In-line SPE

Figure 11.18 Schematic diagram of an in-line SPE unit for CE using (a) polyester wool frits to hold the sorbent, or (b) a paiticle-loaded membrane. Reprinted from Journal of Capillary Electrophoresis, 2, A. J. Tomlinson and S. Naylor, Enhanced performance membrane preconcenti ation-capillary electrophoresis-mass spectiometi y (mPC-CE-MS) in conjunction with ti ansient isotachophoresis for analysis of peptide mixtures, pp 225-233, 1995, with permission from ISC Teclmical Publications Inc.

Rosiglitazone 9, an agonist of peroxisome proliferator activated receptor-y (PPARy), is a recently introduced antihyperglycemic thiazolidinedione effective in the treatment of noninsulin dependant diabetes mellitus (type II diabetes). A seven-step synthesis was developed (Scheme 3), which utilised supported reagents in combination with in-line SPE purifications. The introduction of the pyridine moiety provided a convenient molecular handle by which to purify the molecule throughout the synthesis. Notably, the overall yield (46%) for this synthesis was higher than the yield reported in the initial shorter solution-phase synthesis (31%). ... 

Mass spectrometry is another detection technique widely used in neuropeptide analysis. Concentration sensitivities in CE-MS do not reach those obtained by CE-LIF nevertheless, tedious derivatization procedures are avoided. In addition, CE-MS has proven to be a powerful tool for structure elucidation as illustrated by the investigation of the in vivo metabolic fate of peptide E by Caprioli s group [12]. After microdialysis and in-line SPE, neuropeptides migrating out of the electrophoresis capillary were deposited directly onto a precoated cellulose target used in matrix-assisted laser desorption-time of flight (MALDI-TOF) MS subsequently. Structural information is then obtained along with the mass of the peptide(s). 

Fe Multi-vitamin tablets UV irradiation for sample dissolution and thermal digestion using a 100 W tungsten lamp, HC1 and h2o2 UV-Vis 100—500 pg per tablet (1 g) Multi-commuted flow system in-line SPE for analyte separation/ concentration as chlorocomplex analogous flow system for the determination of Cu and Zn by FAAS [426]... 

N-methyl- carbamates Contaminated soils and fruits (apples, pears, cucumbers) Ultrasound-assisted extraction Fluorimetry 12 ng g 1 Unsegmented flow system in-line [433] filtration in-line SPE HPLC postcolumn derivatisation... 

Gold, thallium Coal fly ash, ores Benzene UV-Vis 0—5 mg I. 1 (for both analytes) C-FIA in-line SPE for [467] separating the analytes as chloro-complexes membrane for phase separation... 

As the sorption and elution steps are accomplished by changing the nature or the concentrations of the solutions involved, the formation of concentration gradients is unavoidable. These gradients can give rise to occurrences of the Schlieren effect [206], and this is the main reason why detection techniques less affected by the Schlieren effect, e.g., atomic absorption/emission spectrometry, are most commonly used in flow systems with in-line SPE. 

Different manifold geometries have been proposed for implementing in-line SPE in flow analysis, generally involving the placement of a minicolumn before, at or after the sample introduction port. Alternatively, by integrating SPE within the detection unit, moving beads, hyphenated techniques and/or commutation facilities can be exploited, as discussed at the end of this section. 

FIGURE 8.15 Didactic representation of a flow system with in-line SPE prior to sample introduction. S = sample C = sample carrier stream R = reagent Rc — coiled reactor D = detector box — mini-column black ellipse = depleted sample. Air stream and de-bubbler not shown, as the representation also holds for unsegmented flow analysis. 

This paper deseribes a rapid and versatile on-line-SPE LC-MS/MS method developed for the determination of various pestieides and tlieir metabolites in water. 28 pestieides, ineluding various triazines, phenylureas, organophosphorous eompounds and other speeies, were seleeted for systematie investigations. 

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.

