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Other Optimization Techniques and Retention Parameters

In essence, the brute-force method starts with an intentionally too strong mobile phase. .. ttiis is key. This ensures that all analytes will elute in a reasonably short time. In fact, under these conditions, many or all analytes may co-elute. The first mobile phase composition tested may be 90/10 acetonitrile/water. The next step is to sequentially weaken the mobile phase until an acceptable separation is achieved. For example, the next mobile phase may be 80/20 acetonitrile/water. Assessment of the optimal conditions (including separation, elution time, and peak shapes) dictates the subsequent tests. For example, severe tailing indicates that a buffer system (e.g., acetate) or mobile phase modifier (e.g., THF) be added in the next iteration. This flexibility is not an inherent aspect of the triangulation optimization method. The aspect of experience comes into pl with the choice and level of buffers and mobile phase modifiers. Sequential modifications to the mobile phase ate made until the optimal separation is achieved. [Pg.61]

Other parameters have been used to help predict solute retention with varying mobile phases. Solubility parameters, 6 [69,70], octanol/water partition coefficients. [Pg.61]

FIGURE 2.10 Window diagram for the separation of 2-phenyIpropionic add (PPA), phenylsucdnic acid (PSA), 4-hydroxybenzoic acid (40H), and benzoic acid (BA). The highest point under the composite curve offers the best resolution. This occurs at a pH 4.1 with an a value of approximately 1.5. [Pg.62]


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