Reversed-phase HPLC isotherms

Batchwise guest-binding experiments are also used to evaluate the imprinting efficiency. The polymer particles of suitable size (usually <32 pm) are put into sample tubes, and atrazine solutions of known concentrations (typically in CHCl3) are added. The resulting suspensions are stirred for a predetermined period of time. After this incubation, the polymer particles are filtered off, and the concentrations of atrazine in the solution are determined by reversed-phase HPLC. When the concentration of atrazine after the incubation is subtracted from the initial concentration, the quantity of atrazine bound by the polymer is determined. By doing similar experiments at various concentrations of atrazine, the binding isotherms are obtained and the data are analyzed by the Scatchard method. 

Polynuclear Aromatic Hydrocarbons (Method 610). The polynuclear aromatic hydrocarbons (PAHs) are analyzed by HPLC by using a reverse-phase HC-ODS Sil-X column with UV and fluorescence detectors in series. The option to use FID-GC is given. The column is 1.8-ft X 2-mm i.d. containing Chromosorb W-AW-DCMS coated with 3% OV-17. It is operated isothermally at 100 °C for 4 min and then programmed at 8 °C/min to 280 °C. 

A unified theory recently proposed to explain the manner of sorption and the form of sorption isotherm in gas, liquid, and ion-exchange chromatography is presented in some detail. Selectivity in reversed-phase high-pressure liquid chromatography is explored at length. Several chapters deal with characterization of bonded phases, relationship of column-packing structure and performance, variability of reversed-phase packing materials, and the differences between silica-based reversed-phase and poly(styrene-divinylbenzene) columns. A short review is included to cover various approaches used in HPLC to achieve the desired selectivity for resolution of enantiomeric compounds. 

However, Kazakevich and co-workers demonstrated the importance of the adsorption of chaotropic ions onto the reversed stationary phase [106]. The rank of an ion in the Hofmeister series is another measure of its tendency to accumulate at the stationary phase in RP-HPLC and be quantified via its adsorption isotherm [88]. Clearly a specific surface excess of the chaotropic reagent results in the development of a potential difference between the stationary phase and the bulk eluent, modulating retention of analytes [107]. We discussed in Chapter 3 the way a comprehensive theory can take this experimental evidence into account. 

---