Experimental Equipment and Analytical Methods

This chapter provides some essentials about the individual components and how they affect ozonation. First the material of the equipment necessary for containing ozone (B 2.1) is examined, followed by the equipment for producing it (B 2.2), and bringing the reactants together (B 2.3). Methods to measure ozone, with their advantages/disadvantages (B 2.4) and the safety aspects to consider (B 2.5) are then discussed. This is rounded off with a list of common questions, problems and pitfalls that we have come across over the years (B 2.6). Perhaps it will be helpful to read before starting your own experiments. 

---

The experimental setup, procedure and analysis are described in detail by Pfohl et al.11-12. For the systems containing acetone and 2-propanol, two different apparatuses have been used. Each apparatus (-1000 cm3, static-analytical method) is placed in a thermostated bath and equipped with sampling capillaries, thermocouples and high-precision pressure transducers. 

The SSC RE IPPE in cooperation with Sev RAO is conducting the work on implementation of analytical and experimental methods for determination of NS LMR SRP characteristics in Gremikha. The correlation method is assumed to be used. Within the framework of this cooperation the experimental equipment was manufactured and... 

Beiner et al. tested the collecting capacity of several metal compounds for some volatile sulfur substances. They noted high enrichment rates and good selectivity for silver sulfide. It was used in combination with membrane extraction, thermodesorption, and GC-MS to analyze sulfides, thiols, and tetrahydrothiophene from water samples. Detection limits down to the lower ng/1 range were achieved. The disadvantages of the method are the experimental equipment, the long analysis times, and displacement reactions between the matrix and analytes on the sorbent s surface. 

These techniques do not differ only in terms of accuracy and experimental effort. Their application is also limited by the availability of the required equipment. Not all methods are suitable for columns with low efficiency, because peak deformations will affect the isotherm parameters. The actual setup and experimental conditions should be as close as possible to the operating conditions for later production purposes. However, to save time and solutes, the column dimensions are usually only of smaller (analytical) scale, or semipreparative at maximum. Preparative chromatography requires typically the application of adsorbents, with larger particle sizes compared to analytical applications. In isotherm measurements temperature control is crucial, since adsorption may show significant temperature dependence. Sometimes the costs of solutes prohibit the use of methods that need larger amounts of samples. 

In the case of compxrsitional data, a lot of analytical techniques can be chosen. Analytical procedures based on these techniques are then selected to be aprplied to the samples. Selected analytical methods have to be fully validated and with an estimation of their uncertainty (Gonzalez Herrador, 2007) and carried out in Quality Assurance conditions (equipment within sp>ecifications, qualified staff, and documentation written as Standard Operational Procedures...). Measurements should be carried out at least duplicate and according to a given experimental design to ensure randomization and avoid systematic trends. 

In synthetic methods, a mixture of known composition is prepared and the phase equilibrium is observed subsequently in an equilibrium cell (the problem of analyzing fluid mixtures is replaced by the problem of synthesizing them). After known amounts of the components have been placed into an equilibrium cell, pressme and temperature are adjusted so that the mixture is homogeneous. Then temperature or pressure is varied until formation of a new phase is observed. This is the common way to observe cloud points in demixing polymer systems. No sampling is necessary. Therefore, the experimental equipment is often relatively simple and inexpensive. For multicomponent systems, experiments with synthetic methods yield less information than with analytical methods, because the tie lines carmot be determined without additional experiments. This is specially trae for polymer solutions where fractionation accompanies demixing. 

The active site responsible for the aerobic oxidation of alcohols over Pd/AljO, catalysts has long been debated [96-lOOj. Many reports claim that the active site for this catalyst material is the metallic palladium based on electrochemical studies of these catalysts [100, 101]. On the contrary, there are reports that claim that palladium oxide is the active site for the oxidation reaction and the metalhc palladium has a lesser catalytic activity [96,97). In this section, we present examples on how in situ XAS combined with other analytical techniques such as ATR-IR, DRIFTS, and mass spectroscopic methods have been used to study the nature of the actual active site for the supported palladium catalysts for the selective aerobic oxidation of benzylic alcohols. Initially, we present examples that claim that palladium in its metallic state is the active site for this selective aerobic oxidation, followed by some recent examples where researchers have reported that ojddic palladium is the active site for this reaction. Examples where in situ spectroscopic methods have been utilized to arrive at the conclusion are presented here. For this purpose, a spectroscopic reaction cell, acting as a continuous flow reactor, has been equipped with X-ray transparent windows and then charged with the catalyst material. A liquid pump is used to feed the reactants and solvent mixture into the reaction cell, which can be heated by an oven. The reaction was monitored by a transmission flow-through IR cell. A detailed description of the experimental setup and procedure can be found elsewhere [100]. Figure 12.10 shows the obtained XAS results as well as the online product analysis by FTIR for a Pd/AljOj catalyst during the aerobic oxidation of benzyl alcohol. 

In analytical practice, precision is often sub-divided into repeatability and reprodncibUity. Repeatability refers to the spread in values obtained on multiple repeats of the same analysis of the same sample, performed consecutively by the same operator using the same apparatus repeatability thus measures the degree of short term control of the analytical method. In contrast, the reproducibility of the analytical procedure refers to comparison of experimental estimates of repeatabUity obtained some time later by the same analyst using the same method and equipment, or perhaps in a different laboratory and/or by a different analyst using similar equipment on another aliquot of the same analytical sample or a similar sample thus defined, the experimental reproducibility clearly involves both random errors and possibly uncontrolled systematic errors (e.g., arising from temperature variations, differences in clean-up efficiency etc.). 

For multicomponent systems, experiments with synthetic methods yield less information than with analytical methods, because the tie lines cannot be determined without additional experiments. A common synthetic method for polymer solutions is the (P-T-m ) experiment. An equilibrium cell is charged with a known amount of polymer, evacuated and thermostated to the measuring temperature. Then flie low-molecular mass components (gas, fluid, solvent) are added and the pressure inereases. These eomponents dissolve into the (amorphous or molten) polymer and the pressure in the equilibrium eell deereases. Therefore, this method is sometimes called pressure-decay method. Pressure and temperature are registered after equilibration. No samples are taken. The composition of the liquid phase is often obtained by weighing and using the material balance. The synthetic method is particularly suitable for measurements near critical states. Simultaneous determination of PVT data is possible. Details of experimental equipment can be found in the original papers compiled for this book and will not be presented here. 

A description of the equipment, instruments, and apparatuses used to perform the work should be included in this section. Raw materials used, routine procedures employed, and glassware along with consumables utilized, may be simply listed. Quite often, neat schematic diagrams of equipment and instruments will greatly enhance the clarity of the written text. The experimental methods should be clearly described, with reference given to standard methods like those reported in analytical chemists handbooks. The aim is for the reader to understand fully how the raw data were collected. 

---