Optimization of Resolution-Time Ratio with Packed Chromatographic Columns

Loyd, R. J.; Ayers, B. O.; Karasek, F.W.

doi:10.1021/ac60162a040

Cited by 24 publications

(11 citation statements)

References 10 publications

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“…Hence, for late peaks, where the effect of the C term is negligible, a change in outlet pressure or carrier gas lvhich alters the sample diffusivity will change the optimum velocity, but not the minimum value of H. Bohemen and Purnell(1) presented data on the effect on a late peak of a change in gas diffusivity. While they conclude that a high value of diffusivity leads to a high value of R, their data suggest that they did not attain the high ITSlocity required to reach minimum H. The work of Loyd et al (11) on highspeed gas chromatography provides additional confirmation of this observation. For the early peaks, where the contribution of the D term is small, a low value of gas diffusivity can be expected to lower H by reducing the effect of the B term, and, by thus lowering optimum velocity, redure the effect of the C term.…”

Section: Discussionmentioning

confidence: 95%

Gas Chromatography. The Effect of Gaseous Diffusion on Mass Transfer in Packed Columns

Kieselbach¹

1961

Anal. Chem.

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The van Deemter equation relating the H.E.T.P. of a gas chromatographic packed column to carrier-gas velocity predicts that H.E.T.P. will approach a constant for a given column with increasing velocity for samples of very high or very low partition coefficient. In practice, H.E.T.P. goes through a minimum with increasing gas velocity for all samples. Two terms in gas diffusivity, originally proposed by van Deemter and by Jones, are required in addition to the three accepted van Deemter terms to account empirically for the experimental data. This five-term equation is not rigorous, and the data suggest that further study would lead to an equation resembling the form of the Golay equation for H.E.T.P. Experimental data showing the effects of packing particle size and liquid loading are presented. HE THEORY of plate height in gas T chroniatography originally published by van Deemter et al. (IS) relates the height of an equivalent theoretival plate (H.E.T.P.) a t a point along the length of the column to the carrier-gas velocity a t that point. The van Deemter equation expressing this relationship can be written in the following Rimplified form: B H = A + -+ C u U Bohemen and Purnell (1) attempted to fit Equation 1 to their experimental data and obtained unexpected variations in all three ternis with packing particle size, including negative values of .I. Similar results were obtained in unpublished work a t this laboratory. Giddings et al. (3) integrated this and several other equations over the length of the column to correct for the effect of pressure drop on gas velocity, but failcd to obtain a definitive fit to their rxpcrirnental data. Jones (8) presented an equation of the form: (2)where the B term has the same significance as that term in thevan Deemter equation, and E is a coefficient re-B H = ; + E u flecting the effect of gas diffusion on mass transfer.Jones found that liquid diffusivity was not a dominant effect in his experiments and so omitted van Deemter's C term. He and van Deemter later presented consecutive papers (7, 18) a t a meeting in which an attempt was made to reconcile the differences between Equations l and 2 . Van Deemter presented an equation including a gas diffusion term differing from that of Jones, but concluded that this additional term was at least an order of magnitude less significant than his C term.In subsequent discussion, Jones suggested that, in fact, there should be two gas diffusion terms. His E term, added to those presented by van Deemter, produces the equation below in expanded form.where the first four terms are those proposed by van Deemter a t that meeting.The arguments supporting the D and E terms of Equation 3 are as follows:van Deemter's original three-term equation (the first three terms of Equation 3) predicts that H will approach the constant term A as a limit with increasing gas velocity when k is either zero or very large. In practice, H always goes through a minimum with increasing velocity, as shown in the data presented below. In Equation 3, this minimum is...

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Section: Discussionmentioning

confidence: 95%

Gas Chromatography. The Effect of Gaseous Diffusion on Mass Transfer in Packed Columns

Kieselbach¹

1961

Anal. Chem.

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“…A fundamental treatment of separation time in this context is prohibitively difficult and, not surprisingly, most studies of this problem have been limited to separations of binary mixtures (1,(17)(18)(19)(20). The scope and depth of this study imposes a similar restriction.…”

Section: General Considerationsmentioning

confidence: 99%

“…This can be attained from Eq. (17) provided that the PV-relationship for the mobile fluid is known. It would appear that, for most practical operating conditions, the ideal gas law holds sufficiently well.…”

Section: (14)mentioning

confidence: 99%

Basic Equations Relating Separation Time to Relevant Operational Parameters in Chromatography

Smuts

Pretorius

1971

Separation Science

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“…Improved separations at low temperature may replace the more complex gas-liquid or gas-solid columns previously required to give comparable analyses. Low temperature separations may also find advantage for ultrafast analyses in process control (9). Carbon monoxide, methane, ethylene, and other light hydrocarbons, which are prominent in industrial atmospheres, may be easily analyzed.…”

Section: Discussionmentioning

confidence: 99%