Monolith solid-phase extraction

Peterson DS, Rohr T, Svec FK, Frechet JMJ (2003) Dual-function microanalyt-ical device by in situ photolithographic grafting of porous polymer monolith integrating solid-phase extraction and enzymatic digestion for peptide mass mapping. Anal Chem 75 5328... 

Asperger A. et al., 2002. Trace determination of priority pesticide in water by means of high-speed online solid-phase extraction-liquid chromatography-tandem mass spectrometry using turbulent-flow chromatography columns for enrichment and a short monolithic column for fast liquid chromatographic separation. J Chromatogr A 960 109. 

Zang X. et al., 2005. A novel online solid-phase extraction approach integrated with a monolithic column and tandem mass spectrometry for direct plasma analysis of multiple drugs and metabolites. Rapid Commun Mass Spectrom 19 3259. 

Still, a lot needs to be done to develop large monolithic units, which would handle kilogram and larger production scales and guarantee to the process managers the stability of the support and its presence on the market over several decades. However it is realistic to expect that SMC will attract widespread use within a decade in a variety of applications, from chromatography to bioconversions, solid phase extractions and solid phase synthesis. 

Although the history of rigid monolithic polymers is relatively short, a number of applications have already been explored. These applications cover a rather broad range of fields from heterogeneous catalysis and solid-phase extraction, to polymer-supported chemistry and a variety of separation processes. 

Section II covers the latest trends in reducing sample preparation time, including direct sample infusion/injection and on-line solid phase extraction (SPE). In Section III, we focus on newer trends in stationary phases and how these phases hope to offer different selectivities compared to current CIS-based phases. Section IV briefly provides a few observations on how new detectors are increasing the versatility of HPLC. Finally, in Section V we examine monolithic columns, small particles packed in short columns, high-temperature LC, ultra high-pressure LC, and parallel injection techniques. 

Yu, C., Davey, M. H., Svec, F, and Frechet, J. M. (2001). Monolithic porous polymer for on-chip solid-phase extraction and preconcentration prepared by photoinitiated in situ polymerization within a microfluidic device. Anal. Chem. 73, 5088-5096. 

Tan, A., Benetton, S., and Henion, J. D. (2003). Chip-based solid-phase extraction pretreatment for direct electrospray mass spectrometry analysis using an array of monolithic columns in a polymeric substrate. Anal. Chem. 75, 5504—5511. 

By far the most studied PolyHIPE system is the styrene/divinylbenzene (DVB) material. This was the main subject of Barby and Haq s patent to Unilever in 1982 [128], HIPEs of an aqueous phase in a mixture of styrene, DVB and nonionic surfactant were prepared. Both water-soluble (e.g. potassium persulphate) and oil-soluble (2,2 -azo-bis-isobutyronitrile, AIBN) initiators were employed, and polymerisation was carried out by heating the emulsion in a sealed plastic container, typically for 24 hours at 50°C. This yielded a solid, crosslinked, monolithic polymer material, with the aqueous dispersed phase retained inside the porous microstructure. On exhaustive extraction of the material in a Soxhlet with a lower alcohol, followed by drying in vacuo, a low-density polystyrene foam was produced, with a permanent, macroporous, open-cellular structure of very high porosity (Fig. 11). 

S. Lubbad, S.A. Steiner, J.S. Fritz, and M.R. Buchmeiser, Metathesis polymerization-derived monolithic membranes for solid-phase extraction coupled with diffuse reflectance spectroscopy, J. Chromatogr. A, 1109(1) 86—91, March 2006. 

Up to now, most efforts have been directed towards the preparation of uniformly sized spherical MIP particles in the micrometre range. This is the obvious consequence of the need for this kind of materials as fillers for high-performance chromatographic columns, capillaries for electrophoresis, cartridges for solid-phase extractions and other applications requiring selective stationary phases. Additionally though, strategies for the preparation of other more sophisticated MIP forms, such as membranes, (nano)monoliths, films, micro- and nanostructured surfaces etc. 