Figure 11.5 Chromatograms of plasma samples obtained with fully automated on-line SPE-LC (a) dmg-ffee human plasma (b) human plasma spiked with omeprazole (100 ng/ml) and phenacetin (internal standard 1000 ng/ml). Reprinted from Journal of Pharmaceutical and Biomedical Analysis, 21, G. Garcia-Encina et al., Validation of an automated liquid chromatograpliic method for omeprazole in human plasma using on-line solid-phase exti action, pp. 371 - 382, copyright 1999, with permission from Elsevier Science.

In principle, on-line SPE-LC can be automated quite easily as well, for instance, by using Such programmable on-line SPE instrumentation as the Prospekt (Spark Holland) or the OSP-2 (Merck) which have the capability to switch to a fresh disposable pre-column for every sample. Several relevant applications in the biomedical field have been described in which these devices have been used. Eor example, a fully automated system comprising an autosampler, a Prospekt and an LC with a UV... 

LC-MS with on-line SPE using a RAM pre-column with an internal ODS phase was described by van der Hoeven et al. (95) for the analysis of cortisol and prednisolone in plasma, and arachidonic acid in urine. The samples were injected directly and the only off-line pretreatment required was centrifugation. By using the on-line SPE-LC-MS system, cortisol and related compounds could be totally recovered and quantified in 100 p.1 plasma within 5 min with a typical detection of 2 ng/ml (Figure 11.6(b)). The RAM-type of sorbents, in which the outer surface of the particles is covered with aj-acid glycoprotein, also appear to be useful for direct SPE of... 

On-line SPE-LC has been widely used in environmental analysis to solve the problems caused by the low concentrations of the analytes to be detected and also to automate the analysis (42-44). 

This set-up, or a very similar one, has been used to determine different group of pollutants in environmental waters (45, 83, 93). For example, with 10 ml of sample the limits of detection of a group of pesticides were between 2 and 20 ng 1 (92) in tap and river water, with this system being fully automated. Figure 13.19 shows the chromatograms obtained by on-line SPE-GC-MS under selected ion-monitoring conditions of 10 ml of tap water spiked with pesticides at levels of 0.1 pig 1 (92). 

Figure 13.19 Chromatograms obtained by on-line SPE-GC-MS(SIM) of (a) 10 ml of tap water spiked with pesticides at levels of 0.1 ng 1 (b) 10 ml of a sample of unspiked tap water. Peak identification foi (a) is as follows 1, molinate 2, a-HCH 3, dimethoate 4, simazine 5, ati azine 6, y-HCH 7, S-HCH 8, heptachloi 9, ametiyn 10, prometiyn 11, fen-itrothion 12, aldrin 13, malatliion 14, endo-heptachlor 15, a-endosulfan 16, teti achlor-vinphos 17, dieldrin. Reprinted from Journal of Chromatography, A 818, E. Pocumll et al., On-line coupling of solid-phase exti action to gas cliromatography with mass specti ometiic detection to determine pesticides in water , pp. 85-93, copyright 1998, with permission from Elsevier Science.

Crescenzi et al. developed a multi-residue method for pesticides including propanil in drinking water, river water and groundwater based on SPE and LC/MS detection. The recoveries of the pesticides by this method were >80%. Santos etal. developed an on-line SPE method followed by LC/PAD and LC/MS detection in a simultaneous method for anilides and two degradation products (4-chloro-2-methylphenol and 2,4-dichlorophenol) of acidic herbicides in estuarine water samples. To determine the major degradation product of propanil, 3,4-dichloroaniline, the positive ion mode is needed for atmospheric pressure chemical ionization mass spectrometry (APCI/MS) detection. The LOD of 3,4-dichloroaniline by APCI/MS was 0.1-0.02 ng mL for 50-mL water samples. 

Immunosorbents have also found applicability in on-line SPE analysis. An antibody is immobilized on to a silica support and used as an affinity ligand to retain targeted analytes. Components not recognized by the antibody are not retained and some degree of selectivity is attained. Recoveries of 87-103% were obtained for atrazine, simazine, DEA, propazine, and terbuthylazine at the 0.2 xgL concentration level when using immunosorbent SPE (80 mg silica and 2 mg anti-atrazine and anti-chlortoluron antibodies) on-line with LC/APcI-MS however, this method is not applicable to DIA (0% recovery). This compound may be better retained when using an... 

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