Automation of Solid-Phase Extraction

Automation of solid-phase extraction (SPE) is an important contribution to sample processing. If many samples are to be analyzed in the laboratory, automation provides precise and accurate methods when compared to manual methods. This chapter will discuss three major ideas on automation. First is why automate SPE. Second are the types of automation hardware, and third, how to automate an SPE method is discussed. Finally several case studies will be examined that show the automation process taken from a manual method. 

Automation of solid-phase extraction protocols has been successfully implemented using continuous flow injection based systems. 

Automation of solid-phase extraction for riboflavin separation has been carried out in both offline and online modes, in the last case with direct coupling to the injection valve of HPLC equipment. 

Analysis of pesticides in water was performed by fully automated online solid-phase extraction-liquid chromatography-tandem mass spectrometry (SPE-LC-MS/ MS) [25, 31]. These pesticides (a total of 22 belonging to the classes of triazines, OP, chloroacetanilides, phenylureas, thiocarbamates, acid herbicides, and anilides) were selected on the basis of previously published studies [20, 25], information gathered from the water authorities, and known use in rice crops. 

Bourgogne E., Grivet C., and Hopfgartner G., 2005. Determination of talinolol in human plasma using automated online solid phase extraction combined with atmospheric pressure chemical ionization tandem mass spectrometry. J Chromatogr B 820 103. 

Lacorte S. and Barceld D., 1995. Determination of organophosphorus pesticides and their transformation products in river waters by automated online solid-phase extraction followed by thermospray liquid chromatography. J Chromatogr A 712 103. 

Rodriguez-Mozaz S., de Alda M.J.L., and Barcelo D., 2004. Picogram per liter level determination of estrogens in natural waters and waterworks by a fully automated online solid-phase extraction-liquid chromatog-raphy-electrospray tandem mass spectrometry method. Anal Chem 76 6998. 

Other techniques to improve throughput are instrumentation based and may involve multiple HPLC systems. The simplest method involves the automated use of solid phase extraction cartridges for sample cleanup followed by direct injection into the mass spectrometer [114], Coupling of multiple HPLC systems to one mass spectrometer allows one column to equilibrate and separate while another column to flow into the mass spectrometer. Multiple HPLC systems may be configured such that the mass spectrometer is only exposed to each serial HPLC eluent as the analyte of interest is eluted [115,116]. Although multiple H P LC-based methods may increase throughput, they also typically decrease sensitivity and may confound data workup and interpretation. 

Angelo HR, Petersen A. 2001. Therapeutic drug monitoring of haloperidol, perphenazine, and zuclopenthixol in serum by a fully automated sequential solid phase extraction... 

Solid-phase extraction columns offer a rough cleanup of the crude extract, which might nevertheless not be sufficient for some detection systems such as mass spectrometry. Some authors have proposed a combination of solid-phase extraction and liquid chromatography columns for extract cleanup (440). Other methods appeal to liquid chromatography on Cig columns with automated fraction collection. Fractions containing the analyte of interest were evaporated to dryness, yielding a residue that in most cases was suitable for gas chromatographic detection after suitable derivatization (445, 437). 

Koal, T., Sibum, M., Koster, E., Resch, K., and Kaever, V. (2006). Direct and fast determination of antiretroviral drugs by automated online solid-phase extraction-liquid chromatography-tandem mass spectrometry in human plasma. Clin. Chem. Lab. Med. 44 299-305. 

While analytical derivatizations are an effective way for extracting compounds, these often require additional steps in the analytical procedure and can introduce side products that may interfere with the analysis. Solid phase extraction has provided an alternative method to this process. The advantage of solid phase extraction is that the reagents, derivatives, and side products are maintained on the solid phase. As needed, these derivatives and side products can be selectively eluted after the desired derivative has been formed on the column. In addition, this method can eliminate potential problems associated with emulsion formulation that may occur with liquid-liquid extraction of compounds from the biological matrix. Finally, solid phase extraction is easily amenable to automation with other analytical detection methods such as gas and liquid chromatography. The phases used in solid phase extraction are the standard ones employed in other extraction methods. ... 

In a limited version, only the most critical stages are automated by the use of robots with limited, strictly defined movements examples are automated processes of solid-phase extraction (SPE), heating, and mixing. The robots are controlled by a computer and the operator chooses the suitable values of the parameters from given ranges (e.g., autosampler). 

Raisglid, M., Burke, M. E, and Van Horne, K. C. 1993. Factors affecting the reliability of solid-phase extraction for environmental analysis. International Symposium on Laboratory Automation and Robotics, Amsterdam, pp. 1-7. 

The use of solid-phase extraction (SPE) for the sample preparation of drugs and pharmaceuticals has increased over the last 15 years because of ease of operation, increased selectivity with many new phases, and interfacing of automation and robotics. A simple strategy now exists for SPE methods development of drugs and pharmaceuticals, which makes sample preparation extremely straightforward. This strategy is the use of generic mixed-mode SPE and is discussed in detail in this chapter. 

The second type of automation is the workstation. They are instruments that can perform multiple functions using software tools and dedicated hardware to perform a set of predefined operations, which are related to or part of the process of solid-phase extraction. They differ from laboratory robots that are capable of many laboratory functions. There are seven instruments that will be discussed in this section (Table 10.2-10.8), which are dedicated to solid-phase extraction. They range in price from approximately 20,000 to 50,000 (1996 dollars) for workstations and from 50,000 and up for laboratory robots. 

Jensen, B.H. Larsen, C. Quantitation of diltiazem in human plasma by HPLC using an end-capped reversed-phase column. Acta Pharm.Nord., 1991, 3, 179—180 Leneveu, A. Stheneur, A. Bousquet, A. Roux, A. Automated high-performance liquid chromatographic technique for determining diltiazem and its three main metabolites in serum. J.Liq.Chromatogr., 1991, 14, 3519-3530 [serum extracted metabolites SPE pharmacokinetics LOD 2.5 ng/mL] Bonnefous, J.L. Boulieu, R. Comparison of solid-phase extraction and liquid-liquid extraction methods for liquid chromatographic determination of diltiazem and its metabolites in plasma. 

Aguilar, C., Ferrer, I., Borrull, F., Marce, R. M., and Barcel6, D., Comparison of automated online solid-phase extraction followed by liquid chromatography-mass spectrometry with atmospheric pressure chemical ionization and particle beam mass spectrometry for the determination of a priority group of pesticides in environmental water, J. Chromatogr. A, 794, 147-163, 1998. 

P. Hinsmann, L. Arce, A. Rios and M. Valcarcel, Determination of pesticides in water by automation online solid-phase extraction-capillary electrophoresis, J. Chromatogr. A, 866, 137-146, 2000. 

The major sample preparation techniques that are amenable to automation are solid-phase extraction, LC, dialysis, microwave sample preparation, flow injection analysis, and segmented flow analysis. Other sample preparation techniques, such as liquid-liquid extraction or ultrafiltration, may be possible to automate but may not be cost effective. This shortlist of amenable techniques may constrain an analysis, but there is a large body of experience in the literature to help a novice to use these procedures. 

Kema, I.P. Meijer, W.G. Meiborg, G. Ooms, B. Willemse, P.H. de Vries, E.G. Profiling of tryptophan-related plasma indoles in patients with carcinoid tumors by automated, online, solid-phase extraction and HPLC with fluorescence detection. Clin. Chem. 2001, 47, 1811-1820. 

Supercritical fluids have an advantage of solid-phase extraction compared to liquids due to the lower and adjustable density. For analytical purposes, liquid extraction methods are often simpler and more easily automated than the supercritical fluid extraction (SFE). 

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