Elution rates

Consequently, as the inlet pressure increases, the mean flow rate will be reduced according to the pressure correction function and the expected decrease in elution rate will not be realized. Consider an open tubular column. 

Temperature programming was introduced in the early days of GC and is now a commonly practiced elution technique. It follows that the temperature programmer is an essential accessory to all contemporary gas chromatographs and also to many liquid chromatographs. The technique is used for the same reasons as flow programming, that is, to accelerate the elution rate of the late peaks that would otherwise take an inordinately long time to elute. The distribution coefficient of a solute is exponentially related to the reciprocal of the absolute temperature, and as the retention volume is directly related to the distribution coefficient, temperature will govern the elution rate of the solute. 

Measure a 1000 mL aliquot of sample solution and transfer to the top of the Cig SPE cartridge column which was conditioned with 5 mL of ethyl acetate, 5 mL of methanol and 10 mL of distilled water in advance at an elution rate of 10 mL min . After washing the column with 10 mL of distilled water, dry the column with suction for 30 min, then elute with 0.5 mL of acetone and then 5 mL of ethyl acetate. Dry the eluates using a rotary evaporator at 35 °C and by N2 purging. 

Indirect evidence of isotopic fractionation among different complexes was obtained by Marechal et al. (1999) and Marechal and Albarede (2002) who observed different elution rates of Cu and Cu on anion-exchange columns (Fig. 11). These experiments were confirmed by Zhu et al. (2002) and Rouxel (2002) with similar results on fractionation coefficients. Figure 11 shows that, in HCl medium, the heavier isotope 65 is less well retained on the column than the lighter isotope 63. Marechal and Albarede (2002) used an error function approximation to the elution curve to derive the ratio of fractionation coefficients for the 63 and 65 isotopes between the resin and the eluent. From the relationship between the elution volume (position... 

The target dipeptide product was purified on a SephadexG-10 column (16 mm x 1000 mm) equilibrated and eluted with water at the elution rate of 1.0 mL min . The elution process was monitored at 220 nm. The fractions collected were lyophihzed to afford the desired product (29.6 mg). The HPLC purity and the yield of the product were 93.5 % and 82.9 % respectively. 

The phenomenon of secondary exclusion is caused by the higher diffusion rate of the smaller polymer species compared with the larger ones. The smaller macromolecules may timely occupy the packing pores, which are otherwise accessible also for larger polymer species. Thus the elution rate of the large macromolecules is further accelerated. The term secondary exclusion was coined by Altgelt [102] and the theory of process was elaborated by Janca [103]. 

The applicability of LC LC to the (ultra) high-molar-mass polymers. Contrary to liquid chromatography under critical conditions, LC LC likely exhibits no upper limit of the sample molar mass [234]. On the other hand, if the difference in elution rates of the barrier forming small molecules and the oligomeric species is too small, the LC LC separation becomes insufficient. As a result, LC CC and LC LC may be considered mutually complementary from the point of view of their applicability in the... 

Control of elution rate of ionisable compounds by adjustment of the pH of the mobile phase... 

In some studies it is desirable to do constant infusion to achieve a steady state or equilibrium condition which is a function of input, extraction rate, tissue washout, and radioactive decay (23). Figure 6 shows the yield of Rb-82 at various elution rates to a steady-state condition. At the faster flow rate of 5.33 ml/min, there is 24% yield of Rb-82 and at the slower flow rate of 2.15 ml/min there is about 1% yield of Rb-82. The lower yield at the slower flow rate is mostly accounted for in decay during transit through the line to the patient. 

The short lived positron-emitter Rb-82 (t 1/2=1.26m) has potential application in cardiovascular diagnostic nuclear medicine. A generator system containing the parent Sr-82 has been developed that will provide an eluate of Rb-82 suitable for direct infusion. The Rb-82 is eluted by a syringe pump from a hydrous stannic oxide column in a continuous stream of physiological saline solution. The rate of elution (infusion) can be controlled from 10 to 100 ml/ min. At elution rates of 25, 50, and 75 ml/min,... 

For the application of a continuous perfusion system, it is necessary to know what elution rate to use under steady state conditions in order to minimize either the total volume of solution to be injected or the duration of the injection. The practical objective of a scintigraphic-examination is to accumulate, in a given organ, a sufficient radioactivity to produce good counting statistics. An analytical study of this problem brings us to the formulation of the following equation ... 

FigurB 25-26 Application of the method development triangle to the separation of seven aromatic compounds by HPLC. Column 0.46 x 25 cm Hypersil ODS (C)e on 5-(j.m silica) at ambient temperature ( 22°C). Elution rate was 1.0 mL/min with the following solvents (A) 30 vol% acetonitrile/70 vol% buffer (B) 40% methanol/60% buffer (C) 32% tetrahydrofuran/68% buffer. The aqueous buffer contained 25 mM KH2P04 plus 0.1 g/L NaN3 adjusted to pH 3.5 with HCI. Points D, E, and F are midway between the vertices (D) 15% acetonitrile/20% methanol/65% buffer (E) 15% acetonitrile/16% tetrahydrofuran/69% buffer (F) 20% methanol/16% tetrahydrofuran/64% buffer. Point G at the center of the triangle is an equal blend of A, B, and C with the composition 10% acetonitrile/13% methanol/11% tetrahydro-furan/66% buffer. The negative dip in C between peaks 3 and 1 is associated with the solvent front. Peak identities were tracked with a photodiode array ultraviolet spectrophotometer (1) benzyl alcohol (2) phenol (3) 3, 4 -dimethoxyacetophenone (4) m-dinitrobenzene (5) p-dinitrobenzene ...

The advantages of HPLC are the result of two major advances (1) the development of stationary supports with very small particle sizes and large surface areas, and (2) the improvement of elution rates by applying high pressure to the solvent flow. 

What are the experimental data underlying the first hypothesis It is common knowledge today that the covalently bound heparin (if bound to the polymer rigidly and inexorably) is usually less active than ionically attached heparin which is capable of elution. In a series of works a group of Japanese investigators, who are today probably the only supporters to this concept, has disclosed the correlation between thromboresistance of the polymer and the amount of heparin released into the bloodstream 68 71). The minimal elution rate of heparin providing sufficient thromboresistance was found to be 4 x 10s g/cm2 min. The decrease of the rate of elution resulted in a drastic decrease of thromboresistance. 

Both the free and the combined forms of phenolic acids in date fruit (Phoenix dactylifera L.) were analyzed by HPLC (19). The elution rate of phenolic acids increased with the degree of hydroxylation by isocratic elution using dioxane-acetic acid (15 85) on a /zBondapak C,8 column. Ferulic acid was the most abundant in the free form, and p-coumaric, vanillic, p-hydroxy-benzoic, protocatechuic, and syringic acid were also identified in dates. 

Let mp s and mp be the polymer mass of the considered P-mer in the sol and gel, respectively, cp s and cp the corresponding concentrations, u(P) = (dz/dt)p the constant elution rate of the P-mer transported along the z-axis of the vertical PDC-column, and v the mean overall linear rate of the column liquid then, a trivial integration of the chromatographic transport Equation (i.e. the thermodynamically and hydrodynamically defined retention coefficient)... 

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