Important measurements using specific electrodes

Combined measuring probe Has a thin-walled glass bulb at its tip which detects H+ ions in solution, and produces a small voltage (around 0.06 V per pH unit), and as such provides a signal related to the concentration of H+ ions which can be converted into a measurement of pH. For simplicity, the pH probe can be 

Using a pH meter Before taking pH readings it is important that the user checks the components of the system, paying particular attention to the measuring probe (e.g. level of KCl and integrity of glass bulb) and temperature control (which 

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Surfactant Activity in Micellar Systems. The activities or concentrations of individual surfactant monomers in equilibrium with mixed micelles are the most important quantities predicted by micellar thermodynamic models. These variables often dictate practical performance of surfactant solutions. The monomer concentrations in mixed micellar systems have been measured by ultraf i Itration (I.), dialysis (2), a combination of conductivity and specific ion electrode measurements (3), a method using surface tension of mixtures at and above the CMC <4), gel filtration (5), conductivity (6), specific ion electrode measurements (7), NMR <8), chromatograph c separation of surfactants with a hydrophilic substrate (9> and by application of the Bibbs-Duhem equation to CMC data (iO). Surfactant specific electrodes have been used to measure anionic surfactant activities in single surfactant systems (11.12) and might be useful in mixed systems. ... 

These results suggest that interactions between silicate species and surfactant micelles are weak in the precursor solution. The absence of any organization in the system prior to precipitation seems to indicate that the most important step in the process is the formation of siliceous prepolymers. The interaction of these prepolymers with surfactants could be responsible for micelle growth and subsequent reorganization of the silica/micelle complexes into ordered mesoporous structures. Such a hypothesis might be confirmed by preliminary potentiometric measurements using a bromide ion-specific electrode the amount of free bromide anion increasing at pH around 11 when the polymerization of silica starts. 

Analytical schemes concerned with the determination of blood ions and gases can be divided into two categories analyses done in vivo and those done in vitro. By far the most common method of determining blood ions in vitro involves atomic spectroscopy. Atomic absorption and flame emission have both been used although the latter is the most popular. In the clinical lab nearly all of the remaining determinations (both in vivo and in vitro) are performed with ion-selective (for ions, NH3 and CO2) or amperometric electrodes (O2 and H2). Two important characteristics of ion-selective electrodes, sensitivity and selectivity, should be mentioned. The applicability of a specific electrode in any particular situation can be determined by considering, on one hand, the ionic constituents of the solution to be measured and, on the other hand, the sensitivity and specificity of the electrode in question. Proper consideration of these points will allow an investigator to determine the accuracy and validity of the measurement. 

The cmc and micelle ionization degrees near the cmc (9) were determined by emf measurements using a specific bromide ion electrode (Orion 9435), in conjunction with a double junction reference electrode (Orion 9002) and a millivoltmeter (Orion 701A). Some determinations were also performed by means of conductivity. It was noted that emf measurements yielded cmc values slightly lower than those obtained from the equivalent conductivity vs. (concentration) plots. This, however, is of no importance in this work where we are only interested in relative changes. 

There are some major differences between electrochemical engineering and classical electrochemistry. In conventional electrochemistry the mechanism of the electrode process and its kinetics are often the factors of major concern whereas in electrochemical engineering the actual mechanistic details of the process are usually less important than its specificity or process efficiency. The rate of the process defined either as current efficiency or as a general measure of reactor efficiency, the space-time yield are the main performance criteria. This latter factor determines whether a process is economically or commercially viable since it can be used to compare performance of different electrode designs as well as comparing an electrochemical process with the space-time yields for alternate non-electrochemical technologies. 

Sodium Measurements. The sodium ion content was measured by two techniques 1) A Perkin-Elmer 403 atomic absorption unit was used to obtain the total amount of sodium in a particular solution and 2) an Orion 801 pH meter with Corning sodium-specific ion electrodes was used at 25 °C to determine the free sodium present. An attempt to measure the free sodium content at 60 °C failed because of thermal instability. It was especially important to determine if the sodium ions present were free so that correct molecular weights could be computed from the VPO data. The calibration was accomplished by dissolving small amounts of sodium benzoate in the DMF, or by using DMF-distilled water (3 + 1) mixtures containing dissolved NaOH. Both calibrations gave similar final results. Even though tap water was used in the synthesis, interference from other ions (e.g., Ag+, Li+, or NH4+) was considered minimal be-... 

As COR and OER occur simultaneously in the cathode, their kinetics are particularly important in evaluating carbon-support corrosion. The kinetics of OER is material-specific, dependent on catalyst composition and electrode fabrication.35,37 -39 A number of OER kinetics studies were done on Pt metal electrodes.37-39 However, there is a lack of OER kinetics data on electrodes made of Pt nano-particles dispersed on carbon supports. Figure 2 shows the measured OER current density with respect to the overpotential defined by Eq. (6).35 The 02 concentration was measured at the exit of a 50-cm2 cell using a gas chromatograph (GC). The 02 evolution rate (= 02 concentration x cathode flow rate) was then converted to the OER current density, assuming 4e /02 molecule. Diluted H2 (10%) and a thicker membrane (50 p,m) were used in the measurement to minimize H2 crossover from anode to cathode, because H2 would react with 02 evolved at the cathode and incur inaccuracy in the measured OER current density. Figure 2 indicates that the OER... 

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