Retention time shorten

Substantial individual differences were observed in the response to study breads and the ranges of enterolactone concentration changes in the groups were as follows -54.5-60.0 nmol/1 (placebo), -26.2-101.3 nmol/1 (LP), -19.6-81.8 nmol/1 (HP). This was something that could have been expected as in several studies dietary factors have explained only 10% of the variation in serum enterolactone (Vanharanta et al, 2002b Kilkkinen et al., 2001). This gives further support to the major role of intestinal bacteria in the synthesis of enterolactone. Decreased concentrations of enterolactone may occur due to an increased fiber intake, which may shorten the retention time in the colon and lead to incomplete metabolism of plant lignans. Constipation was earlier shown to be associated with an increased level of serum enterolactone (Kilkkinen et al., 2001). 

The presence of alcohol would increase the polarity of the mobile phase, so that solute retention times would be shortened. Also, we would not expect to get very good reproducibility, as the concentration of stabiliser will vary slightly from batch to batch. 

The temperature of the column affects both the vapor pressures of the mixture components and the solubilities of the mixture components in the stationary phase. Sometimes a low temperature separates some mixture components that are not separated at higher temperatures. However, the lower temperature may result in inordinately long retention times for other mixture components. Temperature programming allows the best of both worlds—complete separation of short-retention-time components at the low temperature, while shortening retention times of the others when the column temperature is raised later. 

The elution volumes of the fatty acid derivatives are affected principally by the number of carbon atoms and the number of unsaturated bonds in the fatty acid chains. In acetonitrile-water, unlike methanol-water, the number of unsaturated bonds seemed to be of greater importance. Also, the effect of the column temperature was important. A value of 30°C was used to shorten the analysis time, with good resolution. Thus, satisfactory resolution and favorable retention times (within 15 min) of the C 0 0-C22 6 fatty acid hydrazides were obtained in RP-HPLC with isocratic elution using acetonitrile-water (85 15), as shown in Fig. 5b. 

Mobile phases used in reversed-phase chromatography are frequently composed of mixtures of methanol and water or acetonitrile and water. Increasing the proportion of water causes an increased retention of the more hydrophobic solutes relative to the more polar solutes. The surface tension of the mobile phase plays a major role in governing solute retention, so an increase in temperature, by reducing viscosity, increases column efficiency and shortens retention times. 

Becker, K. Gas chromatographic determination of blood gases, an equilibration method with shortened retention time. Klin. Wochschr. 48, 464 (1970). — Z. Anal. Chem. 256, 150(1971). 

A flow chart of a long mix neutralization process is shown in Fig. 34.19. The recommended retention time for soybean oil in this system is 6 min and was shortened by a major improvement in caustic-oil retention mixers developed by the Alfa Laval Company, Tumba, Sweden, in the mid-1990s.103... 

Kirkland et al. [6,167,171] dealt with the programming of S-FFF in an analysis of particle size distribution. They also used time-delayed exponential decay programming of the centrifugal force intensity, which allowed them to linearize the dependence of retention time to a logarithm of solute dimensions. Moreover, the total analysis time was shortened without sacrificing the resolution. 

Derivative prep nation can be used to shorten or lengthen the retention time of a substimce and this csai be he l to remove the substimce peak away... 

Due to inadequate mixing by biogas, solid buildup at the bottom of the anaerobic pond poses another maintenance problem to the palm oil mills. Excessive solid buildup at the bottom of the ponds will reduce the effective digester capacity and consequently shorten the hydraulic retention time. Thus the treatment efficiency will be adversely affected. 

The Type IV CSPs are used with aqueous mobile phases that contain copper(II) sulfate (CS). The usual starting concentration of CS is 0.25 mM and retention times can be manipulated by increasing or decreasing the CS concentration an increase in CS concentration usually shortens retention, whereas a decrease has the opposite effect. Concentrations as low as 0.05 mM and as high as 20.0 mM have been used. 

The retention times of solutes slightly increased with increasing temperature in the range of 40.0-65.0°C. As the volatilities of the solutes were increased with an increase in the temperature (which is favorable to shorten the retention time), the density of the mobile phase decreases with the temperature, which is not favorable for eluting the solute. In the range of temperatures mentioned above, the second factor is dominant thus a lower temperature is desirable for the separation of quercetin and risetin. 

Shortening separator columns is generally not feasible because the alteration process causes the separation efficiency to slowly diminish with time. A resolution between two signals that is too high leads to unnecessarily long retention times. This can be prevented by choosing appropriate eluents and stationary phases, respectively. A drastic reduction in the retention time of an ion may be achieved in special circumstances by a separation on the shorter pre-column. 

Consider the practical significance of the above result. First, other things being equal, the greater P° is, the smaller Vg will be (Eqn. 22.7), and the shorter the retention time will be (Eqn. 22.2). P° increases with increasing temperature thus, retention time decreases as the temperature is increased. One can also shorten retention times by converting the solutes of interest into more volatile derivatives, thus increasing P°. For example, amino acids converted to the volatile ester-amides have smaller overall retention times than the amino acids themselves. 

Shortening the retention time by using one. or more of the methods listed below... 

---