Conductivity meter cell

The conductivity meter cell is subjected to an alternating current. The frequency is set at 1 kHz for the standardized solution (KCl = 0.02 m) and wine, to avoid polarizing the electrodes. A conductivity meter is used for continuous monitoring of tartrate precipitation in wine (see Section 1.6.4, Figure 1.16). 

See 2-3.1. Typical laboratory conductivity meters have insufficient sensitivity to measure semiconductive and nonconductive liquids, in Appendix B, some tabulated conductivities appear as < suggesting that the instmment used was inappropriate. Some liquids listed as conductive might fall instead into the semiconductive category (e.g., cymene). Eor conductivities less than 100 pS/m especially, highly sensitive picoammeters are required to measure the small currents involved and great care is needed to avoid contamination of both the sample and the test cell. Several ASTM methods are available according to the conductivity range involved [143-146]. 

As already indicated conductimetric measurements are normally made with alternating current of frequency 103Hz, and this leads to the existence of capacitance as well as resistance in the conductivity cell. If the frequency of the current is increased further to 106 — 107 Hz, the capacitance effect becomes even more marked, and the normal conductivity meter is no longer suitable for measuring the conductance. 

Figure 10 Separation of monochloroacetate, dichloroacetate, and trichloroacetate on a sulfonated poly(styrene-divinyl benzene) column with suppressed conductivity detection. Column 2% cross-linked sulfonated poly(styrene-divinyl benzene) capacity 0.02 meq/g. Flow rate 64 ml/hr. Eluant 15 mM sodium phenate. Suppressor 0.28 x 25 cm Dowex 50W X8 column (200-400 mesh). Detector Chromatronix conductivity cell connected to a Dow conductivity meter. (Reprinted with permission from Small, H., Stevens, T. S., and Bauman, W. C., Anal. Chem., 47,1801,1975. 1975 Analytical Chemistry.)...

The conductance of a solution is the inverse of its resistance, and conductance has units of ohms 1 or mohs. The higher the conductance of a solution, the lower is its electrical resistance. A conductivity meter and conductivity cell are used to determine the effective resistance of a solution. The conductivity cell consists of a pair of platinized platinum electrodes with an area of approximately 1.0 cm2 with spacers designed to hold the electrodes rigidly parallel and at a fixed distance from each other. The cell can be standardized with solutions of known conductivity to obtain the cell constant, k so that the instrument response R... 

Figure 8. Diffusive permeability measurement system (1) thermostated bath (2) diffusion cell (3) membrane (4) thermometer (5) stirrer (6) circulation pump (7) conductivity cell (8) conductivity meter (9) recorder.

Analyses were done on a Dionex Model 14 Ion Chromatograph (IC), equipped with a Waters WISP 7 autosampler, Linear recorder, and interfaced with a Hewlett-Packard 3354 Laboratory Automated System. The principal components of the IC, shown in Figure 2, are (A) eluent reservoir, (B) pump, (C) injection valve, (D) separator column, (E) suppressor column, (F) conductivity cell, and (G) conductance meter with a recorder (integrator). 

Conductivity Meter. A second system utilizes a simple ohmmeter circuit, shown in Fig. 3. A meter, transformer secondary winding, and conductivity cell are connected in series so that the current is a function of the cell conductance. The meter may be calibrated in resistivity or conductivity units. 

Flow-through conductivity sensors suitable for insertion in pipelines (see Fig. 6.47a) are now available for use at temperatures up to 480 K. and pressures up to 1700 kN/m2(64). As conductivity is temperature sensitive, a thermistor is usually included in the detector circuit as part of a temperature compensator. Screw-in cells (Fig. 6.476) will withstand higher pressures. More recently, electrodeless methods of measuring conductivity have become available. In this case the solution is placed between two energised toroids. The output voltage of the instrument (from the output toroid circuit) is proportional to the conductivity of the solution provided that the input voltage remains constant. This type of conductivity meter can be used under much more severe conditions, e.g. with highly corrosive or dirty systems 43 . 

