Pulse chromatography

The sample valve must be made so that it can be activated automatically at the command of the switching code. Also, in terms of hardware design, CC demands a reliable sample switch which must switch many more times over a given analysis cycle than it would have to if run in the single pulse chromatography mode. Since the sampling valve is probably the most unreliable component... 

Alumina Adsorption of aliphatic amines by means of pulse chromatography and temperature-programmed desorption. 74... 

Mobile fluid interaction with the stationary phase in SFC was investigated with mass spectrometric tracer pulse chromatography (96). Using capillary supercritical fluid chromatography, the effect of methanol as an additive was studied on the partition behavior of n-pentane into 5 % phenylmethylsilicone stationary phase. The results showed that the mobile fluid uptake by the stationary phase decreased with increasing temperature and pressure. Thus suggests that stationary phase swelling, may occur in SFC. 

Harlicl PJ.E. and Tezel, F.H., A Novel Solution Method for Interpreting Binary Adsorption Isotherms from Concentration Pulse Chromatography Data , Adsorption, 6 (2000), pp.293-309... 

Analyte Competition on Polyimide Adsorbents Studied by Deuterated Tracer Pulse Chromatography... 

Deuterated tracer pulse chromatography (TPC) was used to characterize the retention behavior of Tenax-GC and four polyimide-based sorbent materials. Deuterated n-hexane, ethanol, 2-butanone, nltromethane, and benzene were used as compounds to probe ive types o chemical Interactions o the compounds with the polymers. Retention properties were Investigated with dry and humidified helium carriers both with and without the Incorporation of non-deuterated test compounds. Analyte competition was shown to occur on all of the sorbents. Humidity affected the retention of the probe compounds on the polyimides to a much greater extent than on Tenax-GC. The technique was shown to elucidate subtle differences In sorbent behavior. 

Figure 2. Schematic Description of Dynamic Tracer Pulse Chromatography. Arrows at t=0 and t2 indicate injections of deuterated "pulse" compounds. The additional arrow in B indicates the initiation of the organic front.

Concentration pulse chromatography (also called elution on a plateau, step and pulse method, system peak method, or perturbation chromatography) is experimentally much simpler [100,103,104]. The same experimental procedure is used as for the determination of smgle-component isotherms. First, the column is equilibrated with a solution of the multicomponent mixture of interest in the mobile phase. When the eluent has reached the composition of the feed to the column, a small pulse of the pure mobile phase (vacancy) or of a solution having a composition different from that of the plateau concentration (see end of this section) is... 

SHAH Binary Sorption Equilibria by Pulse Chromatography 415... 

The kinetic characteristics are determined in GC methods both directly and indirectly. In direct pulse chromatographic methods the reaction rate can be established by the direct determination of the amount (concentration) of the reacting component, whereas in indirect methods this is done on the basis of the variations with time of the chromatographic properties of the reacting system, which are usually determined from the relationship between and the retention times of the non-reacting components and the composition of the reaction mixture used as the stationary phase [58]. Pulse chromatography... 

Tracer-pulse chromatography has been used to measure gas-solid phase equilibria. It allows the accurate measurement of sorption isotherms even at elevated temperatures and with multicomponent systems (37). 

The effective diifusivity measurement of gases by tracer-pulse chromatography in porous solids has been extended to include zeolites [faujasites, mordenites, 3A and 5A molecular sieves (35)]. The measured diffusions in this case were a strong function of molecular size. 

Earlier treatments of the tracer-pulse chromatography technique can be found in Helfferich and Peterson (39, 40). 

Recently the radioactive tracer pulse chromatography was used by Barrere and Deans to investigate the absorption reaction of CO2 in liquid diethanolamine (4J). One of the significant contributions to the field of adsorption rate measurement by chromatographic techniques can be found in a recent paper by Padberg and Smith (4Ia). 

Finally, the concentration pulse chromatography will be shortly discussed. A pulse of a sample is injected into a carrier gas flow which is passed through an adsorbent-packed column. The response of the column is measured as concentration c(/) vs. time t. The mean retention time r of the sample is experimentally determined. With the superficial velocity w, the bed length L, and the adsorbent density, the modeling leads to the following equation for the Henry coefficient He ... 

Hyun, S.H., and Danner, R.P., Adsorption equilibrium constants and intraparticle diffusivities in molecular sieves by tracer-pulse chromatography, AlChE J., 31(7), 1077-1085 (1985). 

The adsorption studies are achieved to measure the Henry constant at low partial pressure for toluene for temperature ranging from 175 to 350°C with the pulse chromatography technique [9]. From these results, the adsorption enthalpy AH is determined using Eq. 1. 

Adsorption studies were achieved on FAU zeolites by the determination of Henry constants for toluene for temperature ranging from 225 to 400°C using the pulse chromatography technique [5]. The Van t Hoff law (Eq. 1) was used to determine the adsorption energy. 

IGC measurements can be carried out using a pulse or continuous technique. The pulse of probe molecule is introduced into the carrier gas stream. This pulse is transported by the carrier gas through the system to the column with the solid sample. On the stationary phase, adsorption and desorption occur and the result is a peak in the chromatogram. The ratio of adsorption/desorption is governed by the partition coefficient. At fixed conditions of temperature and flow rate, the time of retention of a compound is characteristic of the system. An alternative is the fi ontal technique. This is carried out by injection into the carrier gas stream of a continuous stream of the probe molecule. When the sample enters into the column, there is a distribution between phases, and the concentration profiles takes the shape of a plateau, preceded by a breakthrough curve. The shape of this curve is characteristic of each system [3]. The benefit of the frontal technique is that equilibrium can be always established due to its continuous nature while pulse chromatography requires the assumption of a fast equilibration of the probe molecule adsorption on the surface. Between both techniques, the main part of publications describes pulse experiences, since they are faster, easier to control and more accurate, especially if interactions between probe molecules and the adsorbent are weak. 

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