Solid phase extraction process

Chapuis F et al (2004) Retention mechanism of analytes in the solid-phase extraction process using molecularly imprinted polymers - application to the extraction of triazines from complex matrices. J Chromatogr B Anal Technol Biomed Life Sci 804(1) 93-101... 

N. Masque, M. Galia, R. M. Marce and F. Borrull, Chemically modified polymeric resin used as sorbent in a solid-phase extraction process to determine phenolic compounds in water , J. Chromatogr. 771 55-61 (1997). 

Figure 6 The solid-phase extraction process, including column conditioning, sample loading, optional washing, and analyte elution.

Figure 12-1. A summary of the solid phase extraction process. (Courtesy - Supelco, Inc., Bellefonte, PA)...

Valcarcel and co-workers proposed in 2003 an automatic system for the determination of riboflavin in lyophilized food products using a solid-phase extraction process that included columns filled with cotton or silica C18 for the sequential retention of synthetic colorants and natural colorants, respectively (Gonzalez et al. 2003). In this case riboflavin was assessed as an authorized natural colorant for total estimation of this class of compounds. The analytical characteristics of this methodology are summarized in Table 18.3. 

Prepai ative isolation of nonvolatile and semivolatile organic compounds fractions (hydrophobic weak acids, hydrophobic weak bases, hydrophobic neutrals, humic and fulvic acids) from natural and drinking waters in optimal conditions was systematically investigated by solid-phase extraction method with porous polymer sorbents followed by isolation from general concentrate of antropogenic and/or toxic semivolatile compounds produced in chlorination and ozonation processes. 

Braga et al. ° compared the efficiencies of several processes, i.e., hydrodistillation, low pressnre solvent extraction, and Soxhlet and supercritical fluid extraction. For each process, the inflnences of several parameters (duration, temperature, nature of solvent) were also evalnated. These authors concluded that the Soxhlet method performed with ethanol/isopropanol 1/100 v/v for 2 hr and 30 min was the most effective. Snn et al. nsed solid phase extraction to concentrate (nine times) a... 

SAMPLE PROCESSING PROBLEMS IN SOLID-PHASE EXTRACTION... 

Solid phase extraction (SPE) involves the separation of components of samples in solution through their selective interaction with and retention by a solid, particulate sorbent. SPE depends on differences in the affinities of the various components of the sample for the sorbent. The mechanisms of the interactions are virtually identical to the sorption processes that form the basis of liquid chromatographic separations (p. 80). The choice of solvent, the pH and ionic strength of aqueous solutions, and the chemical nature of the sorbent surface, especially its polarity, are all of importance in controlling the selectivity and efficiency of an extraction. 

The most common (off-line) sample preparation procedures after protein precipitation are solid phase extraction and liquid-liquid extraction. Multiple vendors and available chemistries utilize 96-well plates for solid phase extraction systems and liquid-liquid extraction procedures. Both extraction process can prepare samples for HPLC/MS/MS assay. Jemal et al.110 compared liquid-liquid extraction in a 96-well plate to semi-automated solid phase extraction in a 96-well plate for a carboxylic acid containing analyte in a human plasma matrix and reported that both clean-up procedures worked well. Yang et al.111 112 described two validated methods for compounds in plasma using semi-automated 96-well plate solid phase extraction procedures. Zimmer et al.113 compared solid phase extraction and liquid-liquid extraction to a turbulent flow chromatography clean-up for two test compounds in plasma all three clean-up approaches led to HPLC/MS/MS assays that met GLP requirements. 

Due to the predicted and previously detected low concentrations of pesticides in environmental samples (usually around the nanogram per liter level), a preconcentration step of the water samples is necessary prior to measurement. In this way, a preconcentration factor of several orders of magnitude (200-1,000-fold) is mandatory to reach the low detection limits necessary for the identification of pesticides, especially in complex wastewater samples. Also, the use of surrogate standards (e.g., triphenyl phosphate) added before the extraction step is a common practice in order to account for possible errors during the extraction process and for quantitative purposes. The commonly used extraction methods for polar compounds from water matrices involve isolation using liquid-liquid extraction (LLE) and solid-phase extraction (SPE), which are commented on below. Other methods such as semipermeable membrane devices (SPMD) are also mentioned. 

In the case of batch processing the scavenger is added to the reaction mixture after completion. For flow-through processing the scavenger is packed into a column (solid-phase extraction, HPLC, etc.) and the reaction mixture is passed through the column until scavenging is complete. 

The Gilson Aspec automatic sample preparation system is a fully automated system for solid-phase extraction on disposable columns and online HPLC analysis. The Aspec system offers total automation and total control of the entire sample preparation process including clean-up and concentration. In addition, Aspec can automatically inject prepared samples into on-line HPLC systems. 

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. 

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