Zone spreading, analysis

In a follow-up study, the same authors examined the applicability of the same device for relevant protein samples and investigated the main contributions to band broadening [82]. As a consequence of the small depth of the beds, zone spreading caused by Joule heating was shown to be negligible (see Sect. 3.1.1). Cross fields of up to 100 V/cm were applied for the separation of human serum albumin, ribonuclease A and bradykinin. The feasibility of fraction collection was demonstrated with four collected fractions of a whole rat plasma sample. Off-line analysis of these four isolated fractions by CE indicated the separation of serum albumins and globulins. 

A simplified general analysis of zone spreading in chromatography leads to the following expression (Giddings 1961). 

In 1977 Krishnamurthy and Subramanian published an exact theoretical analysis of FFF [19], based on their generalized dispersion theory. Without touching on the details of a complicated mathematical treatment, with the aid of which they solved the problems of both the separation and dispersion processes that occur in the FFF channel during the complete separation from the injection to the elution, let us only say in general that their solution makes it possible to explain some experimental artefacts in detail. These artefacts could not be explained by means of the non-equilibrium theory of FFF mentioned above, which is based on some asymptotic assumptions. Perhaps the most important discrepancy between the theory and the experimental data is that the zone spreading that is observed is considerably larger than the spreading predicted by the theory. 

Except TFFF, all of the other subtechniques of FFF involved the establishment of a parabolic velocity profile. If the profile is not parabolic and is asymmetric with regard to the longitudinal central axis of the channel, and can be described by a general function of a polynomial type, both theoretical retention and zone spreading will correspond to this distribution of velocities across the channel. Theoretical analysis of this general problem was performed by Martin and Giddings [70]. 

The Qixiashan lead-zinc deposit is a hydrothermal lead-zinc mineralisation in a cataclastic fault zone in limestone. The ore body is 300 m below surface, and the overburden comprises 30 m of Quaternary alluvium. Soil samples were collected along a traverse over the mineralisation in three successive years and analysed for CO2 (Fig. 4-4). The samples from Year 1 yielded the highest CO2 concentrations and broadest anomaly, but contrast is poor. In Year 2 the anomaly is about 200 ppm CO2 and is best developed around a fault that cuts the mineralisation at depth. Anomaly contrast is put at 4.2. Samples were taken from a depth of 80 cm in Year 3, compared to 30 cm in earlier years the resulting CO2 pattern, however, is closely similar to that found in Year 2. Analysis of bore hole samples for CO2, Hg, Pb, Zn, Cu and Ag showed that the Qixiashan deposit is vertically and horizontally zoned (Fig. 4-5). The highest CO2 concentrations are found close to the richest ore. The CO2 halo extends upward on the hangingwall side of the deposit and spreads laterally. This halo is much better developed above the mineralisation than those of the base and precious metals only the Hg halo extends as far upward, and it is also rather wider. 

Axial dispersion (sometimes referred to as backmixing) is a spreading of the concentration profile in the axial direction due to flow variations within the adsorbent bed (see the pulse analysis section in Appendix C). This effect can also contribute to the spreading of the mass transfer zone. 

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