameters have been used. 

Benchtop conductivity meters are not as prevalent now, as portable and handheld devices have become commercially available. These are discussed further in the sections on portable instruments and process instruments. The conductivity meter is often combined with other electrochemical measurements on the same device, e.g. pH or dissolved oxygen. 

Portable analysers are available which measure the concentration of oxygen in the air by the depolarisation produced at a sensitive electrode mounted in the instrument (Figure 18.5). Several different devices are available which vary in sensitivity, reliability and ease of maintenance but they must all be checked and carefully calibrated to the manufacturer s... 

In general, on-stream analyzers are not as reliable as lab analysis and should not be used. However, for measuring the oxygen content of furnace flue gas or the H2S and SO2 content of sulfur-bearing gas streams, portable analyzers are best. These portable instruments need to be obtained and calibrated in advance. 

Potentiometric stripping analysis (PSA) is another commonly used technique in water analysis. This technique can usually be applied directly to the analysis of water samples without previous treatment, and it is virtually free from interferences of dissolved oxygen. Both, PSA and ASV techniques are based on the same principle the anal) e is first deposited on the electrode surface while the solution is stirred, and then stripped back to the solution in the measurement step [14,22,196]. The ASV technique works on a film electrode (electrochemically deposited mercury or gold on a glassy carbon support). One advantage of PSA is that it requires simpler equipment than ASV, and can compete with nonelectroanalytical techniques in terms of price, and possibility of automation [247-249]. This method has been applied to determine metals in tap water and rainwater samples [250-253], coupled with FIA to determine copper in natural waters [254,255], etc. In addition, portable PSA instruments have also been developed, and demonstrated to be useful for metals determination in aquatic samples [256-259]. 

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