Retention temperature

Cornett RJ (1989) Predicting changes in hypolimnetic oxygen concentrations with phosphorus retention, temperature, and morphometry. Limnol Oceanogr 34 1359-1366... 

By simultaneous optimization of the percent organic modifier in the eluent and the column temperature to keep the retention factors fixed, very efficient, ultrafast separation can be achieved. The researchers conclude that for fast separations, the relationship between retention, temperature, and volume fraction of organic modifier needs to be taken into account. As the temperature increases, a lower volume of organic modifier is needed to speed up HPLC. Therefore, a highly retentive column... 

Tr = column temperature at emergence of peak (retention temperature),... 

According to this equation, the retention temperature for any particular solute and column should depend only upon the ratio r/F. The retention temperature (TR) may be calculated from the isothermal retention volume by graphical integration of the above equation. 

In order to achieve the same degree of separation in an isothermal analysis as in a programmed temperature run, a temperature 45 °C below the retention temperature of a pair of peaks should be selected. 

Expressed as a formula, if Tris the retention temperature, i.e. the temperature of the oven at the time of elution, and T0 the recommended isothermal temperature, then... 

Rf passes through the quartz column at a lower retention temperature compared to Hf. This observation received considerable attention and was interpreted as evidence for relativistic effects, since the higher volatility of RfCl4 compared to that of HfCl4 is unexpected on the basis of classical extrapolations. 

Contaminants may arise from impure starting materials, incomplete reactions and secondary reaction products. A knowledge of these factors serves to limit the list of probable contaminants to a small number. Tentative identifications of some of the contaminants shown as minor peaks in the chromatograms were assigned by matching their retention times (or retention temperatures) with those of probable contaminants. In the case of the six carboxylic acids of Table II, the contaminants are known to be carboxylic acids, since the method of purification involves repeated precipitations as the ammonium salts. The tridecanedioc acid observed in the octadecanedioc acid (compound 10 of Table IV) is considered the source of the lower homolog impurity to-(p-chlorophenyl)-octadecyl bromide (compound 6 of Table IV). 

To speak of the retention volume is usually inappropriate in temperature programming instead, the characteristic quantity is retention temperature Tr, the temperature reached by the column at the solute peak maximum. Retention temperature is related to heating rate, mobile-phase flow rate, and isothermal retention volumes. In temperature programming, as indicated above, the rate of band movement increases sharply with time. Nevertheless, even with isothermal elution, solute bands do not move at a uniform rate, but more rapidly as the carrier gas expands from the inlet to the outlet of the column. For a band at a distance z from the column inlet, the rate of movement is given by... 

FIGURE 24-10 Characteristic curves of rfF against retention temperature for the hydrocarbons ranging from propane (1) to octane (6) obtained from the chromatographic system of Figure 24-4. Solid lines, calculated from isothermal data points, experimental. From Harris and Habgood. )... 

This equation indicates that the retention temperature may be related to the program in a characteristic way as defined by rjF. Note that the ratio of heating rate to flow rate is the significant variable, rather than either one alone, and that retention temperatures can be obtained from the isothermal retention volumes over the temperature range Tq to Tj. ... 

Because of the relative high column temperature that had to be used (Dexsil 300 275-350°C by temperature programming OV-1 330°C isothermal) bleeding took place and also deterioration of the column. This resulted in poor separation and the formation of artefacts after some days or weeks of use of the column. A chromatogram of some permethylated glycoalkaloids is found in Figure 19.1 and the relative retention and the retention temperatures in Table 19.1. 

RELATIVE RETENTION AND RETENTION TEMPERATURES OF PERMETHYLATED GLYCOALKALOIDS1... 

Alkaloid (permethylated) Relative retention Retention temperature,°C... 

Duplex retention temperature at which 50% of oligomer hybrids remain intact (during wash)... 

The rate of uplift of the Transantarctic Mountains has been measured by the fission-track method which is briefly reviewed in Appendix 15.7.1 and was described in detail by Faure and Mensing (2005). The fission-track method is well snited for this purpose because uranium-bearing ntinerals (e.g., apatite) retain fission tracks only after the ntinerals have cooled to the track-retention temperature which for apatite is 60°C (Gleadow and Fitzgerald 1987). 

The temperature is an important variable because uranium-bearing minerals anneal fission tracks at elevated temperatures and retain them quantitatively only after the temperature has decreased below the level at which all tracks are preserved. Therefore, the fission track date of a mineral or glass is the time that has elapsed since the specimen cooled through the track-retention temperature for the last time. In other words, fission track dates are equal to the age of a specimen of mineral or glass only in cases when the specimen cooled to the track-retention temperature immediately after it was formed. The fission-track method appears to be straightforward in principle but is, in fact, quite labor intensive and demanding (Faure and Mensing 2005). 

At any non-isothermal conditions of GC analysis, all analytes can be characterized not only by retention times ( r), but also by the so-called retention temperatures, Tr, especially those that are directly proportional to the retention times at linear temperature programming (r = const), Tr= To + rt, where Tq is the initial temperature. Hence, relationships (7) and (8) can be rewritten by including Tr values instead of r, for example ... 

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