Restricted solid phase extraction

Van der Hoeven, R.A. et al. 1997. Liquid chromatography/mass spectrometry with on-line solid-phase extraction by a restricted-access C18 precolumn for direct plasma and urine injection. J. Chromatosr. A. 762 193-200. 

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%. 

The applicability of the APCI interface is restricted to the analysis of compounds with lower polarity and lower molecular mass compared with ESP and ISP. An early demonstration of the potential of the APCI interface is the LC-APCI-MS-MS analysis of phenylbutazone and two of its metabolites in plasma and urine (128). Other applications include the LC-APCI-MS analysis of steroids in equine and human urine and plasma (129-131), the determination of six sulfonamides in milk samples after a simple solid-phase extraction and LC separation (132), of tetracyclines in muscle at the 100 ppb level (133), of fenbendazole, oxfendazole, and the sulfone metabolite in muscle at the 10 ppb level, and of five thyreostats in thyroid tissue at the 1 ppm level (134). 

Unlike clenbuterol, salbutamol is a difficult compound to analyze due to its particular chemical attributes. It is a basic compound subjected to protein binding poor recoveries are obtained especially when protein precipitation techniques are used to prepare the extracts (145). In addition, salbutamol is charged at all pH values and does not readily lend itself to simple, specific back-extracting procedures. This severely restricts the options of sample cleanup. However, a Subtilisin protease digestion step followed by acid clarification and solid-phase extraction has been suggested (146) as an adequate extraction and cleanup procedure prior to the end-point determination of salbutamol by an enzyme immunoassay (139) based on the cross-reactivity of anticlenbuterol antibodies. 

Starting with a description of the analytical challenge in Chapter 19, the third part, which is devoted to analytical attitudes, proceeds with a detailed description in Chapter 20 of modern sample preparation procedures including solid-phase extraction, matrix solid-phase dispersion, use of restricted-access media, supercritical fluid extraction, and immunoaffinity cleanup. Flexible derivatization techniques including fluorescence, ultraviolet-visible, enzymatic, and photochemical derivatization procedures are presented in Chapter 21. 

R. A. M. van der Hoeven, A. I. P. Hofte, M. Frenay, H. Irth, U. R. Tjaden, I. van der Greef A. Rudolphi, K.-S. Boos, G. Marko Varga and L. E. Edholm, Liquid chromatography-mass spectrometry with on-line solid-phase extraction by a restricted-access C18 precolumn for direct plasma and urine injection ,. /. Chromatogr. A 762 193-200(1997). 

K. S. Boos and C. H. Grimm, High performance liquid chromatography integated with solid-phase extraction in bioanalysis using restricted access precolumn packings , Trends Anal. Chem. 18 175-180 (1999). 

Capillary electrophoresis (CE) coupled to MS has the advantage of high resolution and soft ionization for biomolecules, which may be used to differentiate post-translational modifications and variants of intact proteins and oligonucleotides. Different modes of CE (capillary zone electrophoresis, capillary isoelectric focusing, capillary electrochromatography, micellar electrokinetic chromatography, nonaqueous capillary electrophoresis) to MS as well as online preconcentration techniques (transient capillary isotachophoresis, solid-phase extraction, membrane preconcentration) are used to compensate for the restricted detection sensitivity of the CE methodology [77, 78]. 

Yamamoto, E., Takakuwa, S., Kato, T., Asakawa, N. Sensitive determination of aspirin and its metabolites in plasma by LC-UV using on-line solid-phase extraction with methylcellulose-immobilized anion-exchange restricted access media. J. Chromatogr. B 846, 132-138 (2007)... 

After leaving the preparation process, the flakes (or collets) are delivered to the solvent extraction operation. As this process typically uses a flammable solvent (and is classified as a hazardous flammable environment), the operation is usually somewhat removed from other facilities, and access to the controlled area is restricted. Figure 5 illustrates the typical unit operations associated with solvent extraction, which include extraction, solvent distillation, and liquid-phase recovery. Upon discharge from the extractor, solid-phase extracted material is desolventized, toasted, dried, and cooled prior to meal finishing. 

Solid-phase extraction (SPE), which can be done off-hne or on-line by means of cartridges, cartridge columns, or extraction disks (Ch. 11.6.4), and eventually by using special packing materials, such as restricted access materials (RAM) or turbulent-flow chromatography (TFC) (Ch. 11.6.5). 

Solid-phase extraction (SPE) is an alternative to LLE. In SPE the analytes are partioned between a solid and a liquid [57, 58], Generally, interfering compounds are rinsed off the solid adsorbent and the analytes are then desorbed with an eluting solvent [58], A range (e.g., normal-phase, reversed-phase, ion exchange, restricted access) of sorbents and formats are available for SPE and the SPE systems are easy to automate [59, 60], In order to accomplish the isolation of the products from the fermentation matrix, both SPE and LLE were evaluated for use in papers I and II. 

