Solid phase extraction mixed-mode sorbents

The purification procedure should remove potentially interfering compounds and, moreover, fractionate the entire spectrum of cytokinins into groups. It is usually not possible to analyze nucleotides and O-glucosides together with free bases, ribosides and iV-glucosides. Classical liquid-liquid partition steps [274] have been recently replaced by less labor-intensive, rapid and selective solid-liquid extraction. When applied in neutral aqueous solutions, cytokinin nucleotides are retained on weak anion-exchangers (DEA -Sephadex, DEAE-cellulose), while the other cytokinin forms are retained on reversed phase sorbents. Dobrev and Kaminek [275] used mixed-mode solid-phase extraction for step-wise... 

An understanding of simple methods development is crucial to developing effective environmental applications of solid-phase extraction (SPE). The lour mechanisms outlined in Chapter 2 (reversed phase, normal phase, ion exchange, and mixed mode) are sufficient for the majority of SPE applications in environmental analysis. The molecule s structure and the sample matrix are (he main factors that will determine which mechanism of isolation and separation will be the most appropriate. The fundamental approach to selection of sorbents will be a key topic and many examples are given. This chapter will also discuss applications of SPE to environmental matrices. These include water, soil, and air, for a variety of compounds. 

There have been reports of alkylation of drugs at ion-exchange sites on the surface of some solid-phase extraction columns (Rymut et al., 1996). The authors report that alkyl sulfonates may exist in trace amounts on some of the mixed-mode sorbents, and this can lead to alkylation of basic nitrogen that is primary or secondary (i.e., contains a basic proton that is easily exchangeable). 

Mallet, C.R. et al., Analysis of a basic drug by on-line solid-phase extraction liquid chromatography/tandem mass spectrometry using a mixed mode sorbent, Rapid Commun. Mass Spectrom., 16(8), 805, 2002. 

The extract is collected by depressurization on a column packed with a solid sorbent, in a vessel containing the appropriate solvent, in a collection device connected to a chromatograph, or on combined solid phase-solvent traps [92]. For extraction of volatile compounds, such solvents as acetone, CH2CI2, methanol, or liquid nitrogen are used. Silica gel columns are the most popular way of trapping solids. In this case, the selectivity of the process can be improved by selective elution of the sorbent [88, 92]. SFE can be conducted in a static mode in which sample and solvent are mixed and kept for a user-specified time at a constant pressure and temperature, or in a dynamic mode where the solvent flows through the sample in a continuous manner [56]. The extracted analytes can be collected into an off-line device or transferred to an on-line chromatographic system for direct analysis. 

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