SPE cartridge

Recently, SPE cartridges and disks have been widely and successfully used in preconcentration processes [1-3]. They reduce solvent usage, disposal costs, and extraction time for sample preparation and obtain large enrichment factors. 

The concentration mode is used when the extract from the SEE module is not concentrated enough to be directly analyzed by the CE instrument, and thus requires a concentration step, which is carried out in the concentrator device. In this mode, during the concentration step the extract from the SEE cell enters the first valve (positioned in the concentration mode (Eigure 6.11(a)), and is then directed to and adsorbed into the sample concentrator which contains an SPE cartridge. While the... 

Figure 11.16 Chromatograms of plasma samples obtained by using SPE-SFC with super-aitical desorption of the SPE cartridge (a) blank plasma (20 p.1), UV detection at 215 nm (b) blank plasma (20 p.1), UV detection at 360 nm (c) plasma (1 ml) containing 20 ng mitomycin C (MMC), UV detection at 360 nm. Reprinted from Journal of Chromatography, 454, W. M. A. Niessen et al., Phase-system switching as an on-line sample pretreatment in the bioanalysis of mitomycin C using supercritical fluid cliromatography, pp. 243-251, copyright 1988, with permission from Elsevier Science.

Figure 13.11 shows the chromatogram obtained for a surface water sample spiked with various chorophenoxy acids at a level of 0.5 p.g 1 under the same conditions as previously and after enrichment on a Cjg column and clean-up on silica SPE cartridges. 

Whilst for the analysis of plant material for cannabinoids both GC and HPLC are commonly used, in analytical procedures the employment of GC-based methods prevails for human forensic samples. Nonetheless, the usage of HPLC becomes more and more of interest in this field especially in combination with MS [115-120]. Besides the usage of deuterated samples as internal standards Fisher et al. [121] describe the use of a dibrominated THC-COOH (see 7.5). The usage of Thermospray-MS and electrochemical detection provide good performance and can replace the still-used conventional UV detector. Another advantage in the employment of HPLC rather than GC could be the integration of SPE cartridges, which are needed for sample preparation in the HPLC-system. 

Another equally important consideration before development of a determinative or confirmatory method is an understanding of the chemical properties of the analyte. Such an understanding becomes the cornerstone of a successful method since the unique chemical properties of each analyte provide the basis for isolation and detection schemes. Table 1 lists some of the important chemical properties that could be considered. For example, knowing the or p/fb of an analyte could influence the choice of a liquid-liquid extraction scheme, solid-phase extraction (SPE) cartridge, mobile phase pH, or mass spectrometric ionization. Knowing the overall polarity of the analyte can be very helpful in the evaluation of an extraction or separation. Currently, computational methods are available to obtain an estimate of the logP... 

When selecting the most appropriate SPE cartridge to use, several factors may influence the decision. One consideration is the chemical properties of the marker residue such as polarity and Polar analytes will be retained to a greater ex-... 

A technique that attempts to combine the extraction and SPE into a single step is matrix solid-phase dispersion (MSPD). In this technique, a nonpolar (such as Cig) SPE sorbent is blended directly into tissue matrix, the mixture is packaged into an SPE cartridge, and the cartridge is eluted like a typical SPE cartridge. The advantage of MSPD is reduced sample size and increased efficiency due to a reduced number of steps. 

Oily crops such as soybeans and canola (oilseed rape) cannot be extracted with aqueous buffers, because the extraction solvent cannot permeate the hydrophobic plant tissue matrix. In these cases, homogenization in acetonitrile-hexane is recommended. This solvent mixture is able to extract sulfonylureas from these samples with a minimum of co-extracted oil. After extraction, the sulfonylureas partition into the acetonitrile phase while most of the oil stays in the hexane phase. Further cleanup is accomplished using a silica SPE cartridge and normal-phase conditions. 

Water samples of 500-1000 mL are extracted and purified simultaneously through an SPE cartridge such as Carbograph-1, Cig and RP-18, usually followed either by HPLC with ultraviolet (UV) or photoconductivity detection or by GC/ECD. The acidic-type diphenyl ether herbicides are derivatized with diazomethane and various kinds of chloroformates and determined by GC and HPLC. 

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