Extraction on-line

Figure 2.21 shows the on-line extraction gas chromatogram of 2.25 ml of water spiked at 5 ppb levels with 14 different organic pollutants (40). In this case, the authors concluded that wall-coated open tubular traps (thick-film polysiloxane phases) can be used for the on-line extraction of organic compounds from water. However, when using swelling agents such as pentane, non-polar analytes can be trapped quantitatively, while for more polar compounds chloroform is the most suitable solvent. 

Figure 2.21 A gas cluomatogram of a sample of river water (2.25 ml) spiked at 5 ppb levels with 1, toluene 2, ethylbenzene 3, methoxybenzene 4, p-dichlorobenzene 5, dimethylphe-nol 6, dimethylaniline 7, chloroaniline 8, indole 9, dichlorobenzonitrile 10, tiichlorophe-nol 11, dinitrobenzene 12, tiifluranil 13, atrazine 14, phenantlnene. Reprinted from Journal of High Resolution Chromatography, 16, H. G. J. Mol et al., Use of open-tubular tapping columns for on-line extraction-capillary gas cluomatography of aqueous samples , pp. 413-418, 1993, with permission from Wiley-VCH.

Although on-line sample preparation cannot be regarded as being traditional multidimensional chromatography, the principles of the latter have been employed in the development of many on-line sample preparation techniques, including supercritical fluid extraction (SFE)-GC, SPME, thermal desorption and other on-line extraction methods. As with multidimensional chromatography, the principle is to obtain a portion of the required selectivity by using an additional separation device prior to the main analytical column. 

The effect of the variation in mobile phase composition can be overcome by the use of post-column on-line extraction to remove water from the mobile phase and thus produce a 100% organic mobile phase and this is also likely to bring about an increase in overall sensitivity. 

In the last several years, on-line extraction systems have become a popular way to deal with the analysis of large numbers of water samples. Vacuum manifolds and computerized SPE stations were all considered to be off-line systems, i.e., the tubes had to be placed in the system rack and the sample eluate collected in a test-tube or other appropriate vessel. Then, the eluted sample had to be collected and the extract concentrated and eventually transferred to an autosampler vial for instrumental analyses. Robotics systems were designed to aid in these steps of sample preparation, but some manual sample manipulation was still required. Operation and programming of the robotic system could be cumbersome and time consuming when changing methods. 

In summary, the development of materials for the extraction of pesticides from water samples has progressed from simple liquid-liquid extraction for the principal active compound to sophisticated SPE media capable of exclusively trapping the target pesticide and metabolites selectively. The development of alkyl bonded phase silica cartridges and extraction disks combined with on-line extraction techniques is currently the principal means used for the extraction and trace enrichment of pesticides and metabolites from water. 

In on-line extraction the process is coupled directly ( hyphenated ) to the analytical technique used for further analysis of the extract (either spectroscopy or, more frequently, chromatography, because of the limited selectivity of extraction). Common examples include SFE-GC, SFE-SFC, SFE-HPLC, SFE-FTIR,... 

HPLC-PDA-MS) are already being used. Although HPLC-NMR-MS provides a very powerful approach for compositional and structural analysis, it by no means represents the limit of what is possible in terms of hyphenation. On-line extraction and the attachment of multiple detectors (e.g. IR, F) make the technique even more powerful. Other analytical laboratories such as TG-DTA-DSC-FTIR, TD-CT/Py/GC-MS/FTIR and HPLC-UV/NMR/IR/MS have been put to work, but do not represent practical solutions for routine polymer/additive analysis. 

SFE may also be coupled to GC and HPLC systems [28] for a simple on-line extraction and analysis system. Lycopene is determined in food products such as tomatoes and tomato products, using SFE coupled to HPLC with an HPLC column used for trapping and analysis. The method is short, requires small sample amounts, and has good linearity and sensitivity. Because the entire system is closed, there is little chance for the lycopene to degrade. 

Takino, M., Daishima, S., and Nakahara, T. (2003). Determination of perfluorooctane sulfonate in river water by liquid chromatography/atmospheric pressure photoionization mass spectrometry by automated on-line extraction using turbulent flow chromatography. Rapid Commun. Mass Spectrom. 17, 383—390. 

Souverain, S., Rudaz, S., and Veuthey, J. L. (2004). Matrix effect in LC-ESTMS and LC-APCTMS with off-line and on-line extraction procedures. /. Chromatogr. A 1058, 61 — 66. 

Zeng, H. Deng, Y. Wu, J. T Fast analysis using monolithic columns coupled with high-flow on-line extraction and electrospray mass spectrometric detection for the direct and simultaneous quantitation of multiple components in plasma. 

Quest Diagnostics use an LC-MS/MS panel for diagnosing cortisol-related disorders by urine analysis. This panel was designed to diagnose Cushings syndrome and the hypertensive conditions AME and GRA. The panel quantifies cortisone, cortisol, 6/j-hydroxycorlisol and 18-hydroxycortisol (18-OHF). The Quest analysis uses 2H4 cortisol as an internal standard and HTLC for on-line extraction. This panel has replaced the RIA and HPLC methods previously used by this commercial laboratory. Another recent publication describes MS/MS of cortisone and cortisol in serum using APPI and similar conditions and MRM transformations to those listed above [43]. 

Quest Diagnostics have established a routine system for testosterone, which has now replaced their other methods of analysis (Goldman et al., poster, US Endocrine Society meeting, San Diego, 2005). The analysis is carried out on a Thermofinnigan TSQ Quantum Ultra operated with an APCI source in the positive-ion mode. They use two transitions, 289—>109 and 289—>97, for the analyte and 294—>112 and 294—> 99 for the 2H5-labeled internal standard. On-line extraction and short retention times allow them to assay several thousand samples per month per instrument, making it cost-effective in spite of the high cost of instrumentation. 

Utilize on-line extraction and separation techniques to minimize work-up procedures and increase throughput. 

Rauh M, Groschl M, Rascher W, Dorr HG (2006) Automated, fast and sensitive quantification of 17 alpha-hydroxy-progesterone, androstenedione and testosterone by tandem mass spectrometry with on-line extraction. Steroids 71 450-458... 

DeMaio, W., Di Bussolo, J. M., Lloyd, T., Kandoussi, H., and Talaat, R. E. (2005). On-line extraction and concentration techniques using turbulent-flow hplc to analyze human... 

Hsieh, S., Tobien, T., Koch, K., and Dunn, J. (2004). Increasing throughput of parallel on-line extraction liquid chromatography/electrospray ionization tandem mass spectrometry system for GLP quantitative bioanalysis in drug development. Rapid Commun. Mass Spectrom. 18 285-292. 

Van Eeckhout, N., Perez, J. C., and Van Peteghem, C. (2000). Determination of eight sulfonamides in bovine kidney by liquid chromatography/tandem mass spectrometry with on-line extraction and sample clean-up. Rapid Commun. Mass Spectrom. 14 2331-2338. 

H. G. J. Mol, H.-G. Janssen and C. A. Cramers, Use of open-tubular trapping columns for on-line extraction-capillary gas chromatography of aqueous samples , J. High Resolut. Chromatogr. 16 413-418 (1993). 

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