Electrochemical interferences instrumentation

In electrochemical cells sample oxidation produces an electric current proportional to the concentration of test substance. Sometimes interferences by other contaminants can be problematic and in general the method is poorer than IR. Portable and static instruments based on this method are available for specific chemicals, e.g. carbon monoxide, chlorine, hydrogen sulphide. 

In the past decade, effects of an EEF on the properties of lubrication and wear have attracted significant attention. Many experimental results indicate that the friction coefficient changes with the intensity of the EEF on tribo-pairs. These phenomena are thought to be that the EEF can enhance the electrochemical reaction between lubricants and the surfaces of tribo-pairs, change the tropism of polar lubricant molecules, or help the formation of ordered lubricant molecular layers [51,73-77]. An instrument for measuring lubricant film thickness with a technique of the relative optical interference intensity (ROII) has been developed by Luo et al. [4,48,51,78] to capture such real-time interference fringes and to study the phenomenon when an EEF is applied, which is helpful to the understanding of the mechanism of thin film lubrication under the action of the EEF. 

Other methods have been developed for the removal of oxygen (particularly from flowing streams).These include the use of electrochemical or chemical (zinc) scrubbers, nitrogen-activated nebulizers, and chemical reduction (by addition of sodium sulfite or ascorbic acid). Alternately, it may be useful to employ voltammetric methods that are less prone to oxygen interference. The background-correction capability of modern (computerized) instruments is also effective for work in the presence of dissolved oxygen. 

Using electrochemical sensors and considering the sources of uncertainty given by Pan [2], viz. homogeneity, recovery, analysis blank, measurement standard, calibration, matrix effect and interferences, measuring instrument, and data processing, the main uncertainty sources i.e., the homogeneity and the matrix effect, are eliminated. 

Most of transduction elements used in enzyme-based biosensors are electrochemical amperometric or potentiometric. Typically the enzymes used in amperometric biosensors are oxidases. The main advantages of this class of transducer are the low cost a high degree of reproducibility, and the suitability of many of them for incorporation into disposable electrodes. This type of instrumentation is widely available and can be inexpensive and compact this allows this makes it possible to use them for making on-site measurements. Limitations of amperometric measurements include potential interferences to the response from any electroactive compounds that are present in... 

Because electrochemical experiments involve a direct conversion of chemical information to electricity, the instrumentation can be relatively simple. There is, for example, no need for high-quality power supplies to drive a light source or operate a photomultiplier tube. On the other hand, because the process often measures nanoamperes (or less) of current, electrochemical detectors are particulariy subject to dectrical interferences, and proper grounding can be crucial to successful experiments at high current-to-voltage gains. 

There are two methods that are predominantly used to analyze CO these are based on infrared (IR) absorption and electrochemistry. The IR technique is based on the fact that CO will absorb light at 4.67 pm (2165 cm ). The CO concentration is then determined from the extent of absorption of the sample. There are two types of analyzer design, known as nondispersive and gas filter correlation analyzers. Interferences from CO2 and water vapor can be overcome by instrumental design and are generally not significant. Reported detection limits are <0.5mgm for this technique. The electrochemical cell technique is based on the electrochemical detection of CO as it is oxidized to CO2. Interferences from other oxidizable gases can be minimized by the use of special inlet filters and the detection limits obtained are comparable to the IR technique described earlier. 

Despite the extensive studies of the anodic layers on Pt with various ultraviolet-visible optical methods, they have not provided a clear indication of the electronic or structural properties of the layers. Rather these optical methods have been more than just another form of readout to complement the electrochemical measurements of charge and current response of the layer to potential and time. Vibrational spectroscopic data from infrared and Raman measurements would be more helpful in establishing the nature of the layers but it is difficult to use these techniques to study metal-electrolyte and similar interfaces because of solvent interference and sensitivity problems. A noteworthy exception is the quite successful in situ use of Raman spectroscopy to study the electrochemically formed oxide layers on silver by Kotz and Yeager. In the instance of silver electrodes, there is a large surface enhanced Raman effect and the signal-to-noise ratio is not a problem. Unfortunately this is not the situation with other metal surfaces such as Pt. Even so, with improved instrumentation there is hope that in situ Raman studies of the anodic layers on Pt will become practical. 

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