A New Approach to Linear Temperature Programming Calculations

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Gas Chromatography Theory in qualitative analysisRetention index in isothermal and temperature programmed analysis (part 1) Simple dead volume calculations with three known compounds Summary A definition for an absolute retention index is given. This index is independent of whether the process is isothermal or temperature programmed. The relation between this index and Kovats's index is discussed. General equations are derived for the retention times of homologous series, from which the position of the air peak or missing members can be determined.Methods used in the literature for air peak determination are improved and extended toother cases of interest. The retention index in temperature programmed chromatography is reexamined in the light of recent publications on temperature programming.

Section: For Member N + R One Getsmentioning

confidence: 78%

Section: The Retention Index In Temperature Programmed Chromatographymentioning

confidence: 83%

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The absolute retention index in chromatography. Part 1

Said

Hussein

1978

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Proof of the constancy of Δ T_f during homologous series temperature programming

Said

Al-Saadoon

1981

Figure lgives the distribution of the componentsofa homologous series along the column. Figures 1 a, 1 b, and 1 c give the distribution when components n, n + 1, and n + 2 are i3t the column outlet, respectively. If the relative volatility cl was not a function of temperature, then Figures 1 a, 1 b, and 1 c would be identical except that each component r would be replaced by component r+ 1 in thefollowingfigure.Since clisafunction oftemperatureand usually decreases as the temperature increases, and also since the difference in temperature between consecutive figures is small (about 15OC), then the distances will be very slightly displaced (by about 2 to 3%) as we go from one figure to the next.We let x1 be the fraction covered by component n + 1 at temperature Tn when n is at the column outlet and x p be the fraction covered by component n + 2 when n + 1 is at the outlet. 10251In Table 1, the vapor pressure values listed were taken from ref.[3]and the a values were calculated from the vapor pressure ratios.The If the fractional decrease in CL corresponding to ATf is equal to 6, then the corresponding fractional increase in x is equal to G(a-l)/a where(a-l)/a isameasureofthe column fraction covered bycomponent n + 1 between T, and Tn + 1. For homologous series, a is usually in the neighborhood of 2. This leads to or 2) T,+ -T,+ = T,+, -T, = ATf = constant.Assumption 2 is what we are really trying to establish. It can be used however to calculate the value of the correction factor f which will turn out to be close to 1. This, in turn, justifies the use of assumption 2.With these assumptions, eq. InFurthermore, for the purpose of calculating the change of a with temperature, the relative volatility a between two neighboring members of a homologous series, like the paraffin series, may be taken equal to the ratio of the vapor pressures of the pure components at the same temperature.To calculate f for the following casesIll. Tn = 450 K, ATf = 2OoC Table 1 Vapor pressure and relative volatility of paraffin hydrocarborns. V. P. [Ibs/in2]Relative volatility Temp.[OF]

Flow of the carrier gas in open‐tubular capillary columns in temperature‐programmed gas chromatography

Hevesi

Krupčík

1997

Key Words:Capillary gas chromatography Temperature programmed gas chromatography Modelling of separation Carrier gas flow Summary A second-order non-linear partial differential equation was derived to describe the dependence of carrier gas pressure in the column on the column distance and the time under temperature programmed conditions. This equation was solved numerically by the modified finite difference method for various column parameters. Constant inlet and outlet pressures were used as boundary conditions. The retention times calculated with the derived procedure were compared to those calculated on assumption of a constant pressure profile along the column. Significant differences between retention times of corresponding solutes calculated by the two methods were found, especially when relatively long columns (L > 50 m) with small internal diameter (d c 0.3 mm) and high temperature program rates (r > S"/min) are used.