The timescale over which the conductance of the medium changes is a fundamental issue standard conductivity cells are designed for use with alternating current (AC), but the period of this current imposes a limit on rates of reactions that can be followed. To investigate reactions faster than the AC conductivity cell can handle, it is necessary to build and calibrate appropriate direct current (DC) conductivity cells, which is not a routine business. Conductivity meters that record continuously are uncommon. Nowadays, however, it is easy to interface a simple apparatus to a computer and collect the data with ad hoc software. 

Bult and Klasen (4) have performed conductivity measurements of silver sulfadiazine with a Radiometer conductivity meter, type CDM dj and conductivity cell, type CDC 104. 

SEC is measured with a conductivity meter, which normally consists of an AC bridge and a conductivity cell or electrodes. The conductance is measured between two electrodes. Two solutions of known conductivity should be used, one to calibrate the metre and the other to check the slope. It is important to correct all data for water temperature, either by calculation or by automatically using the metre s auto-temperature correction mode, since SEC is highly dependent on temperature. SEC increases by about 2% per degree centigrade rise in temperature due principally to an increase in water viscosity. 

The foam is produced in a foam generator. After filling cup 2 with the foam the measuring cell is closed with lid 5 so that the porous plate is in contact with the foam. The foam electrical resistance is measured with platinum electrodes connected to a conductivity meter. 

The solution conductivity was measured using a Yellow Springs Instrument conductivity meter (YSI Model 34) with a high pressure conductivity cell (cell constant of 0.0044 cm ). The high pressure cell consisted of ten stacked, stainless steel disc electrodes (10-mm diameter discs), insulated with Teflon washers. The meter is particularly well suited for use with this type of cell because capacitance errors are minimized by the active circuit and electrode over-potential is eliminated by measurement potentials of less than 1 volt. 

Solution pH was measured with a Ross combination electrode and Orion model 601A pH meter. Specific conductance was measured with a Yellow Springs Instruments model 32 conductance meter and cell. Cations were determined by inductively coupled atomic-emission spectroscopy. Sulfate and chloride were determined by ion chromatography. Bicarbonate was determined by titration with H2SO4 to pH 4.5. 

The specific conductance (L or K) or conductivity of a solution is always obtained by measuring the resistance (R) of the solution taken in a suitable container of known dimensions called conductivity cell, the cell constant of which has been determined by calibration with a solution of accurately known conductivity e g. a standard KCl solution. The instrument used for electrical conductivity measurement is known as conductivity bridge. A typical system consists of an alternating current (A.C.) Wheatstone bridge, a primary element of conductivity cell and a null balance indicator (as in solubridge ) or an electronic eye as in the conductivity meter. 

FIG. 3 Setup for the measurements of the swelling ratio (a) image analyzer (b) CCD camera (c) microscope (d) thermometer (e) measuring cell (f) pH meter (g) conductivity meter (h) aqueous phase supply system (APSS) (i) temperature control system (TCS). (From Ref. 27.)... 

Measurement of chemical parameters is best accomplished with an in-line closed measurement cell (25). When the values of the indicator parameters are observed to vary less than +10% over three consecutive well-bore storage volumes, the well may be presumed to have been adequately flushed for representative sampling. When in-line measurement cells are not practical, standard pH and conductivity meters and thermometers are used. 

S.5.5 Conductivity detectors. Many HPLC applications involve the separation of mixtures of ionic compounds. Consequently a continuous record of the electrical conductivity of the effluent can be used to detect the eluting species. Commercial conductivity meters with flow-cells of approximately 1 pi are available for the monitoring of inorganic ions, e.g. Na, NH4 and K also anions, halides, NOJ and SO . The HPLC cell is a scaled down version of the normal laboratory conductivity cell and consists of a pair of electrodes mounted in a low volume PTFE flow-cell. 

