Amino NPLC column

Surfactants are separated according to adsorption or partitioning differences with a polar stationary phase in NPLC. This retention of the polar surfactant moiety allows for the separation of the ethylene oxide distribution. Of all the NPLC packings that have been utilized to separate nonionic surfactants, the aminopropyl-bonded stationary phases have been shown to give the best resolution (Jandera et al., 1990). The separation of the octylphenol ethoxylate oligomers on an amino silica column is shown in Fig. 18.4. Similar to the capabilities of CE for ionic surfactants, the ethylene oxide distribution can be quantitatively determined by NPLC if identity and response factors for each oligomer are known. 

In NPLC, which refers to the use of adsorption, i.e. liquid-solid chromatography (LSC), the surface of microparticulate silica (or other adsorbent) constitutes the most commonly used polar stationary phase normal bonded-phase chromatography (N-BPC) is typified by nitrile- or amino-bonded stationary phases. Silica columns with a broad range of properties are commercially available (with standard particle sizes of 3, 5 and 10 im, and pore sizes of about 6-15nm). A typical HPLC column is packed with a stationary phase of a pore size of 10 nm and contains a surface area of between 100 and 150m2 mL-1 of mobile phase volume. 

Monomeric HALS have been determined by HPLC [470,663]. Excellent separation was achieved for HALS-type samples (Tinuvin 770 and Chimassorb 944) with NPLC-PDA (230 nm) using an amino column with acetonitrile/water as the mobile phase RPLC using C or cyano columns was not effective [664]. 

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