Phase ratio

In addition to the nature of the carrier gas, column efficiency and ultimately, the resolution and sample capacity of a capillary column are affected by the physical nature of the column namely, the inner diameter and film thickness of the stationary phase. An examination of the distribution coefficient Kd as a function of chromatographic parameters is helpful here. Kj) is constant for a given solute-stationary phase pair and is dependent only on column temperature. Kd may be defined as 

TABLE 3.11 Selected Phase Ratios as a Function of Column Inner Diameter and Film Thickness 

Inner Diameter (mm) Film Thickness (pm) Capacity (ng/component) 

The coating efficiency, also called the utilization of theoretical efficiency (UTE), is the ratio of the actual efficiency of a capillary column to its theoretical maximum possible efficiency. Coating efficiency or UTE is expressed as 

---

It is important to stress that unnecessary thermodynamic function evaluations must be avoided in equilibrium separation calculations. Thus, for example, in an adiabatic vapor-liquid flash, no attempt should be made iteratively to correct compositions (and K s) at current estimates of T and a before proceeding with the Newton-Raphson iteration. Similarly, in liquid-liquid separations, iterations on phase compositions at the current estimate of phase ratio (a)r or at some estimate of the conjugate phase composition, are almost always counterproductive. Each thermodynamic function evaluation (set of K ) should be used to improve estimates of all variables in the system. 

The temperature and composition of each feed stream and the stream ratios are specified along with a common feed pressure (significant only for the vapor stream) and the flash pressure. For an isothermal flash the flash temperature is also specified. Resulting vapor and liquid compositions, phase ratios, vaporization equilibrium ratios, and, for an adiabatic flash, flash temperature are returned. 

Liquid phase compositions and phase ratios are calculated by Newton-Raphson iteration for given K values obtained from LILIK. K values are corrected by a linearly accelerated iteration over the phase compositions until a solution is obtained or until it is determined that calculations are too near the plait point for resolution. 

Uranium is subsequendy stripped reductively from the loaded solvent using a bleed stream of the raffinate acid to which ferrous iron has been added to reduce uranium to its nonextractable, quadravalent state. Raffinate is acid from which uranium has already been extracted. By controlling the organic-to-aqueous volume phase ratios in the extraction and stripping circuits, uranium is concentrated by a factor of approximately 70. 

The type of emulsion (o/w or w/o) is deterrnined by the volume ratio of the two Hquids provided the ratio is sufficiently high. For example, with 5% water and 95% oil (an o/w phase ratio of 19), the emulsion will become w/o unless extreme measures are taken to ensure the formation of an o/w emulsion. 

An eluted solute was originally identified from its corrected retention volume which was calculated from its corrected retention time. It follows that the accuracy of the measurement depended on the measurement and constancy of the mobile phase flow rate. To eliminate the errors involved in flow rate measurement, particularly for mobile phases that were compressible, the capacity ratio of a solute (k ) was introduced. The capacity ratio of a solute is defined as the ratio of its distribution coefficient to the phase ratio (a) of the column, where... 

It is clear that the separation ratio is simply the ratio of the distribution coefficients of the two solutes, which only depend on the operating temperature and the nature of the two phases. More importantly, they are independent of the mobile phase flow rate and the phase ratio of the column. This means, for example, that the same separation ratios will be obtained for two solutes chromatographed on either a packed column or a capillary column, providing the temperature is the same and the same phase system is employed. This does, however, assume that there are no exclusion effects from the support or stationary phase. If the support or stationary phase is porous, as, for example, silica gel or silica gel based materials, and a pair of solutes differ in size, then the stationary phase available to one solute may not be available to the other. In which case, unless both stationary phases have exactly the same pore distribution, if separated on another column, the separation ratios may not be the same, even if the same phase system and temperature are employed. This will become more evident when the measurement of dead volume is discussed and the importance of pore distribution is considered. 

Phase ratio focusing is based on the higher migration speed of components through the retention gap compared to that through the analytical column. Reconcentration depends on the ratio between the retention power in the pre- and in... 

