Solvent strength optimization

Solvent Strength Optimization, at http //www.biotage. com/Print.aspx id=21978 (accessed August 2007) Talamona, A. Laboratory Chromatography Guide Buchi Labortechnik AG Flawil, Switzerland, 2007 12-26. 

When multiple development is performed on the same monolayer stationary phase, the development distance and the total solvent strength and selectivity values (16) of the mobile phase (17) can easily be changed at any stage of the development sequence to optimize the separation. These techniques are typically fully off-line modes, because the plates must be dried between consecutive development steps only after this can the next development, with the same or different development distances and/or mobile phases, be started. This method involves the following stages ... 

On the basis of Snyder s system for characterization of solvents the PRISMA method for mobile phase optimization has been developed. This system enables the optimization of solvent strength and mobile phase selectivity and also the transfer of the optimized mobile phase to different planar chromatographic techniques, in our case the PLC. 

In 1996, Snyder and Dolan elaborated the linear solvent strength (LSS) approach allowing the evaluation of log few from a single gradient run and its precise determination from two gradient runs [48]. From a practical point of view, LSS is the most useful approach to describe theoretical aspects and LSS gradients are convenient for optimization studies. Several commercially available optimization software packages which are able to predict resolution or retention in RPLC are currently based on this approach. 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

SELECTION OF OPTIMAL LINEAR SOLVENT STRENGTH GRADIENTS IN LIQUID CHROHATOGRAPHy... 

Solvent optimization in reversed-phase liquid chromatography is commenced by selecting a binary mobile phase of the correct solvent strength to elute the seuaple with an acceptable range of capacity. factor values (1 < k <10 in general or 1 < k < 20 when a larger separation capacity is required). Transfer rules (section 4.6.1) are then used to calculate the composition of other isoeluotropic binary solvents with complementary selectivity. In practice, methanol, acetonitrile and tetrahydrofuran are chosen as the selectivity adjusting solvents blended in different... 

The optimization of the solvent strength by varying the selectivity points has to be carried out until at least a beginning separation is obtained. At this point the third part of the PRISMA iK>del can be used to select the appropriate development mode. If an Increase in efficiency is required to improve the overall resolution of the sample then forced-flow linear... 

Glajch, J. L., Kirkland, J. J., Squire, K. M., and Minor, J. M., Optimization of solvent strength and selectivity for reversed-phase liquid chromatography using an interactive mixture-design statistical technique, /. Chromatogr., 199, 57, 1980. 

Snyder L.R., Dolan J.W., Molnar I., and Djordjevic, N.M., Selectivity control in reversed-phase HPLC methods development varying temperature and solvent strength to optimize separations, LC-GC, 15 (2), 136, 1997. 

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