Optimization touching bands

Investigators dealing with optimization of chromatography systems for preparative separation on laboratory or larger scales in the first stage using TLC selected stationary and mobile phases to obtain a resolution Rj > 1.5 for each pair of touching bands. Such a resolution permits the introduction of a 3 mg/g adsorbent. 

Direct scale-up of an analytical HPLC method at touching-band conditions is feasible only when there is a need for small (mg) amounts of the isolated material and the mobile phase does not contain nonvolatile additives. Using a touching-band optimization technique, the amount of material loaded may be increased until visible peak broadening occurs and the first sign of overlapping between the product peak and closely retained impurities is observed. The amount of product that may be loaded onto a column under touching-band conditions can be estimated as [5]... 

Optimizing load until elution profiles start to overlap (touching bands)... 

Minimization of the total elution and cycle time results in higher productivity and lower eluent consumption. Optimizing the selectivity can be contradictory to these parameters. However, if the cycle time is minimized the productivity for touching band operation increases. 

Optimization for Touching Bands Using the Ideal Model.871... 

Knox and Pyper [17] made the first systematic study of the optimization of the experimental conditions in preparative liquid chromatography based on the use of a simple chromatographic model. They considered touching band separation (i.e., in the ideal model, tR 2 — 1e (Figure 8.6), or approximately a imit resolution between the two bands) with the following assumptions ... 

Golshan-Shirazi and Guiochon have investigated the optimization of the experimental conditions using the analytical solution of the ideal model [20-24]. In the case of touching bands, the recovery yield is practically total ( 100%). Therefore, the same experimental conditions assure the maximum production rate for both components. Their assumptions are limited to the following two ... 

Using this model, several optimization problems have been discussed—the touching band problem (this section) and the overlapping band problems, with or without a recovery yield constraint (next two sections). 

After the column has been packed and equilibrated with the mobile phase, the flow rate is optimized by injecting small samples and increasing the flow rate until the resolution obtained is approximately equal to 1.7-2 if the separation must be carried out under touching-band condition, or a resolution near unity if the separation is done under overlapping band condition. 

Efficiency of the packing material is an important consideration in the PHPLC optimization process. When the load is kept sufficiently small, not exceeding the value corresponding to the touching band, it is obvious that the higher efficiency allows injection of more feed. Scale-up of better than baseline analytical separation often benefits from increased production rate of the target material. However,... 

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