Gas titration device

The semi-automatic gas titration device is a useful tool for measuring the rate, as well as the extent, of a gas consuming reaction. In terms of measuring the rate, or completeness, of a gas consuming reaction, this device is a versatile, precise, semi-automatic, time saving tool far exceeding the capabilities of a mercury manometer equipped with a meter stick. 

In principle, the semi-automatic gas titration device works by monitoring the partial vacuum created by a chemical reaction that consumes a gaseous substrate within a closed system.. 2 As the reaction progresses, the consumed gas is continually replenished in small uniform aliquots through a parallel set of solenoids connected to the reaction vessel and to a source of fresh reactant gas. 

Figure 1. Schematic of the semi-automatic gas titration device, depicting the arrangement of the electronic manometer, solenoids, and manifold.

Figure 3. Additional components of the semiautomatic gas titration device, (a) Ballast tank used for adjusting and maintaining the pressure during a reaction. Continued on next page.

A general schematic of the titration device is shown in Figure 1. The partial vacuum created by the gas consuming reaction is used to move mercury between two platinum electrodes in an electronically modified mercury manometer. When the mercury level has fallen from the top electrode, El, to just below the second electrode, E2, a process cycle controller activates the solenoids, B1 and B2. This solenoid action temporarily closes off the manometer to the reaction vessel and opens it to a source of reactant gas. Consequently, the loss in pressure is compensated by the introduction of fresh reactant gas to the manometer. The pressurization of the manometer forces the mercury level from below E2 back up to El. When the mercury level reaches El, the process cycle controller deactivates the solenoids. The... 

As a control experiment it is useful to calibrate the titration device with a well documented hydrogenation reaction. In this way the amount of hydrogen per refill aliquot can be determined. This gives the experimentalist an idea of the number of aliquots of reactant gas a particular reaction will theoretically consume. 

Early gas titrations based on soUd electrolyte devices for end point detection were carried out by Mobius [1], using air as the gaseous titrant and a potentiometric ceU made of stabilized zirconia for the end point detection. The setup is schematically outlined in Fig. 1. 

One of the first gas titrations by pumping ions through SE was carried out by Yuan and Kroger [2], who utilized stabilized zirconia as an oxygen pump. This device was combined later by UUmann et al. with a potentiometric cell and applied inter alia for safety monitoring in nuclear... 

The instrumentation became increasingly sophisticated with the addition of provision to heat the column, an automatic titrating device and then the first successful sensitive and universal detector, the gas-density balance, all of which required to be handcrafted [597]. In a companion paper to the description of the detector, the technique was demonstrated with the first separations of methyl ester derivatives of fatty acids [433]. It appears that the initial contact with the problem of the resolution of fatty acids must have inspired James to continue with the study of lipids, and in 1957 he independently published a paper on the determination of the structures of longer-chain fatty acids using gas chromatography and microchemical methods [434]. He subsequently went on to a distinguished career in lipid biochemistry. 

Air passing through the NO pathway enters the reaction chamber, where the NO present reacts with the ozone. The light produced is measured by the photomultiplier tube and converted to an NO concentration. The NO2 in the air stream in this pathway is unchanged. In the NO pathway, the NO- and N02-laden air enters the converter, where the NO2 is reduced to form NO all of the NO exits the converter as NO and enters the reaction chamber. The NO reacts with O3 and the output signal is the total NO concentration. The NO2 concentration in the original air stream is the difference between NO and NO. Calibration techniques use gas-phase titration of an NO standard with O3 or an NOj permeation device. 

A typical arrangement of components in a tensimetric titration is presented in Fig. 9.5, which shows the previously discussed tensimeter and a calibrated bulb attached to a vacuum line.2 The sample container on the tensimeter is fitted with a small reciprocating stirrer which consists of a thin glass rod connected to a glass-encased headless nail or glass-encased bundle of soft iron wire. This stirrer is driven by an external solenoid, the field of which is switched on and off by a current-interrupting device, the details of which are laid out in Fig 9.6. The size of the calibrated bulb is chosen so that it will contain the desired amount of gas for each addition at a pressure which is convenient and accurately measured (e.g., 100-500 torr). The calibration procedure and steps used dispensing gas from such a bulb are described in Section 5.3.G. 

The instrument can also be described further in terms of technical characteristics that are self-explanatory to the specialist. Examples are the titration calorimeter, bomb calorimeter, gas calorimeter, fiow calorimeter, drop calorimeter, heat flow calorimeter, and ice calorimeter. The designation microcalorimeter should be avoided because it does not show whether the term micro refers to the size of the device, the sample container, or the quantity of heat measured. 

Commercial titration calorimeter equipped with an injection device for the study of liquid/liquid reactions, such as those marketed by TA Instruments (USA) and the associated company Thermometric (Sweden), CSC (USA), Microcal (USA) or Setaram (France). For a student experiment, simpler systems based on Dewar flasks, such as those used by Brown et al. [9, 10], Arnett et al. [11] and Sherry and Purcell [12], may also be used. The calorimetric cell should be thoroughly dried by flushing with a dry gas such as nitrogen or argon. The blanket of inert gas also avoids contact with atmospheric humidity and oxygen. 

---