Experience demonstrated that in order to have a good agreement between experimental and calculated data, the value of the electrolyte conductivity is very important. Conductivities taken from literature as well as those measured with a standard conductivity meter (with frequencies 50, 250, 1000 and 4-000 Hz (Tacussel CD6N)) gave bad agreement. Therefore we made impedance measurements with a frequency sweep from 50 Hz to 10 kHz for the solution as well as a standard 0.1 N KCl solution, the latter being used to determine the cell constant. The obtained result for the copper- sulphate solution is represented in fig. 3.31. 

We measured electrical conductivity with a Radiometer CDM 83 conductivity meter and conductivity cell. 

Ammonium is determined in many laboratories in a CF system in which the Berthelot reaction is implemented. In the Berthelot reaction, ammonium reacts with chlorine and phenol in the presence of sodium nitroprusside as catalyst in alkaline medium. EDTA is added to prevent interference of calcium and magnesium. Modern systems have been developed that use macroporous polytetrafluoroethylene (PTFE) membranes. In these systems a sample is introduced into a stream to which sodium hydroxide solution is added. Ammonia diffuses through the PTFE membrane into a stream of de-ionized water and the stream is fed through the flow-through cell of a conductivity meter. In this system a minimum of reagents is required and the only interference is from volatile amines. 

GLOBAL conductivity meter (model DCM 900) and dip cell (oeU constant 1.0 cm-i) was employed to perform the conductivity measurements at different temperatures (viz., 293.15, 303.15, 313.15 and 323.15 K). The stock solutions of IMP (with or without a fixed concentration of KCl) were prepared in double distilled water. The conductivity was measured by successive addition of concentrated solution in pntre water (in case of without KCl) or in a fixed concentration of KCl solutions. A break in the specific conductivity versus drug concentration curve signals the onset of the micellization process (Figure 2). 

A prototype device of the conductivity and velocity (C-V) technique has been developed. The device mainly consists of three units, including a sample cell, a measurement unit, and a personal computer. The sample cell is made of stainless steel for aqueous samples under examination. The measurement unit is equipped with a conductivity meter with a 4-pole conductivity probe, an ultrasonic pulser/receiver with two ultrasonic transducers that are mounted on the two opposite sides of the sample cell. The measured electrical conductivity and temperature (by the conductivity meter) and the acoustic velocity (by the pulser/receiver) are acquired and sent to the computer by a high-speed data acquisition card. Specific software is developed and installed in the computer. The software is capable of determining salt and inhibitor concentrations using the measured conductivity, velocity, and temperature. By integration with a thermodynamic model HWHYD, the software can also determine the hydrate phase boundary, hence the hydrate safety margin given the hydrocarbon composition and the pipeline conditions. 

Figure 3. PVC degradation measuring apparatus, a. rotameter, b. degradation vessel with PVC sample, c. thermostat (180°C), d. conductivity cell (2B°C), e. conductivity-meter, f. computer.

A conductivity meter (Chapter 19) consists of two platinum electrodes bonded into the glass walls of the cells. The cell is placed into a solution and the electrodes are connected to a conductivity meter which connects an alternating voltage to the cell and measures the resistance of the solution between the electrodes. 

Conductance was measured using an Iskra conductivity meter MA 5964 (Iskra, Slovenia) with a homemade conductivity cell with cell constant of 0.7265cm. Conductivity and surface tension measurements require large amount of samples and for this reason these measurements were carried out during titration of the starting mixtures with water or IPM. 

In order to measure the conductance of a solution, a conductance cell is used. It has two electrodes, often platinum, coated with platinum black, separated by a fixed distance. Connecting these to a conductance meter, or more simply to a Wheatstone bridge, the conductance may be measured directly. In order to prevent electrolysis (see Topics C2, C9) taking place, which would change the concentrations in the solution, the bridge uses alternating current. Plastic and flow-through conductance cells are also available... 

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