Binary eluent

Another important parameter is the eluent composition. Binary mixtures (and obviously pure solvents) should be preferred to complex mixtures, since new systems perform an on-line analysis of the composition of binary eluents. These eluent systems allow the automatic eluent recycling, with a reduced number of controls. 

Use of 10 pm LiChrosorb RP18 column and binary eluent of methanol and aqueous 0.1 M phosphate buffer (pH 4.0) according to suitable gradient elution program in less than 20-min run time with satisfactory precision sensitivity of spectrophotometric detection optimized, achieving for all additives considered detection limits ranging from 0.1 to 3.0 mg/1, below maximum permitted levels Simultaneous separation (20 min) of 14 synthetic colors using uncoated fused silica capillary column operated at 25 kV and elution with 18% acetonitrile and 82% 0.05 M sodium deoxycholate in borate-phosphate buffer (pH 7.8), recovery of all colors better than 82%... 

The following Soezewinski equation is a simple linear relationship with respect to logA, linking the retention parameter (i.e., R,J) of a given solute with quantitative eomposition of the binary eluent applied ... 

Assuming that the adsorbent surface is occupied by an adsorbed solute molecule (Ag) and a molecule of a stronger solvent (n ) which are equal to one another, the elution strength of a binary eluent, shows the following dependence on its quantitative composition ... 

Coupling Equation 2.16 and Equation 2.17, we can obtain the following relationship, which describes the dependence of the solute s retention parameter, R, on the quantitative composition of a given binary eluent ... 

By contrast, it is often not possible to standardize cleanup steps based on adsorption chromatography. Altered volumes of elution solvent, small deviations in the water content of the adsorbent and minor changes in the composition of binary eluents are often necessary and should be regarded as minor changes. 

Vab = the corrected elution volume of the solute (experimental elution volume-void volume) in the binary eluent A+B, with volume fractions B, respectively. 

In the case of a binary eluent system the dependence of the capacity factor on the volume fraction of the component with the higher elution strength (C) can be calculated by... 

Fig. 5. Transition from the exclusion to the adsorption separation mode through critical conditions for polystyrene standards at a varying composition of the binary eluent (CCI4—CHC13). (Column Si-300, flow rate u = 0.5 rnl/min, volume of.santple 10 pi, UV detector, >, = 275 nm, t = 27 °C)...

Fig. 18a-c. Transition through the critical conditions for hydroxyl-containing polyibutylene tereph-thalate) at a varying composition of heptane-tetrahydrofuran binary eluent. (Column Si-60, u = 1 mi/ min, volume of the sample 10 pi, UV detector, X = 254 nm, t = 24 °C)... 

In binary eluents, k depends on the composition of the mobile phase. This dependence is approximately given through ... 

Binary eluent. A two-solvent blend used as the mobile phase. 

It is essential that while setting the conditions for the differential mass-balance equation we did not define the function of the excess adsorption isotherm. We can now use the expression (2-46) for measurement of the model independent excess adsorption values. It is convenient to use it for the study of the adsorption behavior of binary eluents [22]. 

Equation (2-46) is only applicable for binary systems (analyte—single component mobile phase). Similar expression could be derived if we assume that the adsorption of the analyte does not disturb the equilibrium of the binary eluent system. 

Equation (2-46) is applicable for the description of adsorption behavior of binary eluent in the column. In the isocratic mode, the column is equilibrated at given composition of the eluent. Any small volume of the mixture of eluent... 

Effect of the eluent composition could be discussed on the basis of equation (2-55). In the simple case of binary eluent (organic/water mixture), we can consider in the first approximation that Gibbs free energy of the eluent interaction with the packing material surface is a linear function of the eluent composition... 

The binary eluent adsorption equilibrium is considered to be not disturbed by the injection of a small amount of the analyte (essentially the third component in the system). In an isocratic mode at a fixed eluent composition, the organic adsorbed layer is a stationary phase for the analyte to partition into. The analyte can partition into the adsorbed layer followed by consequent adsorption on the surface of the reversed-phase adsorbent. The overall retention is a superposition of two consecutive processes. Since the eluent component adsorption could be measured independently and adsorbed layer volume could be represented as a function of the mobile phase composition, the analyte retention also could be expressed as a function of the eluent composition. 

