Equipment solid-phase extraction

Method and equipment solid phase extraction and high performance liquid chromatography (HPLC)/diode array detection. 

Figure 2.12 Schematic representation of an on-line SPE-GC system consisting of three switching valves (VI-V3), two pumps (a solvent-delivery unit (SDU) pump and a syringe pump) and a GC system equipped with a solvent-vapour exit (SVE), an MS instrument detector, a retention gap, a retaining precolumn and an analytical column. Reprinted from Journal of Chromatography, AIIS, A. J. H. Eouter et al, Analysis of microcontaminants in aqueous samples hy fully automated on-line solid-phase extraction-gas chromatography-mass selective detection , pp. 67-83, copyright 1996, with permission from Elsevier Science.

Insufficient testing is one of the major causes of method failure. The amount of data needed to publish a new procedure in a peer-reviewed journal and the procedural detail supplied therein are often insufficient to allow a different user to validate a method rapidly. The developer should evaluate if the method will work using chemicals, reagents, solid-phase extraction columns, analytical columns, and equipment from various vendors. Separate lots of specific supplies within a vendor should be evaluated to determine if lot-to-lot variation significantly impacts method performance. Sufficient numbers of samples should be assayed to estimate the lifetime of the analytical column and to determine the effects of long-term use on the equipment. 

Solid-phase extraction (SPE) cartridge, LC Si 2-g, 12-mL (Supelco), or equivalent ABC Laboratories Model SP 1000 gel permeation chromatograph system equipped with a 2.5 x 32.0 cm glass column of Bio-Beads S-X3 Select 200-400 mesh (ca 50 g, Bio-Rad Laboratories) preconditioned with ethyl acetate-cyclohexane (1 1, v/v), or equivalent... 

Milbemectin consists of two active ingredients, M.A3 and M.A4. Milbemectin is extracted from plant materials and soils with methanol-water (7 3, v/v). After centrifugation, the extracts obtained are diluted to volume with the extraction solvent in a volumetric flask. Aliquots of the extracts are transferred on to a previously conditioned Cl8 solid-phase extraction (SPE) column. Milbemectin is eluted with methanol after washing the column with aqueous methanol. The eluate is evaporated to dryness and the residual milbemectin is converted to fluorescent anhydride derivatives after treatment with trifluoroacetic anhydride in 0.5 M triethylamine in benzene solution. The anhydride derivatives of M.A3 and M.A4 possess fluorescent sensitivity. The derivatized samples are dissolved in methanol and injected into a high-performance liquid chromatography (HPLC) system equipped with a fluorescence detector for quantitative determination. 

Equipment and Instrumentation. Solid-phase extraction columns were obtained from J. T. Baker. Octadecyl (C18) and octyl (C8) 1-mL low-displacement columns were used as the primary extraction columns. Cyano and diol... 

Additional reagents and equipment for fractionating crude polyphenolics by solid-phase extraction into anthocyanin and nonanthocyanin fractions unit 11.2)... 

G Scarano, M Esposito, L Grasso, V Soprano, G Oliviero. Use of automated solid-phase extraction equipment for the determination of ivermectin residues in animal liver by HPLC. Analyst 123 2541 -2553, 1998. 

The most simple and common workstations are those for dilution and/or reagent addition to a number of samples in a simultaneous manner, either to all samples in a rack or to a line with a slide z-axis (as in the Biomex" 2000 model from Beckman). Most workstations are designed to operate with liquid samples such is the case with those from Cyberlab, Gilson, Zymark, SciLog, Sagian, Beckman and Hamilton, which manufacture specific equipment for liquid handling, solid-phase extraction and preparation of liquid... 

At the time of this writing, there are at least six main suppliers of solid-phase extraction equipment and supplies. At least three of the suppliers offer technical guides and general solid-phase extraction literature.1-4 Table 1 lists the companies and their Internet sites. Thurman and Mills provide a comprehensive list of SPE product suppliers in their book Solid Phase Extraction (Wiley, 1998).5... 

TABLE I Solid-Phase Extraction Equipment and Suppliers... 

Examples of this approach has been reported by Janiszewski [10] and others [53] by utilizing extraction disks in a 96-well format to perform quick, automated solid-phase extractions under very simple wash and elution conditions. In one approach [10], a Tomtec Quadra 96-well workstation was used to perform the semiautomated solid-phase extraction with Empore C extraction disks. The advantage of this piece of equipment is that it allows liquid to be transferred to or from all 96-wells simultaneously, thus giving the greatest throughput advantage. 

The sample introduction system must be capable of introducing a known and variable volume of sample solution reproducibly into the pressurized mobile phase as a sharp plug without adversely affecting the efficiency of the column. The superiority of valve injection has been adequately demonstrated for this purpose and is now universally used in virtually all modern instruments for both manual and automated sample introduction systems [1,2,7,31,32]. Earlier approaches using septum-equipped injectors have passed into disuse for a several reasons, such as limited pressure capability, poor resealability, contamination of the mobile phase, disruption of the column packing, etc., but mainly because they were awkward and inconvenient to use compared with valves. For dilute sample solutions volume overload restricts the maximum sample volume that can be introduced onto the column without a dramatic loss of performance. On-column or precolumn sample focusing mechanisms can be exploited as a trace enrichment technique to enhance sample detectability. Solid-phase extraction and in-column solid-phase microextraction provide a convenient mechanism for isolation, concentration and matrix simplification that are easily interfaced to a liquid chromatograph for fully or semi-automated analysis of complex samples (section 5.3.2). 

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