Sample pretreatment cartridges

Fig. 3. Schematic of the three-layer OnGuard II Ba/Ag/H sample pretreatment cartridge.

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.

Colistin (COL) is a multicomponent antibiotic (polymyxins E) that is produced by strains of inverse Bacillus polymyxa. It consists of a mixture of several closely related decapeptides with a general structure composed of a cyclic heptapeptide moiety and a side chain acetylated at the N-terminus by a fatty acid. Up to 13 different components have been identified. The two main components of colistin are polymyxins El and E2 they include the same amino acids but a different fatty acid (216). A selective and sensitive HPLC method was developed for the determination of COL residues in milk and four bovine tissues (muscle, liver, kidney, and fat). The sample pretreatment consists of protein precipitation with trichloracetic acid (TCA), solid-phase purification on Cl 8 SPE cartridges, and precolumn derivatization of colistin with o-phthalaldehyde and 2-mercaptoethanol in borate buffer (pH 10.5). The last step was performed automatically, and the resulting reaction mixture was injected into a switching HPLC system including a precolumn and the reversed-phase analytical column. Fluorescence detection was used. The structural study of El and E2 derivatives was carried out by HPLC coupled with an electrospray MS. Recoveries from the preseparation procedure were higher than 60%. 

Fig. 4. IC-MS of chloroacetic acid and bromoacetic acid in a matrix containing 1000 mg/1 chloride, without (A) and with (B) sample pretreatment. Peaks 1, chloroacetic acid, 8 mg/l 2, bromoacetic acid, 7 mg/l TIC, total ion chromatogram, m/z 92.5-93.5, extracted ion for chloroacetic acid, m/z 137-139.2, extracted ion for bromoacetic acid. B After sample is passed through OnGuard II Ag/H cartridge.

Finally, the same authors reported the incorporation of electrokinetic injection into their method (31). Little interference was observed in the separation of MPA, EMPA, IMPA, and PMPA in seven different environmental matrices. Limits of detection were reduced to 1—2 xg/L for water samples, which represented an improvement of two orders of magnitude over their previous work using pressure injection. However, a sample cleanup step was necessary to reduce the conductivity of the sample to be compatible with electrokinetic injection. The samples were passed through three pretreatment cartridges arranged in series to remove sulfate, chloride, and cations, respectively. 

Proper sample pretreatment methods are important to reduce or eliminate matrix effects. In this section, advances in sample pretreatment methods in relation to LC-MS quantitative bioanalysis are briefly reviewed (see also Ch. 1.5). Contrary to environmental analysis, where on-line sample pretreatment is often used (Ch. 7.3.2), off-line sample pretreatment appears to be preferred in quantitative bioanalysis. This is partly due to the composition of biological samples, where the presence of especially proteins may cause clogging of the SPE columns, cartridges or disks used, and partly due to the fact that decoupling sample pretreatment and LC-MS analysis generally allows for a higher sample throughput. 

SPE is an important sample pretreatment method in quantitative bioanalysis. As discussed in Ch. 1.5.3, SPE can be performed in single cartridges, in 96-well plate format, and in on-hne mode, either on top of the analytical colunm, or preferably on a precolumn in a column-switching system. 

Sample Pretreatment. Aminonitrazepam was extracted from the postmortem blood by means of a solid-phase isolation on an Extrelut cartridge column (Merck, Darmstadt, FRG). The cartridge was pretreated before use. It was washed with a 1 1 methanol dichloro-methane mixture, dried and treated with ammonia vapor. The postmortem blood sample (1 ml) was diluted with 0.5 ml water and sucked through the cartridge. The column was eluted with 8 ml of diethyl ether. The eluate was evaporated to dryness and redissolved in methanol. 

Rumiantsev, D.O. Ivanova, T.V. Solid-phase extraction of Styrosorb cartridges as a sample pretreatment method in the stereoselective analysis of propranolol in human serum. J.Chromatogr.B, 1995, 674, 301-305... 

There are several commercially available instruments using sorption systems for sample pretreatment. A representative example of those working in a continuous fashion is the Varian AASP (Advanced Automated Sample Processor) [10]. This uses cassettes of ten sorbent cartridges, each of which is packed with 40-50 mg of a particular bonded silica gel. It features three essential differences from typical manual systems, namely the use of lower sample and solvent volumes, the utilization of pressure rather than vacuum and the fact that the liquid emerging from the cartridge is completely eluted to the HPLC system, thereby increasing the sensitivity. Analytical Biochemistry Laboratories (ABC) markets a module (GPC 1002 A) for automated clean-up of residues in extracts by use of a gel-permeation column. 

For solid-phase extraction, the offline procedure, based on sample pretreatment on disposable SPE cartridges, and a totally automated online procedure, based on column switching, have been developed. The column switching procedure involves the use of a polystyrene-divinylbenzene column for sample concentration and cleanup. 

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... 

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