Solid-phase extraction dual phases

Peterson DS, Rohr T, Svec FK, Frechet JMJ (2003) Dual-function microanalyt-ical device by in situ photolithographic grafting of porous polymer monolith integrating solid-phase extraction and enzymatic digestion for peptide mass mapping. Anal Chem 75 5328... 

Gustavson et al. (2000) developed a convenient and novel solid phase extraction (SPE) method for the removal of methyl oleate from SPMD dialysates containing PAHs. A small SPE column (1 g or 0.5 g) containing a dual-zone silica (normal phase)-based restricted-access sorbent (Diazem, Midland, MI, USA) is used for the separation. The capacity of this sorbent to remove methyl oleate is about 1.8% (lipid/sorbent wt wt ). The PAHs are eluted with 19 mL of hexane and methylene chloride (97 3 VV ) and recoveries of all PAHs are typically >72%. 

When using PFT with a neutral selector, it is quite difficult to avoid any entrance of the chiral selector into the ionization source, particularly at a high pH, where EOF is important. The use of BGE at low pH and/or coated capillary to minimize EOF is therefore mandatory. However, the coaxial sheath gas, which generally assists the ionization process, leads to an aspirating phenomenon of the chiral selector in the MS direction. Javerfalk et al. were the first to apply PFT with a neutral methyl-/i-CD for the separation of racemic bupivacaine and ropivacaine with a polyacrylamide-coated capillary and an acidic pH buffer (pH 3). Cherkaoui et al. employed another neutral CD (HP-/1-CD) with a PVA-coated capillary for the analysis of amphetamines and their derivatives. To prevent a detrimental aspiration effect, analyses were carried out without nebulization pressure. Numerous other studies presented excellent results such as the enantioselective separation of adrenoreceptor antagonist drugs using tandem mass spectrometry (MS/MS) the separation of clenbuterol enantiomers after solid-phase extraction (SPE) of plasma samples or the use of CD dual system for the simultaneous chiral determination of amphetamine, methamphetamine, dimethamphetamine, and p-hydroxymethamphetamine in urine. 

Peterson, D.S. Rohr, T. Svec, F. Frechet, J.M.J. Dual-function Microanalyti-cal Device by In Situ Photolithographic Grafting of Porous Polymer Monolith Integrating Solid-Phase Extraction and Enzymatic Digestion for Peptide Mass Mapping, Anal. Chem. 75, 5328-5335 (2003). 

The restricted-access solid-phase extraction may work in dual mode when it combines size exclusion and reversed-phase partitioning to isolate and clean up complex matrices such as serum, blood, and plasma (Haginaka, 1991). In this case, it is an internal-surfaced reversed phase (ISRP), as shown in Figure... 

Extract with DCM. Concentrated and loaded onto a dual-stage carbon sorbent trap. SPED Extract with DCM or solid-phase extraction on two adsorbents (C8 and activated carbon), and elute with ethanol Extract with DCM. Wastewater (CLLE)... 

Reedy CR, Hagan KA, Strachan BC, Higginson JJ, Bienvenue JM, Greenspoon S A, Ferrance JP, Landers JP (2010) Dual-domain microchip-based process for volume reduction solid phase extraction of nucleic acids from dilute, large volume biological samples. Anal Chem 82 5669-5678... 

Benijts, T., Lambert, W., and De Leenheer, A. (2004) Analysis of multiple endocrine disrupters in environmental waters via wide-spectrum solid-phase extraction and dual-polarity ionisation LC-ion trap MS/MS. Analytical Chemistry 76, 704-711. 

The phthalate esters can also be determined by GCECD after an appropriate solvent extraction from aqueous or solid samples. USEPA Method 8061 lists 16 phthalate esters (13). Solid-phase extraction using C18 membrane disks can be used for aqueous samples, but the pH must be maintained between 5 and 7 to prevent hydrolysis of the phthalate esters. Solids or soils can be extracted by sonication or Soxhlet extraction using 1-1 methylene chloride-acetone. GPC or the Florisil cleanup may be necessary. Extreme care must be taken not to contaminate samples with phthalate esters that are ubiquitous in the laboratory. The solvent needs to be exchanged to hexane. Two megabore capillary columns that are connected by a Y in parallel are recommended for separation. Detection is accomplished by dual ECDs. The conditions for the GC are listed in Table 15.13. 

Cardwell and Christophersen reported a dual channel FI system with amperometric detection for the determination of ascorbic acid and sulfur dioxide in wines and fruit juices (Cardwell and Christophersen, 2000). Here, the ascorbic acid was detected at a glassy carbon electrode polarized at 0.42 V (vs. Ag/AgCl), whereas the sulfur dioxide was detected at a Pt electrode polarized at 0.90 V (vs. Ag/AgCl) after separation of the analytes by a gas diffusion unit. The determination of ascorbic acid showed a linear range between 3 and 50 mg L with an FOD of 1.5 mg L for sulfur dioxide the linear range was between 0.25 and 15 mgF i and an FOD of 0.05 mgF" was obtained. The sample frequency achieved with the system was 30 h b The proposed method showed a good agreement with a reference method in the results obtained for white wines and juice samples, while for red wines and sweet wines an extraction procedure of the analytes by solid-phase extraction was required. 

After centrifugation, the supernatant was loaded onto a graphite carbon/PSA (primary secondary amine) dual-layer, solid-phase extraction column and eluted with 50 mL of acetonitrile/toluene (3 1). After the eluate was concentrated under reduced pressure, it was dissolved (Ig/mL) in 10 mL of acetonitrile/w-hexane to give the test solution (Hollosi et al, 2013). 

The identification of synthetic colorants (pure or mixtures) in foods is usually carried out using spectrophotometry but the resolution of complex mixtures in food requires a previous separation of extract components by SPE and chromatographic techifiques. Dual wavelength, solid phase, and derivative spectrophotometric methods combined with chemometric approaches have been used. ... 

Based on these electrochemical studies we developed a method for the quantitation of ajmalicine and catharanthine in cell cultures. These alkaloids were extracted from freeze-dried cells and purified by the solid-phase procedure described by Morris et al. (1985), except that ethanol was used as the extracting solvent instead of methanol. A dual-electrode coulometric cell was used in the screen mode. The potential of the first electode was set at +0.2 V (vs. Pd), which was at the base of catharanthine s voltammogram. The alkaloids were detected by the second electrode at +0.8 V, as this offered the best S/N ratio. Higher potentials led to lower S/N ratio, since the background current and noise started to increase exponentially above +0.85 V, due to the oxidation of water. The mobile phase was purified by a guard cell between the pump and injector. The guard cell operated at +0.8V. 

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