HPLC methods packing materials

LC techniques are widely diffused for the determination of hydrophilic but not volatile and thermally unstable pesticides. Since the European Community Directive [68] indicates 0.1 pg L" as the concentration threshold level for a single pesticide in waters destined for human consumption, to quantify these concentration levels, suitable pre-concentration and extraction procedures must be generally performed prior to the HPLC determination. The extraction methods are based on LLE, MAE, on-line continuous flow liquid membrane extraction (CFLME), and mainly on SPE and SPME. Many SPE procedures are used the packing materials are graphitized carbon, ODS, styrene-divinylbenzene co-polymers, or selective phases based on immunoafflnity. The extraction can be performed on- and off-line, manually, or in a semi-automated way. 

The particle size distribution of packing materials has been shown to vary not only from one manufacturer to another but also with the measurement method used. For HPLC specifications, it is normal for manufacturers to give a particle size distribution based on an area distribution. However, this distribution has been pointed out [30] not to give a true distribution of the fine material... 

We now have a fairly adequate understanding of the different properties, including the particle diameter i/p, the pore size, the degree of permeability, and the chemical composition of the surface of the support matrix, to know which type of stationary phase can be successfully used with a particular class of peptides. Most of the HPLC packing materials now in use for peptide separations are based on the wide pore microparticulate silica gels with polar or nonpolar carbonaceous phases chemically bonded to the surface of the matrix. Methods for the preparation of these chemically bonded stationary phases, their available sources of supply. 

---