Reference cell technique

The utilization of the photometric synthesis control [95] was already mentioned in Sect. 3.1.3, 3.2.4, and 3.3.6 (Fig. 61). The system consists of a two-channel flow photometer with reference cell technique operating on two wavelengths. It is connected to a continuous line recorder with fifteen times automatic scale expansion at constant sensitivity and a graphic integration supplement. The photometer reference flow cell of a wide inner diameter has an optical path of 5 mm. It is inserted between the metering system of the synthesizer and the centrifugal reactor and allows a flow rate of 5 to 10 liters/hour. 

Besides shear-induced phase transitions, Uquid-gas equilibria in confined phases have been extensively studied in recent years, both experimentally [149-155] and theoretically [156-163]. For example, using a volumetric technique, Thommes et al. [149,150] have measured the excess coverage T of SF in controlled pore glasses (CPG) as a function of T along subcritical isochoric paths in bulk SF. The experimental apparatus, fully described in Ref. 149, consists of a reference cell filled with pure SF and a sorption cell containing the adsorbent in thermodynamic equilibrium with bulk SF gas at a given initial temperature T,- of the fluid in both cells. The pressure P in the reference cell and the pressure difference AP between sorption and reference cell are measured. The density of (pure) SF at T, is calculated from P via an equation of state. 

In principle, different reference electrodes may be used if the cell is provided with a separate compartment and a Luggin capillary. But if the flow cell technique is to be applied, it is more convenient to avoid the use of capillaries where the solution cannot be easily exchanged. Active bulk components could diffuse through the capillary and give rise to erroneous responses. A small palladium gauze charged with hydrogen directly immersed in the solution can be used as the reference electrode (PdH ) [18]. 

Fig. 7.1 Spectrophotometric simultaneous non-competitive measurement of KIE. In this technique the reaction mixture containing the reference isotopomer is placed in the reference cell and the mixture with the other isotopomer in the sample cell (at identical concentrations). The two cells are placed in a common thermostat (www.chemguide.co.uk)...

The solid reference electrode technique is able to obtain almost the same results as the SO2 gas concentration cell method. The apparatus can be made more compact, simple and cheaper by using the solid reference electrode technique. The SO2 gas detection with solid reference electrode method is a promising technique for practical applications. 

This technique was first employed in GC by Boeke [1] and was later introduced to LC by Essigmann and Catsimpoolas [2]. The column eluent passes directly to the sample cell and thence to the reference cell by way of a short length of tubing, the volume of which is (Av). As the signal from the reference cell acts electrically in opposition to the signal from the sample cell, the output from the detector is (AX - AX ), as given in equation (1). Consequently, the output will provide the differential of the... 

While the technique of refractive index detection is less sensitive than UV or MS detection, it represents yet another useful, highly developed, quantitative online detector. RI detectors can perceive the difference in refractive index between a reference solvent and a solution with one or more analytes. Because of the comparative nature of the signal, a reference solution is necessary and gradient operations can be carried out only with very precise controllers to ensure that the reference cell and the sample cell have the same mobile-phase composition at any given time. 

A Setaram C80 differential microcalorimeter coupled to an evacuable glass gas-handling system was used to monitor ammonia adsorption and associated enthalpies of adsorption. Catalyst samples (ca. 150 mg dry weight) were conditioned in the calorimeter at 100 °C under vacuum for two hours, with an empty reference cell. Successive pulses of ammonia (ca. 0.06 mmol) were introduced to the sample at 100 °C. Enthalpy changes associated with each dose were converted to molar enthalpies of adsorption and are expressed as functions of resin coverage. Further details of the technique have been reported previously. ... 

The melting temperature of a-Si3N4 up to a pressure of 37 GPa was determined by diamond-anvil cell technique [122]. The melting temperature varied from 2200 75 K at 3.5 GPa to 3600 200 K at 37 GPa. The authors did not refer to a phase transition a-Si3N4/c-Si3N4. 

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