Chromatographic measurements crystals

Webber et al. (43) investigated the use of the acetone extracts of various soots. Soots were obtained by burning several substances in air, collecting the black residue in acetone, then applying a thin film of soot on the crystal. The extract of chlorobenzoic acid soot provided the best coating, and was sensitive to H2S in the concentration rage 1-60 ppm. Attempts were made to characterize the reaction by gas chromatographic measurement of major components, elemental analysis and IR. However, there was not sufficient information either to determine the reaction mechanism or characterize the soot extract. 

Certain compounds, whether present in solution or in solid state (as molecular or ionic crystals) emit light when they are excited by photons in the visible or near ultraviolet domain of the spectrum. This phenomenon, called luminescence, is the basis of fluorimetry, a very selective and sensitive analysis technique. The corresponding measurements are made with fluorimeters or spectrofluorimeters and, for chromatographic applications, with fluorescence detectors. 

Mixing of 1 mmol of triazene 1-oxide 1 with 1 mmol of a- or -naphthol in acetone followed by evaporation gave the mixed crystals. These were finely ground in a mortar, spread on petri dishes and directly exposed to sunlight. TLC examination showed that the reactions were finished within 7-10 h. The temperature was measured as 18 to 25 °C. Chromatographic separation on silica gel with ethyl acetate-toluene (1 10) as eluent gave two zones. The first zone with the higher Rf value (at the start) afforded a multicomponent mixture, which could neither be separated nor could individual components be identified. 

The QCM sensors [5] have gained popularity because they are operated at room temperature and allow combinations of selective layers different to those of MOS, MOSFET and PC sensors. The QCM measures physical mass of the analyte by recording the change in frequency of a quartz crystal when the analyte binds to it. Layers of gas chromatographic stationary phases and natural or synthetic lipids can discriminate between alcoholic drinks, perfume and flavor odorants. 

The measurements with the CD s were performed on a Chrom 4 gas chromatograph with the flame-ionization detection (Laboratornl Pristroje, Prague, Czechoslovakia) The measurements with the liquid crystal phases were performed on a Perkin Elmer F-ll instrument with a flame-ionization detector ... 

More recently, a detailed study of diffusion of the xylene isomers in large crystals of NaX and natural faujasite was undertaken by both sorption rate and tracer exchange.(11-14) The data obtained by both these techniques using several different crystal sizes were entirely consistent but the diffusivities were much smaller than the values derived for the same systems by NMR PFG measurements. In an attempt to resolve this discrepancy we have developed a new chromatographic technique (zero length column or ZLC) which is less sensitive than conventional sorption methods to the intrusion of external heat and mass transfer resistances and which is therefore useful for following relatively rapid diffusion processes. The method has now been applied to study the diffusion of a range of different hydrocarbons in both A and X zeolite crystals and the results of these studies are summarized here. 

In the application of the chromatographic method to the measurement of intracrystalline diffusivity it is preferable to pack the column directly with unaggregated crystals rather than with composite (pelleted) material since this eliminates the possible intrusion of macropore resistance. The small crystal size of commercial zeolite samples presents a significant practical problem. Early attempts to utilize a column packed directly with such crys-... 

For sufficiently small particles 0 0 and 1, so the measured rate constant approaches the intrinsic rate constant (k). By making replicate measurements under similar conditions, with different particle size fractions it is possible to determine both the intrinsic rate constant and the effective interparticle diffusivity. Haag [67] suggested that this approach could be used to determine intracrystalline diffusivities in zeolite crystals. A more complete experimental study in which the diffusivity of 2,2-dimethyl butane in HZSM-5 was determined both chromatographically and from measurements of the cracking rate under diffusion-limited conditions was reported by Post et al. [68] - see Fig. 11. This approach has the advantage that it makes steady-state rather than transient measurements, but it is limited to sorbates for which a suitable catalytic reaction occurs. 

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