Pressure-jump apparatus with

A pressure perturbation results in the shifting of the equilibrium the return of the system to the original equilibrium state (i.e., the relaxation) is related to the rates of all elementary reaction steps. The relaxation time constant associated with the relaxation can be used to evaluate the mechanism of the reaction. During the shift in equilibrium (due to pressure-jump and relaxation) the composition of the solution changes and this change can be monitored, for example by conductivity. A description of the pressure-jump apparatus with conductivity detection and the method of data evaluation is given by Hayes and Leckie (1986). 

Kinetic experiments were conducted using a pressure-jump apparatus with conductivity detection. Details of the apparatus and its operation can be found in Appendix A. Sample equilibration time can have an effect on the kinetic results (e.g., slow processes (on the order of hours-days) occurring concurrently but not monitored in the time frame of the p-jump technique (milllseconds-seconds)) hence, it is important to run kinetic experiments on samples with similar equilibration history. All samples were equilibrated between 3 and 4 hours for the p-jump kinetic studies. The temperature of the p-jump apparatus, which includes sample and reference solution cells, was maintained at 25.0°C 0.1°C. 

Pressure-Jump Apparatus with Conductivity Detection... 

Goldsack, D. E., Hurst, R. E., and Love, J. (1969). A pressure jump apparatus with optical detection. Anal. Biochem. 28, 273-281. 

Sectional views of a pressure jump apparatus with optical absorption detection... 

A sudden pressure release or application of pressure can be employed to cause the pressure jump. Ljunggren and Lamm (1958) described the first pressure-jump apparatus, which consisted of a sample cell connected to a nitrogen tank. With this apparatus, a pressure increase to 15.2 MPa could be obtained in 50 ms by quickly opening the valve. Chemical relaxation was monitored conductometrically. 

In 1959 Strehlow and Becker developed a pressure-jump apparatus that enclosed a conductivity cell containing the reaction solution, and a reference cell under xylene in an autoclave. The reaction and reference solutions were pressurized to about 6.1 MPa with compressed air. By the blow of a steel needle, a thin metal disk used to close the autoclave was punctured and the pressure was released within about 60 s. 

Figure 4.3. Schematic diagram and sectional views of the autoclave of the pressure-jump apparatus of Knoche and Wiese (1974) 1, conductivity cells 2, potentiometer 3, 40-kHz generator for Wheatstone bridge 4, tunable capacitors 5, piezoelectric capacitor 6, thermistor 7, 10-turn helipot for tuning bridge 8, experimental chamber 9, pressure pump 10, rupture diaphragm 11, vacuum pump 12, pressure inlet 13, heat exchanger 14, bayonet socket. [From Knoche and Wiese (1974), with permission.]...

Figure 4.8. Schematic representation of the pressure-jump apparatus of Davis and Gut-freund (1976). The instrument is composed of the following components A, observation cell B, hydraulic chamber C, absorbancy photomultiplier D, thermostatted base E, quartz fiber optic from light source F, quartz pressure transducer for the triggering of data collection G. hydraulic pressure line H and I, observation cell filling and emptying ports J, fluorescence emission window K, bursting disc pressure-release valve L, mechanical pressure-release valve M, trigger mechanism N, reset mechanism O, value seat and P, phosphorbronze bursting disc. (Reprinted with permission of the publisher.)...

Using a pressure-jump apparatus the dissolution time for sodium dodecyl sulphate micelles has been measured in solutions which also contain polyvinyl pyrrolidone. The relaxation time associated with the association/dissolution of the micelles depends on the amount of polymer present and also its molecular weight. In addition the activation energy of the dissociation/ association process decreases in the presence of the polymer. These data suggest that the micelles are incorporated along the polymer chain and a simple mechanism for the dissolution of micelles on the polymer is proposed. 

These studies were undertaken using a pressure-jump apparatus over the time range 10-10 sec. incorporating a rapid data capture and analysis system. The polymer, polyvinylpyrrolidone, PVP, (Aldrich) was used without further purification. Sodium dodecyl sulphate, SDS, (Henkel) was chosen as the surfactant system, since a considerable wealth of equilibrium data were already available involving this surfactant. SDS was purified by repeated recrystallisation from two solvents until the relaxation time at the CMC agreed with literature values. 

Figure 2.4 Block diagram of the p-jump apparatus with conductivity detection and the twin cell arrangement from Dialog (Germany). A, autoclave Ci and C2, conductivity cells E, electrodes M, elastic membrane D, metal diaphragm P, pressure pump m, manometer G, 40 kHz generator driving the conductivity bridge Cg and C4, tunable capacitors and Rj, helipot resistances Rg, potentiometer Os, oscilloscope (now replaced by a computer).

Figure 4.5. Block diagram of pressure-jump relaxation apparatus with digitizing interface. [From Krizan and Strehlow (1974), with permission.]...

The first p-jump apparatus was developed by Ljunggren and Lamm (1958). A conductivity cell was filled with the solution of interest and then placed in an autoclave connected to a 15-MPa N tank. The stopcock was rapidly opened to create a rapid pressure increase. With this method, one could obtain a pressure change of 15 MPa in 0.05 s. Ljunggren and Lamm (1958) followed the relaxation time conductometrically. 

Two preliminary accounts have appeared which report new approaches to the problem of the mechanism of complex formation in water. The reaction between Nd " and S04 was investigated by ultrasonics in H2O and D2O and it was concluded from the fact that the reaction was 2.3 times slower in D2O than in HgO (whereas the dissociation step was accelerated) that solvent exchange at the metal ion cannot be the controlling step in lanthanoid complexation reactions. A high-pressure cell with spectrophotometric detection was used in conjimction with a laser temperature-jump apparatus to measure the volumes of activation of the reaction of Co + and Ni + with the bidentate ligand pyridine-2-azo-p-dimethylaniline (1), and of Ni + with NH3. In all cases the value of AV was ca. 8 cm mol, a value which corresponds to a considerable fraction of the molar volume of water ... 

---