Three recently introduced on-line extraction techniques have been applied to biological samples. These techniques involve direct injection with restricted access media [11,12], turbulent flow chromatography [13], and on-line solid-phase extraction. 

FIGURE 11.1 A generalized flow scheme that indicates the fundamental elements of LC-MS-based bioanalysis. Abbreviations LLE = liquid-liquid extraction SPE = solid-phase extraction RAM = restricted-access media TEC = turbulent flow liquid chromatography API = atmospheric-pressure ionization APCI = atmospheric-pressure chemical ionization ESI = electrospray ionization SQMS = single-quadrupole mass spectrometry TQMS = triple-quadrupole mass spectrometry TOF = time-of-flight Q-TOF = quadrupole TOF. (Reprinted from Ackermann et al. [4], with permission from John Wiley Sons, Inc.)... 

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... 

Figure 12,6. Restricted-access solid-phase extraction. [Reproduced with permission from Haginaka (1991).]...

Onnerfjord, P., Barcelo, D., Emneus, J., and Gorton, L., and Markovarga, G. 1996, Online solid-phase extraction in liquid chromatography using restricted access precolumns for the analysis of s-triazines in humic-containing waters, J. Chromatog., 737 35-45. 

Many different sample preparation techniques are available to the drug discovery scientist. Off-line sample preparation procedures include protein precipitation, filtration, dilution followed by injection, liquid-liquid extraction (LLE), and solid-phase extraction (SPE). Typically, these procedures are performed in an automated, high-throughput mode that features a 96-well plate format. Online sample preparation procedures include SPE and turbulent flow chromatography (TFC) with conventional chromatographic media or restricted access media (RAM). These online approaches are often simple and easy to automate. 

The sample introduction system must be capable of introducing a known and variable volume of sample solution reproducibly into the pressurized mobile phase as a sharp plug without adversely affecting the efficiency of the column. The superiority of valve injection has been adequately demonstrated for this purpose and is now universally used in virtually all modern instruments for both manual and automated sample introduction systems [1,2,7,31,32]. Earlier approaches using septum-equipped injectors have passed into disuse for a several reasons, such as limited pressure capability, poor resealability, contamination of the mobile phase, disruption of the column packing, etc., but mainly because they were awkward and inconvenient to use compared with valves. For dilute sample solutions volume overload restricts the maximum sample volume that can be introduced onto the column without a dramatic loss of performance. On-column or precolumn sample focusing mechanisms can be exploited as a trace enrichment technique to enhance sample detectability. Solid-phase extraction and in-column solid-phase microextraction provide a convenient mechanism for isolation, concentration and matrix simplification that are easily interfaced to a liquid chromatograph for fully or semi-automated analysis of complex samples (section 5.3.2). 

An evaluation of the scientific literature reveals that over 500 papers on veterinary drug residue analysis were published in the 5-year period of 2005-2009. Liquid extraction (LE) and liquid-solid extraction (LSE) were found to be very popular sample treatment techniques that were used in 30% and 60% of the reported studies, respectively. Here, LE includes all liquid-based approaches such as liquid-liquid extraction (LLE), extrelut liquid-liquid extraction, liquid-liquid micro-extraction, and pressurized liquid extraction (PLE). LSE includes solid phase extraction (SPE) and all other sorbent-based extraction procedures, such as solid phase micro-extraction (SPME), stir bar sorptive extraction (SBSE), restricted-access materials (RAM), turbulent-flow chromatography (TEC), dispersive SPE (dSPE), and matrix solid phase dispersion... 

Boos, K.S. Fleischer, C.T. Multidimensional on-line solid-phase extraction (SPE) using restricted access materials (RAM) in combination with molecular imprinted pol5uners (MIP). Fresenius J. Anal. Chem. 2001, 371, 16-20. 

HPLC-UV-NMR is a powerful technique for the identification and characterization of flavonoids. However, there are drawbacks, as NMR remains rather insensitive because of the need for solvent suppression, which has restricted the observable NMR range. Recently, two major research developments in HPLC-UV-NMR are post-column solid-phase extraction (HPLC-UV-SPE-NMR) and combination of HPLC-UV-SPE with capillary separations and NMR detection [89]. A post-column treatment of analyte focusing and multiple trapping through a SPE has solved the problem of sensitivity and solvent suppression. The separation and elucidation of three C-methylated flavanones and five dihydrochalcones from Myrica gale seeds have been achieved by HPLC-DAD-SPE-NMR and... 

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