Solid-phase extraction, with sample pretreatment

The second method uses preconcentration to increase the analyte concentration in the absorption solution to detectable levels prior to analysis. One example is the use of solid-phase extraction with an anion exchange column as a pretreatment technique to remove interference from the sample matrix and to enhance the detection sensitivity prior to determination of the concentrated iodide anion through reversed phase high-performance liquid chromatography (HPLC) using an ultraviolet (UV) detector. The results show more than 90% recovery and good reproducibility for the determination of trace iodine in iodine-enriched eggs. 

Pankey et al.21 described a rapid, reliable, and specific enzyme multiplied immunoassay technique (EMIT ) for amitriptyline, nortriptyline, imipramine, and desipramine in sera. To overcome crossreactivity, solid phase extraction was included in sample pretreatment. Disposable 1 mL columns packed with covalently labeled silica gel were conditioned with HPLC-grade methanol (1 mL) and then with de-ionized or distilled water (1 mL). Serum (calibrator, control, or patient sample, 500 L) was applied onto the column, eluted to waste, washed with 900 /uL of wash solution containing acetonitrile (236.1 g/L) and ion-pairing reagent in acetate buffer, pH 4.2, washed with 500 fiL of mobile phase solution containing acetonitrile (393.5 g/L) in methanolic phosphate buffer, pH 7.0,... 

The sample pretreatment steps for surfactant analysis such as extraction and concentration can be carried out in a variety of ways. Most of the common and well tested procedures have been described by Schmitt [46]. Solid phase extraction (SPE) with C2, Cg or Cis and divinyl benzene resins as well as special phases, e.g. graphitised carbon black (GCB), can be adequate methods, especially for SPE of metabolites from... 

For analyzing amphenicol residues in liquid samples such as milk, a pretreatment centrifugation step for fat removal is usually required (21, 22). Dilution of milk samples with water prior to solid-phase extraction cleanup is also often needed (23, 24). Semisolid samples such as muscle, kidney and liver, require, however, more intensive sample pretreatment. The most popular approach for tissue break-up is through use of a mincing and/or a homogenizing apparatus. 

Prior to analysis of -lactam residues in liquid foods such as milk, a pretreatment step for fat removal, accomplished by centrifugation (69-71), is usually required. In instances where milk is to be submitted to ultrafiltration, dilution with water/acetonitrile (72-76) or water/acetonitrile/methanol (77-79) is often needed. Milk filtration (80) or dilution with acetate (81, 82) or phosphate buffers (83) is sometimes essential prior to solid-phase extraction. Unlike milk, semisolid food samples such as muscle, kidney, and liver require normally more intensive sample pretreatment. Tissue break-up is mostly carried out by the combined use of a mincing apparatus and a tissue homogenizer. 

When analyzing milk samples for nitro furan residues, dilution with sodium chloride solution (155) or lyophilization (156) prior to extraction may be required. Dilution of egg samples with water prior to their solid-phase extraction has been also reported (157). Semisolid samples such as muscle, kidney, and liver, require a more intensive sample pretreatment. This involves use of a mincing apparatus followed by sample homogenization in water (37), sodium chloride solution (155), or dilute hydrochloric acid (158). 

When liquid samples such as serum, plasma, milk, or honey are not to be extracted using direct liquid-liquid partitions with organic solvents but through use of solid-phase extraction or matrix solid-phase dispersion techniques, dilution with water (323, 324), phosphate buffer saline (325), or phosphoric acid (326, 327) is often the only sample preparation procedure applied. Milk analysis sometimes requires further pretreatment for fat removal (328). Centrifugation at about 7000g at 4-10 C for 20 min is the usually applied procedure for making the fat floating on top of milk readily eliminated. 

Fig. 19 Randomly scattered low internal standard (IS) responses observed for incurred samples only, whose IS responses were within normal range during repeat analyses. Analyte olanzapine IS olanzapine-d3 sample pretreatment at clinic 25 % (w/v) L-ascorbic add added to plasma in a ratio of 1.25 100 (v/v) extraction MCX (mixed-mode strong cation exchange)-based solid-phase extraction. An incurred sample was coded for reassay when its IS response was outside 50 % of the mean IS response of the accepted calibration standards and quality controls. Reproduced from ref. [36] with permission from Elsevier...