The first monolithic materials initially emerged in the 1960s, but it is during the last 20 years that monoliths have been intensively developed in a variety of fields and particularly in analytical chemistry for separation techniques. Nowadays, these macroporous materials are widely used and have found numerous applications in different chromatographic modes such as liquid chromatography (LC) or CEC, as indicated by several reviews [150, 151]. Less commonly, monolithic materials can also be applied, for example, to solid-phase extraction, combinatorial synthesis and for enzyme immobilisation. 

Recently, a method for preparing MIP monolithic columns for electrophoresis, chromatography and solid-phase extraction has been developed, which uses a preformed polymeric monolith, onto which an MIP with specific recognition sites is subsequently grafted [149, 179-181]. 

Although potentially useful for sample preparation by solid-phase extraction, monolithic MIP phases had initially only been applied as stationary phase for LC... 

The fabrication of imprinted monolithic solid-phase microextraction fibres has been developed for the selective extraction and preconcentration of diacetylmorphine and its structural analogues, triazines, bisphenol A, anaesthetics, and antibiotics followed by GC or HPLC analysis [156,163,179,196,197]. In addition, the on-line coupling of the imprinted monolith as a preconcentration column with a conventional analytical column has been proposed for the enrichment and cleanup of environmental and food samples [163]. However, at present, the capacity of the imprinted fibres and thus the degree of recovery of analytes are very variable and obviously need some improvement. For example, the recoveries of triazines after SPME with an imprinted monolith prepared by in situ polymerisation of MAA as... 

Other than beads, porous polymer monoliths, which were photopolymerized in a COC chip, were used for solid-phase extraction. It is known that priming polymeric surfaces is not as simple as priming silica surfaces, which use a common surface primer agent, TMPM. Therefore, the grafting method as initiated by UV should be used to attach the polymer monoliths [588]. A similar strategy was used for sample pre-concentration of PAHs (e.g., pyrene). Pyrene (900 nM) was first concentrated by 400-fold in 24% ACN before switching to 56% ACN for CEC separation (see Figure 5.5) [148]. 

A monolithic hydrophobic polymer formed by photoinitiated polymerization for on-chip solid-phase extraction is shown in Figure 5.6. The polymer mixture includes butyl methacrylate (BMA) and ethylene dimethacrylate (EDMA), with the pore size controlled by the composition of the hexane/methanol porogenic mixture. The degree of pre-concentration depends on the flow rate, as shown in the pre-concentration of GFP at three flow rates (see Figure 5.7). The factors of pre-concentration were 355, 756, and 1002 for the flow rates of 3, 1.03, and 0.53 rE/min, respectively [342]. 

Peterson, D.S. Rohr, T. Svec, F. Frechet, J.M.J. Dual-function Microanalyti-cal Device by In Situ Photolithographic Grafting of Porous Polymer Monolith Integrating Solid-Phase Extraction and Enzymatic Digestion for Peptide Mass Mapping, Anal. Chem. 75, 5328-5335 (2003). 

Aboul-Enein, H.Y., Ali, I., and Hoenen, H., Rapid determination of haloperidol and its metabolites in human plasma by HPLC using monolithic silica column and solid-phase extraction, Biomed. Chromatogr., 20(8), 760, 2006. 

H.M. Oliveira, M.A. Segundo, J.L.F.C. Lima, V. Cerda, Multisyringe flow injection system for solid-phase extraction coupled to liquid chromatography using monolithic column for screening of phenolic pollutants, Talanta 77 (2009) 1466. 

A small, 20 X 1 mm ID, monolithic rod, obtained by the polymerization of 80% tec/i-DVB in a mixture of dodecanol and toluene, was employed for the solid-phase extraction of polar organic compounds from aqueous solutions [415]. It was demonstrated again that by maintaining constant dilution of the monomer and changing only the weight percent ratio of toluene to dodecanol from 2 58 to 10 50, it is possible to increase the surface area of the sorbent from 188 to 348m /g and to reduce the mean pore diameter... 

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