Electrode slope

There are two types of fluoride lon-selective electrodes available [27] Onon model 96-09-00, a combination fluoride electrode, and model 94-09-00, which requires a reference electrode The author prefers to use Onon model 94-09-00 because it has a longer operational life and is less expensive When an electrode fails, the reference electrode is usually less expensive to replace The Fisher Accumet pH meter, model 825 MP, automatically computes and corrects the electrode slope It gives a direct reading for pH, electrode potential, and concentra tion in parts per million The fluoride lon-specific electrode can be used for direct measurement [2S, 29] or for potenPometric titration with Th" or nitrate solutions, with the electrode as an end point indicator... 

The pH (or pI) term of the Nemst equation contains the electrode slope factor as a linear temperature relationship. This means that a pH determination requires the instantaneous input, either manual or automatic, of the prevailing temperature value into the potentiometer. In the manual procedure the temperature compensation knob is previously set on the actual value. In the automatic procedure the adjustment is permanently achieved in direct connection with a temperature probe immersed in the solution close to the indicator electrode the probe usually consists of a Pt or Ni resistance thermometer or a thermistor normally based on an NTC resistor. An interesting development in 1980 was the Orion Model 611 pH meter, in which the pH electrode itself is used to sense the solution temperature (see below). 

In the Model 811 the various settings of the mode switch yield pH, solution temperature, electrode potential, electrode slope and time of day an illuminated push-button signals the moment that stable readings have been obtained. Two-point standardization may be carried out on any pair of buffers in any order. 

Molybdenum disulfide electrodes, sloping discharge curve, 3 414 Molybdenum ditelluride, 17 26 Molybdenum enzymes, 17 321 Molybdenum hexacarbonyl, 7 594 ... 

Titanium disulfide, 25 57, 58 Titanium disulfide electrodes sloping discharge curve, 3 414 Titanium esters, 25 1 Titanium fluorides, 25 47-49 Titanium halides, 25 47-55 Titanium hydride, 13 626 Titanium hydrides, 25 5 Titanium-hydrogen system, 25 3-5 phase diagram for, 25 5 Titanium iodides, 25 54-55 Titanium/isopropoxy/nitrilotriethoxy ratio, 25 93... 

The system is continuously monitored to alert the operator to errors such as antigen excess, high background fluorescence readings, loss of sample/reagent integrity and deterioration of electrode slope range. 

Electrode Slope, mV/log a Concn. Range of Linear Response, M Useful Concn. Range, M... 

Alternatively, the analysis may be performed by standard addition method (see Chapter 1.9) in which no calibration curve is required. Prepare an NH3 standard solution that is about 10 times as concentrated as the estimated concentration of NH3-N in the sample. Determine the electrode slope following the instruction manual. To 100 mL sample, add 1 mL 10 A NaOH and immerse the electrode and stir the solution. Record the millivolt value Ex when the reading is stable. Add 10 mL of standard solution into the sample. Mix thoroughly and record the stable millivolt reading E2. Calculate the millivolt difference AE as E2 - E and determine the concentration, Cx mg NH3-N/L, from the following expression ... 

D) The electromotive loss factor n yields details of the interfacial equilibrium which have hitherto been unknown. Thus, a combination of n = d log a R- / dpH and the practical electrode slope (1-n) k, which is between 58 and 59.1 mV (25 °C), gives the internal slope d m/dloga R = -(1 - n)k/n. Depending on n, it amounts to between -11.8 and -59.1 volt for the average n = 0.0025, it is 23.6 volt. n thus divides the practical electrode slope into a minute, more chemical , and a very large, more physical , part of the equilibrium, n is a finite quantity, n > 0, that can approach but cannot be equal to zero. 

The magnitude, presented in Figure 17.8(b), tends toward Re as frequency tends toward oo and toward oo as frequency tends toward zero. The slope of the line at low frequencies has a value of —a for the blocking electrode. Slopes with values smaller than unity could provide an indication of a blocking electrode with a distribution of characteristic time constants. The slope of the modulus corrected for Ohmic resistance is equal to —a for all frequencies. 

The influence of chloride ions on electrochemical behaviour of copper(II) sulphide, both in open-circuit and voltammetric experiments, is a result of the electrochemical reactions (9) and (10) of the redox reaction (8). In the case of open-circuit measurements with the increase of chloride ion concentration the increase of electrode slope is observed and can be assigned to the change of potential determining reaction from (9) to (11), As a consequence two limiting slopes are observed divalent (29.6 mV/decade) in absence of chloride ions and monovalent (59.2 mV/decade) in 1 M KCl. The voltammetric behaviour of CuS is also influenced by the same reaction, although with increase of pH reaction (12) instead of reaction (11), controls... 

It is obvious that the relation between pX and AE(AE=Ex-Es) is linear. S is theoretic slope of the electrode system however, the actual electrode slope is also... 

The electrode slope s and the constant potential term Ki are determined by calibration. 

Use a Z or half-moon oscillation with adequate arc length, travel speed and electrode slope. 

Concentration Determinations with the Heip of a Standard Addition with a Known Electrode Slope S... 

With the double standard addition method it is not the electrode slope precisely at the sample concentration which is determined, but rather the slope in a somewhat more concentrated region (between Cx + AC and Cx + 2 AC), By diluting the solution after the first addition, a slope can be obtained much nearer to the sample concentration. In this procedure, as usual, a known amount of standard measured ion solution is added and the EMF change AEad is noted. For this a concentration change AC approximately that of the sample solution is chosen. To position the working point precisely in the middle, the solution is then diluted 1 1. The EMF change due to this dilution AEd is also noted. The slope of the electrode used can then be calculated with the following equation ... 

Let us suppose our desired accuracy is 2%, so we select a method making use of a known electrode slope and employ a reference electrode with a sleeve diaphragm. From the considerations in Chap. 

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