Retention time mobile phase

Flow of Mobile Phase Retention Time in Plate Volumes... 

MeOH in mobile phase Retention time R (min) Capacity factor k Log k ... 

Pyka separated 16 PAHs (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo [a] anthracene, chrysene, benzo[/>]fluoranthene, benzo[fe]fluoranthene, benzo[a]py-rene, dibenzo[a,/z]anthracene, benzo[g,/i,i]perylene, and indeno[l,2,3-C(i]pyrene) according to the Environmental Protection Agency (EPA) by gradient HPLC on a LiChrospher PAH column using acetonitrile and water as mobile phases. Retention times fr (sec) of investigated PAHs were correlated with topological indices based on the adjacency matrix (M, 012) and the... 

Retention factor A measure of the amount of time an analyte spends in the stationary phase relative to the mobile phase Retention time The time taken for an analyte to travel from the point of injection to the point of detection within an HPLC system Reverse phase chromatography Describes the chromatographic separation in which the stationary phase is nonpolar and the mobile phase is composed of an aqueous, moderately polar liquid Robustness A measure of a method s ability to withstand small but deliberate changes in the method parameters it provides an indication of its reliability during normal usage Selectivity factor See separation factor... 

Hexamethylpropyleneamine oxime (HMPAO) stereoisomers and their technetium-99m complexes were resolved on a 40°C Chiralcel OD column [614]. The d- and /-uncomplexed isomers were separated in 20 min using a 97/3 hexane/IPA (0.01% diethylamine) mobile phase. The ""Tc complexes were also resolved but with an 85/15 hexane/IPA mobile phase. Temperature increases from 20°C to 40°C greatly improved peak shape and resolution. A table of resolution for the Tc complexes of meso-, d- and /-HMPAO was generated for 90/10 to 0/100 hexane/IPA mobile phases. Retention times for 65/35 to 85/15 hexane/IPA were also tabulated. For all these mobile phases the retention times were under 15 min. 

The basis of chromatography is in the differential migration of chemicals injected into a column. The carrier fluid takes the solutes through the bed used for elution (mobile phase). The bed is the stationary phase. Based on mobility, the retention-time detectors identify the fast and slow-moving molecules. Based on internal or external standards with defined concentration, all unknown molecules are calculated in a developed method by software. GC columns are installed in an oven which operates at a specified temperature. A diagram of an oven with GC column is shown in Figure 7.16. 

During their passage through the column, sample molecules spend part of the time in the mobile phase and part in the stationary phase. All molecules spend the same amount of time in the mobile phase. This time is called the column dead tine or holdup time (t.) and is equivalent to the tine required for an unretained solute to reach the detector frsolute retention time (t,) is the time between the instant of saiq>le introduction and when the detector senses the maximum of the retained peak. This value is greater than the column holdup time by the amount of time the solute spends in the stationary phase and is called the adjusted retention time (t, ). These values lead to the fundamental relationship, equation (1.1), describing retention in gas and liquid chromatography. 

Kd = the solute s organic solvent water distribution coefficient. k = chromatographic capacity ratio (k — tr — t0/t0, tr and t0 being solute retention time and mobile phase holdup time, respectively), a and b = coefficients whose magnitudes depend on the LL distribution and RPLC systems. 

This chapter focuses on gas-liquid chromatography, in which compounds in a sample are separated based on vapor pressures and differences in affinity for the stationary phase (a high boiling point liquid) versus the gaseous mobile phase. The time between sample injection and detection of the individual compound eluting from the column is called the retention time. Compounds that have limited solubility in the stationary phase will exit the column quickly as a large proportion will remain in the mobile phase. Compounds with polarity similar to that of the stationary phase will have longer retention times and potentially broader peaks, due to increased interaction with the stationary phase. 

A.26.14 (a) The partition coefficient ratio is the ratio of die time the analyte spends in the mobile phase compared stationary phase. Tlreoretical plates refers to the number of times an analyte partitions between the phases. Retention time is the time required for die analyte to travel past the stationary phase, (b) Answers will vary. 

Mobile phase holdup time it is also equal to the retention time of an unretained compound referred to as air peak ... 

Retention Behavior. On a chromatogram the distance on the time axis from the point of sample injection to the peak of an eluted component is called the uncorrected retention time The corresponding retention volume is the product of retention time and flow rate, expressed as volume of mobile phase per unit time ... 

A chromatographic peak may be characterized in many ways, two of which are shown in Figure 12.7. The retention time, is the elapsed time from the introduction of the solute to the peak maximum. The retention time also can be measured indirectly as the volume of mobile phase eluting between the solute s introduction and the appearance of the solute s peak maximum. This is known as the retention volume, Vr. Dividing the retention volume by the mobile phase s flow rate, u, gives the retention time. 

A solute s capacity factor can be determined from a chromatogram by measuring the column s void time, f, and the solute s retention time, (see Figure 12.7). The mobile phase s average linear velocity, m, is equal to the length of the column, L, divided by the time required to elute a nonretained solute. 

Use of column selectivity to improve chromatographic resolution showing (a) the variation in retention time with mobile phase pH, and (b) the resulting change in alpha with mobile phase pH. 

In liquid-solid adsorption chromatography (LSC) the column packing also serves as the stationary phase. In Tswett s original work the stationary phase was finely divided CaCOa, but modern columns employ porous 3-10-)J,m particles of silica or alumina. Since the stationary phase is polar, the mobile phase is usually a nonpolar or moderately polar solvent. Typical mobile phases include hexane, isooctane, and methylene chloride. The usual order of elution, from shorter to longer retention times, is... 

Thus far all the separations we have considered involve a mobile phase and a stationary phase. Separation of a complex mixture of analytes occurs because each analyte has a different ability to partition between the two phases. An analyte whose distribution ratio favors the stationary phase is retained on the column for a longer time, thereby eluting with a longer retention time. Although the methods described in the preceding sections involve different types of stationary and mobile phases, all are forms of chromatography. 

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