ION SENSITIVITY

Figure A3.14.5. Experimental reeords from Pt and Br -ion-sensitive eleetrode for the BZ reaetion in bateh showing regular oseillatory response.

Alkalinity (Soluble Soda) Determination. The surface alkalinity or soluble or leachable soda is determined by making a fixed weight percent slurry in water and determining the alkalinity of the solution by pH measurement or acid titration. Sodium ion-sensitive electrodes have been investigated. 

An interesting effect is sometimes observed when cupronickels are galvanically coupled to less noble materials. The corrosion rate of the active metal is increased and the corrosion rate of the cupronickel is diminished, as expected. The diminished corrosion rate of the cupronickel can, however, diminish its fouling resistance since reduced production of copper ions lowers toxicity to copper-ion-sensitive organisms. 

Figure 1 Schematic diagram of a Mattauch-Herzog geometry spark source mass spectrometer using an ion-sensitive plate detector.

Mattauch-Herzog geometry, which simultaneously focuses all resolved masses onto one plane, allowing the integrating properties of an ion-sensitive emulsion to be used as the detector. Although electrical detection with an electron multiplier can be applied, the ion-sensitive emulsion-coated glass photographic plate is the most common method of detection and will be described in this article. 

Figure 2 Ion-sensitive plate detector showing the species produced by the SSMS analysis of a Y203 Eu203 mixture compacted with gold powder.

Due to the relative uniformity of ion formation by the RF spark (although its timing is erratic), the most widely used method of quantitation in SSMS is to assume equal sensitivity for all elements and to compare the signal for an individual element with that of the total number of ions recorded on the beam monitor. By empirically calibratii the number of ions necessary to produce a certain blackness on the plate detector, one can estimate the concentration. The signal detected must be corrected for isotopic abundance and the known mass response of the ion-sensitive plate. By this procedure to accuracies within a factor of 3 of the true value can be obtained without standards. 

In practical terms, it is suggested that, in any application where the presence of halide ions may cause problems, the concentration of these be monitored to ensure the purity of the liquids. This may be achieved either by the use of an ion-sensitive electrode, or alternatively by use of a chemical method such as the Vollhard procedure for chloride ions [52]. Seddon et al. have reported that effectively identical results were obtained with either method [37]. 

Sampling points for analysis should be planned in order to give the whole record of analysis, e.g. in oil production from the well via processing facilities to the export facilities. Correlation with plant parameters such as temperatures, pressures, flow rates and, stream compositions can provide valuable records. Emphasis on chemical analysis should be incorporated in the design of process plant. Automatic analysis systems especially those using ion-sensitive electrodes with recording of data are recommended. 

As early as 1937, Kolthoff and Sanders32) used silver halide discs as ion-sensitive membranes for the corresponding anion. They found that interferences through redox-systems were negligible with those membranes compared to electrodes of... 

Moody, G. J., Thomas, J. D. R. Selective Ion Sensitive Electrodes, Watford, Merrow 1971... 

In acid-base titrations the end point is generally detected by a pH-sensitive indicator. In the EDTA titration a metal ion-sensitive indicator (abbreviated, to metal indicator or metal-ion indicator) is often employed to detect changes of pM. Such indicators (which contain types of chelate groupings and generally possess resonance systems typical of dyestuffs) form complexes with specific metal ions, which differ in colour from the free indicator and produce a sudden colour change at the equivalence point. The end point of the titration can also be evaluated by other methods including potentiometric, amperometric, and spectrophotometric techniques. 

Glass electrodes are responsive to univalent cations. The selectivity for these cations is achieved by varying the composition of a thin ion-sensitive glass membrane. 

Instead of using an indicator, an ion-sensitive electrode can be used. An aqueous solution is titrated potentiometrically against 0.04 N hyamine 1622 solution using a nitrate ion-selective electrode and a silver/silver chloride reference electrode [106]. 

Jasinski R, Trachtenberg I (1973) Evaluation of the ferric ion sensitive chalcogenide glass electrode. J Electrochem Soc 120 1169-1174... 

Fig. 2.16. Ion-sensitive field effect transistor (intersection and symbol), (a) n-p-n transistor, (b) IGFET (MOSFET), (c) ISFET.

Thomas, R. C., Ion-Sensitive Intracellular Microelectrodes. How To Make and Use Them, Academic Press, London, 1978. 

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