Eluent phase

The value of is dependent on the size of the population of molecules of component A in the stationary and eluent phases [1]. As the equilibrium is d3mamic, there is a continual, rapid interchange of molecules of component A between the two phases. The fraction of time, fm, that an average molecule of A spends in the mobile phase is given by ... 

Organic Stationary Eluent phase Comments Detection LD Ref. 

Table 7 gives levels of cocaine and benzoylecgonine for 5 hair samples (obtained from cocaine abusers). The supercritical phase extraction has been made under the same conditions as that for opiates (P = 25 MPa, T = 4°C, flow rate = 0.7 mL/min eluent phase C02/Me0H/TEA/H20 85/6/6/3 v v). 

The protected (S - S) (1-10) salmon calcitonin is purified by preparative chromatography on silica as stationary phase with a solvent mixture (dichoromethane / methanol / acetic acid (93 / 7 / 2 v / v / v)) as eluent phase. After precipitation with water the pure product is analysed by HPLC on Lichrospher 100 RP 18 (125 x 4 mm) 5 micron as stationary phase and with a mobile phase (methanol / water / N,N-dimethylformamide / trifluoracetic acid 70 / 30 / 5 / 0.4 v / v / v / v). The DMF is introduced in the eluent phase to solubilise the protected ( S - S) (1-10) salmon calcitonin. The HPLC profile of the pure protected (S - S) (1-10) salmon calcitonin is shown in Figure 8. 

Compound Sample Mode Sorbent Eluent Phase Rel... 

The installation allows a continuous production by chromatographic separation by simulating the displacement of the countercurrent bed of the eluent phase. This simulation is done by sequenced displacement of the injection points, from one column to another, upstream to the eluent phase. The time interval between two displacements is called the switching time. 

In chromatography, the retention factor, or, equivalently, the capacity factor, is used to characterize the chromatographic equilibrium properties of an analyte. The retention factor of an analyte, k, is usually derived to be the product of the column phase ratio, Vr/Ve, and the distribution coefficient of the analyte between the stationary phase and eluent phase, Ca,r/ca,e, eqn [24] ... 

For equilibrium [11], the most used quantitative relation of as a function of electrolyte salt concentration is based on the assumption of a Donnan potential in the resin phase, i.e., eqn [19] is assumed to be valid. It is also assumed that the concentration of co-ions to the surface charges is negligible in the resin phase so that cr.r is equal to the concentration of surface charges in the resin phase, Cr. This value is therefore constant and independent of the concentration of cb,e in the eluent phase. Combining eqn [19] with eqn [24] gives the following expression for the retention factor as a function of Cb,e ... 

The retention in SEC, in which the solute partition takes place between the common eluent phases in two different environments, interstitial and pore space, is expressed is follows ... 

Table 6.8 shows some adsorbents used to prepare the stationary phase in the chromatographic separation of carotenoids by TLC. The choice between them depends on the solvent or mixture of solvents to be used as eluent phase. The adsorbent layer is placed on the glass plate (normally 20 X 20 cm) as a slurry, with a thickness that is variable but small (0.2-0.7 mm). The adsorbent is allowed to air-dry and is activated in the oven at 110°C. The pigment extract is applied to the base of the plate, and the plate is put into a tank containing the eluent. Development is usually carried out upwards, and when complete, the band or bands of interest are selected, scraped off, and eluted from the silica with either diethyl ether (in the case of polar carotenoids) or acetone or ethanol (if the polarity is medium), and filtered to remove the sihca. 

The eluent phase concentration of species i on the th plate, C(2 , is linearly related to the adsorhent-phase concentration Cn hy... 

There are a number of phase equilibrium driven separation processes where the separation devices are such that crossflow of two bulk phases exists. Crossflow is utilized to enable continuous contacting between two immiscible phases, vapor and liquid, in an efficient fashion, as in a plate located in a distillation column. In chromatographic processes, crossflow of the solid adsorbent particles and the mobile fluid phase (liquid or gas) can lead to continuous separation of a multicomponent feed mixture introduced at one location of the mobile fluid (eluent) phase. We will illustrate first how crossflow of adsorbent particles or the adsorbent bed and the mobile fluid phase overcomes the batch nature of multicomponent separation in elution chromatography. Then we will focus on the cross-flow plate in a distillation column. 

We learned in Section 7.1 that adsorption processes carried out in fixed adsorbent beds are unsteady state processes. When injected with a multicomponent sample and fed continuously with an eluent or a carrier gas, the chromatographic process (Section 7.1.5) separates various species however, it is a batch process and separates the sample injected. If one could carry out continuously the separation of a multicomponent feed mixture via adsorption in one vessel, it would be quite useful. Continuous separation via adsorption must satisfy the following criteria. (1) The adsorbent has to be regenerated. (2) The adsorbent must not suffer attritional losses encountered if the bed of particles moves. (3) Each constituent of the feed must appear as a separate product stream such a goal has been achieved in devices having a crossflow of the adsorbent phase and the mobile/carrier/ feed/eluent phase. 

---