Applying this function into the mass-balance equation (2-33) and performing the same conversions [Eqs. (2-34)-(2-39)], the final equation for the analyte retention in binary eluent is obtained. In expression (2-67) the analyte distribution coefficient (Kp) is dependent on the eluent composition. The volume of the acetonitrile adsorbed phase is dependent on the acetonitrile adsorption isotherm, which could be measured separately. The actual volume of the acetonitrile adsorbed layer at any concentration of acetonitrile in the mobile phase could be calculated from equation (2-52) by multiplication of the total adsorbed amount of acetonitrile on its molar volume. Thus, the volume of the adsorbed acetonitrile phase (Vj) can be expressed as a function of the acetonitrile concentration in the mobile phase (V, (Cei)). Substituting these in equation (2-67) and using it as an analyte distribution function for the solution of mass balance equation, we obtain... 

A chromatographic system consisting of the binary eluent (e.g., acetonitrile-water) with liophilic salt added in low concentration (not more than lOOmM), along with basic analyte, is considered here. Adsorption behavior of acetonitrile in the column has been discussed in Section 2.12, and we assume that low concentrations of liophilic salt additives and injection of small amount of the analyte does not noticeably disturb its adsorption equilibrium. 

Each constant in the equation above represents single equilibrium process, which is assumed to be independent on other equilibria in the column. Equation (2-93) describes the retention of basic ionizable analytes in reversed-phase chromatographic system with binary eluents and liophilic counteranions added. Similar expression could be derived for the behavior of anionic analytes in the presence of liophilic countercation. 

In a binary eluent system (acetonitrile-water), an adsorbed organic phase with finite thickness and composition different from the bulk mobile phase is preferentially accumulated near the surface of the bonded phase. The organic layer accumulated near the bonded ligands could behave as a liquid stationary phase in reversed-phase HPLC, and it contributes to the overall analyte retention process. 

The reliable range of is less than one and a half decades. When dealing with a series of analytes of diverse retentive properties it is hence necessary to determine Rm values at several compositions of binary eluents and next to extrapolate linearly the relationship between R and the volume percent of one of the eluent components to a fixed value. In the case of reversed-phase TLC extrapolation is usually performed to pure water (buffer) as a hypothetical eluent. Such an extrapolated Rm value is usually denoted by... 

HPLC retention data for QSRR analysis are usually obtained by measuring log at several eluent compositions (isocratic conditions) and then extrapolating the dependence of log on a binary eluent composition to a fixed mobile phase composition, common for all the analytes studied, based on the Soczewinski-Snyder model ... 

In this chapter we discuss limiting conditions of solubility. These conditions were observed for polymers of varying polarity (PS and PMMA) using binary eluent mixtures that combined a polar nonsolvent with either a polar or nonpolar solvent. 

RP-HPLC with a reversed -phase packed columns is normally used for polar compounds. By varying the per cento of binary eluent system (Me0H-H20) it is possible to separate substances ranging from to terpenic and flavonoidic glycosides. 

The formation of N-methylsuccinimide (NMS), succinimide and 2-pyrrolidone (2P) (Table 1) was expected by Campbell and Striebig (1999) and Friesen et al. (1999) who performed OH-oxidation of NMP in alkaline solutions and by photocatalysis, respectively. We performed the HPLC analysis using the same C18 column as described above, and a UV detection at 202 nm. A binary eluent (80 %/20 % acetonitrile/water) was used at 1 mL min. ... 

From Eq. 5.1 we can obtain the p/if at the inflection point from the plot of retention factor vs pH in the particular binary eluent system. 

It is possible to obtain a desired elution strength by mixing two solvents. A choice of binary mixtures is shown in Fig. 9.4. If, for example, a solvent strength of 8 = 0.4 is needed, this can be obtained by the following binary eluents ... 

VS. log X plots obtained for alumina in binary eluents, it is visible that in the case of the covering of a heterocyclic nitrogen by a methyl group or by a condensed ring, flat adsorption of the molecule is possible. 

In Fig. 4 the dependence between e of pure component of binary eluent and volume ratio of the second component is shown. The data are dissipated around the line, although Baran et al. [67] has found perfect linear dependence using the same column packing (3 points plotted in Fig. 4). Again, difference in adsorptive properties of silica gels (and/or measurements at different temperatures) maybe reason for dissipation of points. Such linear dependence can be useful at forecasting of... 

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