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The correct measurement and interpretation of evaluation factors in chromatography: The real plate number, the separation number, the dosage quality. Part 1: Gas chromatography

Summary

The correct evaluation of separation columns, capillary columns, their interconnections and the dosage technique is important in gas chromatography as well as in liquid chromatographic methods.

The conventional, theoretical plate number or plate height and their corresponding effective values (effective plate number or effective plate height) respresent the combined action of column quality, interconnections and dosage, rather than their individual contributions to the overall performance of the separation system. Since these chromatographic criteria are dependent on the nature of the sample and the methods, a directed improvement or selective evaluation is not possible. A new evaluation system and method of measurement with the following characteristics is proposed:

  1. 1.

    Substance independent, i. e., independent of the chromatographic position.

  2. 2.

    Real evaluation of a separation column.

  3. 3.

    Individual, quantitative evaluation and measurement of factors which have a negative influence on the overall performance of a separation system, such as dosage, interconnections and detector.

  4. 4.

    A meaningful correlation between the basic factors, which determine the separation capability and the separation power. The real plate number nreal the real plate height hreal the dosage and interconnection quality Os the separation number TZreal the separation power number TZt

and the independent optimization of these factors, with respect to a maximum separation allow a correct, comparative evaluation of entirely different chromatographic separation systems. Such an evaluation requires three to eight data pairs, consisting of (correctly measured) peak width and retention data and a statistical regression calculation or inter- and extrapolating by plotting. The measurements and calculations can be carried out within 5 minutes. Highly conclusive evaluation factors (which must be statistically secured by additional calculations) are obtained. The basic evaluation procedures will be explained, and examples will be given for the method of measurement, the calculation and plotting techniques. (programs for the Hewiett-Packard calculator HP-67 or 97 is provided.) Applications will be discussed for conventionally packed columns, extremely short or long micropacked columns, and thin film capillaries. Part 2 deals with adaptation of the method to liquid column chromatography, and part 3 discusses the application of the method to high performance and normal layer chromatography as well as a comparison of the methods.

It is often claimed, that the theoretical plate number is “theoretically” dependent on k and that the air peak (in GC) cannot be used to evaluate the quality of a chromatogram. This is an interpretation error or a mis-understanding of the method of measurement and will be discussed in depth, thus the basis of the new method can be critically compared and examined with the conventional evaluation method. The derivations are designed in such a way, that newcomers in the field, will be able to apply the method.

The theoretical background of this paper is discussed in Chromatographia 1976 and 1977.

References

  1. [1]

    R. E. Kaiser, Gas-Chromatographie (1959) Monographie, Verlag Geest und Portig, Leipzig 1960. (b0 in der Trennstufenzahl)

  2. [2]

    Many private conversations since 1959, speaches by J. F. K. Huber, Vienna.

  3. [3]

    Grob, K., Grob, G., Chromatographia5, 3 (1972) (direct sample injection).

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Kaiser, R.E. The correct measurement and interpretation of evaluation factors in chromatography: The real plate number, the separation number, the dosage quality. Part 1: Gas chromatography. Chromatographia 10, 323–338 (1977). https://doi.org/10.1007/BF02263008

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