Liquid Adsorption Chromatography LAC

These NELC techniques can be classified into five types. Each type requires gradient elution with two or more solvents. The first type is liquid adsorption chromatography (LAC) (Table I). In LAC, initial and final mobile phases should be good solvents for the sample copolymers. Silica gel is used as the stationary phase in most cases. The sample co-... 

The first step in the characterization of polymers is to fractionate the unknown sample, and then to determine the stmctures of the separated fractions. Separation is best performed by modem liquid chromatographic methods. Depending on the kind of heterogeneity it is necessary to select the most suitable chromatographic method, i.e. either Size-Exclusion Chromatography (SEC) or Liquid Adsorption Chromatography (LAC). Furthermore, the meanwhile well-established Liquid Adsorption Chromatography at Critical Conditions (LACCC) is also used. A separation system that operates near critical conditions sometimes has to be applied. 

A combination of liquid adsorption chromatography (LAC)-SEC, or SEC-LAC, has recently been developed by several workers. Danielewicz and Kubin [66] separated random copolymers of P(S-MMA) and styrene-ethyl methacrylate according to chemical composition on a silica gel column, with a mixture of 1, 2-dichloroethane (DCE) and THE as the mobile phase. Separation was almost independent of the sample molecular mass. 

Each type of interaction chromatography requires a mobile phase that comprises two or more solvents. In liquid adsorption chromatography (LAC), the initial and final mobile phases are good solvents for the polymer. In most cases, silica gel is used as the stationary phase. The sample injected into the column adsorbs on the silica surface at the initial mobile phase. For very-low-molar-mass samples, the adsorption might be sufficiently weak and desorption in the same mobile-phase composition may take place. In this case, elution takes place under isoaatic conditions. 

LAC(CC) Liquid adsorption chromatography LPGC Low-pressure gas chromatography... 

Much more important than GC are the different techniques of LG. Using SEC, LAC or liquid chromatography at the critical point of adsorption (LCCC) polymers can be fractionated with respect to different aspects of molecular heterogeneity, including molar mass, funcdonality, and chemical composition. As will be shown in the next applications, LC can be efficiently... 

---