The flowsheet in Figure 6 is somewhat analogous to that proposed and tested by Mclsaac, Baker, Krupa, LaPointe, Meikrantz, and Schroeder C3) for processing HLLW from LWR using DHDECMP. The major differences are the larger phase ratios in the extraction... 

An alternative measurement, the separation ratio (a), was proposed to eliminate the effect of different phase ratios and different flow rates... 

It is seen that the separation ratio is independent of the phase ratios of the two columns and the flow rates employed. It follows that the separation ratio of a solute can be used more reliably as a means of solute identification. Again, if the data is being processed by a computer, the corrected retention times will be used to calculate the separation ratios. In practice, a standard substance is often added to a mixture and the separation ratio of the substance of interest to the standard is used for identification. 

In the biocatalytic system, a second organic phase consisting of bis(2-ethyUiexyl)phthalate and containing the substrate is added at a phase ratio of 1 1. This procedure enables in situ product extraction and protects the microbial cells from toxic effects of the substrate and... 

In partition chromatographic systems, the selectivity and degree of retention are mainly determined by the compositions of the liquid stationary and mobile phases and by the phase ratio of these two liquids. 

In fact, the solute retention depends on the solubihty parameters of the solute, 8 , of the mobile phase, 8 , of the stationary phase, 8, and of the phase ratio given by Equation 4.7 [24] ... 

The determination of log Poa is far from being trivial whether potentiometric, shake-flask, chromatographic or other techniques are used and, often, this value is derived from the back-calculation discussed above, using logDj and pKj, which of course has to be known. This is often done in shake-flask determinations so that there is appreciable aqueous solubility (and thus partition) in the aqueous phase for highly Hpophilic drugs and it may also be accompanied by a variahon of the phase ratio, in favor of the phase where the compound is expected to be less soluble, to avoid saturation phenomena. 

The change in the apparent plQ (poKJ with varying water/organic phase ratios is an effective way to characterize ion-pair extraction (Fig. 16.1). 

However, as stated above, the partition coefficients measured by the shake-flask method or by potenhometric titration can be influenced by the potenhal difference between the two phases, and are therefore apparent values which depend on the experimental condihons (phase volume ratio, nature and concentrahons of all ions in the solutions). In particular, it has been shown that the difference between the apparent and the standard log Pi depends on the phase volume raho and that this relationship itself depends on the lipophilicity of the ion [80]. In theory, the most relevant case for in vivo extrapolation is when V /V 1 as it corresponds to the phase ratio encountered by a drug as it distributes within the body. The measurement of apparent log Pi values does not allow to differentiate between ion-pairing effect and partihoning of the ions due to the Galvani potential difference, and it has been shown that the apparent lipophilicity of a number of quaternary ion drugs is not due to ion-pair partitioning as inihally thought [80]. 

The HPLC elution pattern is affected to some extent by the pH of the mobile phase. Moderate pH adjustment to optimize the resolution between EMA and MEMA may be performed. Retention time can be affected greatly by the history of the HPLC column and also the buffer/methanol ratio. The mobile phase ratio should be adjusted to provide adequate separation and retention. Control and fortified samples should be run in the same analytical set with treated samples. 

Investigations on phase ratio are also useful. This does not only affect partition and concentration of components (both water-soluble and poorly water-soluble), but also reduces the reaction inhibition by the product, the substrate excess or any other chemical inhibitor [37,40]. 

COMPARISON OF WCOT AND MICROPACKED COLUMNS HAVING SIMILAR PHASE RATIOS... 

Column Type Length m Internal Diameter mm Film Thickness /tm Phase Ratio Capacity Factor lU mm opi cm/s Column Plate Count Plates Per Meter... 

In gas chromatography the value of the partition coefficient d ends only on the type of stationary phase and the column temperature. It is independent of column type and instrumental parameters. The proportionality factor in equation (l.ll) is called the phase ratio and is equal to the ratio of the volume of the gas (Vg) and liquid (V ) phases in the column. For gas-solid (adsorption) chromatography the phase ratio is given by the volume of the gas phase divided by the surface area of the stationary phase. 

Film Thickness (pa) Capacity Factor Phase Ratio Hass c. Transfer Ten (%) C,... 

---