Ahrer et al. [69] developed methods for the determination of drug residues in water based on the combination of liquid chromatography (LC) or capillary electrophoresis (CE) with mass spectrometry (MS). A 2 mM ammonium acetate at pH 5.5 and a methanol gradient was used for the HPLC-MS allowing the separation of a number of drugs such as paracetamol, clofibric acid, penicillin V, naproxen, bezafibrate, carba-mazepin, diclofenac, ibuprofen, and mefenamic acid. Apart from the analytical separation technique, water samples have to be pretreated in order to get rid of the matrix components and to enrich the analytes the usual way to accomplish this aim is to perform a solid-phase extraction... 

Figure 11.3 Separation of potato tissue glycoalkaloids on an amino phase [reproduced with permission from K. Kobayashi, A.D. Powell, M. Toyoda and Y. Saito, J. Chromatogr, 331 (1989)]. Conditions sample, extract from young potato plantlets after solid-phase extraction pretreatment column, 30cm x 3.9mm i.d. stationary phase, [xBondapak NH2 mobile phase, ethanol-acetonitrile-potassium dihydrogenphosphate (3 2 1) UV detector, 205 nm. Peaks 1 = a-chaconine with Rq =/3-D-glucose, R2 — R3 —a-i-rhamnose 2 — a-solanine with Rl =/3-D-galactose, R2 = /3-D-glucose, R3 —a-L-rhamnose.

Fig. 13-9. Gas chromatogram of die interlaboratory test of Sample B. Alkaline sample pretreatment with solid phase extraction.

As illustrated by the examples given in Table 3, the application of labs-on-chips to real samples is still limited. This is partly due to the fact that the analytical assay is only the final step of the whole procedure, which includes sample pretreatment protocols such as filtration, analyte cleanup, or analyte preconcentration. However, also the integration of corresponding microfabricated elements is described. Filtration was achieved by porous membranes or arrays of thin channels preventing particulates to enter the analytical device. Analyte preconcentration in combination with removal of other sample constituents is achieved by solid-phase extraction modules, which are either capillaries or beads coated with a suitable adsorbent, such as a Cl 8 phase originating from coating with octa-decyltrimethoxysilane, from which the analyte is... 

Generally, samples are injected in the chromatographic system without any dilution or pretreatment step, using the split mode (i.e., with sample division), which is suitable for the analysis of the major compounds in beverages.When the objective of analysis is the determination of compounds present in small quantities (p.g/L), some extraction and/or concentration step is necessary, followed by the sample injection in the spMess mode (without sample division). This last sample introduction mode is usually combined with extraction techniques such as liquid-liquid extraction (LLE), solid-phase extraction (SPE), " and solid-phase microextraction (SPME). ... 

Recently, solid phase extraction (SPE) on several stationary phases has been extensively used in the pretreatment of both plant and biological samples. Typically, crude extracts are mixed with appropriate solvents (methanol or ethanol) and the resulting solutions are applied onto the SPE cartridges. The cartridges are next washed with appropriate solvents to take out impurities and, finally, the taxanes are eluted in an optimized recovery solvent. The obtained taxane fraction is evaporated to dryness and, after reconstimtion to solution, an aliquot is analyzed by HPLC. 

The sample pretreatment used to determine procyanidins and their metabolites in plasma samples (from rats) is off-line solid-phase extraction (SPE) with hydrophilic-lipophilic balanced (HLB) copolymer. Both cartridges (60 mg) [31,32] and microelution SPE plates (pSPEs) (2 mg) [33,36,37] have been used as the device format. For the analysis of tissues (also from rats), such as the liver, brain, aorta artery, and adipose tissue, these were first freeze-dried and then pretreated by off-line Ll.F. (with the solution made up of methanol, water, and phosphoric acid) followed by pSPE [35-37]. The use of two sample pretreatments (LLE and pSPE) is due to the complexity of the tissue sample compared with the biofluid plasma sample. The extraction recoveries (%Rs) for determining the procyanidins catechin, epicatechin, dimer B2, and trimer in the plasma samples by pSPE [33] and SPE [31] were higher... 

The small inner diameter of the separation capillary used in CE implies a short optical pathway, and the consequent poor concentration sensitivity when conventional UV detectiOTi is used. To overcome this drawback several techniques have been developed some of them consist in application of general approaches that are not specifically addressed to CE analysis of alkaloids. One is the use of LIF detector for analysis of alkaloids with native fluorescence [68, 69] or after their off-line derivatization [64, 88, 112]. Sample pretreatment, a second major approach, is popularly employed in combination with sample extraction and can be conveniently applied in analysis of alkaloids because they can be easily retained in cationic-exchange sorbents in solid-phase extraction (SPE) mode [113, 114]. It may be interesting to focus on more specific aspects to detect very low levels of analytes using limited amoimts of samples to this regard chemiluminescence reactions and the use of online preconcentration methods will be considered. 

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