Flow-thru cells

Unfortunately there are no generally valid rules for industrial measurement techniques. The commercially available instruments are usually flexible enough, however, to be compatible with the flow schemes in other special applications. The manufacturers also have the most recent, detailed procedural directions available for many of the substances listed in Table 7. As a representative example, the problems associated with automating one particular determination will be discussed here. First, however, the flow-thru cell itself and some error-determining parameters will be briefly discussed. 

The flow-thru cell constructions already long employed for industrial pH measurements can also be used with ion-selective electrodes. Here the reference electrode is positioned further along in the flow direction than the indicating electrode to avoid interferences from outflowing reference electrode electrolyte. A sin e reference electrode can be used with a number of different ion-selective electrodes placed in the sample channel. If the individual electrodes are placed in the center of the sample stream, quick responses to activity changes can indeed be obtained, but streaming potentials (see Chap. 1.2) of up to 1.3 V, depending on the conductivity, sample channel diameter and flow rate, must be dealt with. Van den Winkel, Mertens and 

Sample streams contaminated with particulate matter can be filtered before analysis, as shown in Fig. 58. Ehie to the self-cleaning effect of a horizontal flow, such filters can even be used with highly contaminated samples for over a month without changing the filter [437], 

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In these bio-related fields, it is primarily the pH, pNa, pK, pCa, pCl or pF electrodes which are employed. Depending upon whether extra- or intracellular ion activities are to be determined, different electrode constructions are utilized. Measurements in extracellular fluids (whole blood, serum, etc.) are usually carried out with the conventional macroelectrodes. Anaerobic conditions are harder to maintain with this method.is expedient to thermostat the entire sample beaker and electrode pair set-up. For more accurate pH and pCa determinations the air space above the sample must also be equilibrated with an O2-CO2 mixture, to establish the same partial pressure of CO2 as in the original sample environment. This expense can be spared by working with microprobes under anaerobic conditions with small surface areas (low CO2 loss). In such cases the commercially available flow-thru cells or capillary cells are used. For ion activity measurements within the cell special microelectrodes with tip diameters about one micron are employed, so that the cell membrane is not damaged too much. To date, such electrodes are available only for pH and pNa measurements (Transidyne, U.S.A.). 

The last section describes special set-ups such as clinical flow-thru cells, microelectrodes for measuring intracellular ionic activities, industrial on-line techniques and continuous environmental protection monitors. 

Fires - Radioactivity and the Detection of Fires, An electronic detector apparatus responds to changes in current flowing thru an ionization cell containing an o-particle source. The presence of smoke particles, fumes, or vapor in the cell will change the current flowing in the apparatus and activate an alarm... 

The electrochemical cell used for the electropolymeiization is of a unique design and has been described elsewhere (17) The electrochemical cell used in the FIA/anion analysis was a commercial flow-thru electrochemical cell available from BAS. 

Fig. 61. Concentration cell construction for industrial flow-thru systems...

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