On-line extraction procedures

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. 

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

We report on a number of on-line chemical procedures which were developed for the study of short-lived fission products and products from heavy-ion interactions. These techniques combine gas-jet recoil-transport systems with I) multistage solvent extraction methods using high-speed centrifuges for rapid phase separation and II) thermochromatographic columns. The formation of volatile species between recoil atoms and reactive gases is another alternative. We have also coupled a gas-jet transport system to a mass separator equipped with a hollow cathode- or a high temperature ion source. Typical applications of these methods for studies of short-lived nuclides are described. 

As an alternative, immunoaffinity procedures have been developed to selectively extract PAHs from environmental samples. Thomas and Li62 demonstrated the greater efficiency of immunoaffinity methods in comparison with conventional extraction procedures. Bouzige et al.48 prepared an immunosorbent for use in an on-line analytical procedure, followed by liquid chromatography coupled to fluorescence detection, to monitor surface water samples. The sensitivity of the fluorescence detection in combination with the selectivity of the immunosorbent (IS) extraction enabled PAH compounds to be detected at levels between 2 and 10 ng I. 

The recovery experiment carried out for this assay resembles somehow the sum of two potential effects The loss of compound during the sample preparation process (in this case on-line extraction) and a potential matrix effect during sample analysis. However, since an online sample clean up procedure is used here, these two potential effects cannot be separated in the usual way (One experiment would be the comparison of a processed spiked plasma sample with a blank plasma sample spiked post sample processing in order to determine the recovery of the sample preparation step. In a second experiment, again a processed blank plasma sample would be spiked post processing and the result would be compared with the response of a spiked solvent sample in order to reveal a potential matrix effect during analysis). 

Anions of another group were derivatized with formation of gaseous chemiluminescing species. Chemical reaction - gas extraction has been used with chemiluminescence detection in the stream of canier gas in on-line mode. Rate of a number of reactions has been studied as well as kinetic curves of extraction of gaseous products. Highly sensitive and rapid hybrid procedures have been developed for the determination of lO, BrO, CIO, CIO, NO,, N03, CrO, CIO, Br, T, S, 803 with detection limits at the level of pg/L, duration of analysis 3 min. 

Presently, the on-line coupling of NPLC and GC via heart-cutting is an established procedure which has been used successfully for several bioanalytical applications. Obviously, dfrect analysis of aqueous samples is not possible by NPLC, and therefore, a solvent switch by a sample pretreatment step (e.g. liquid-liquid extraction or SPE) is always requfred when biological samples are analysed by NPLC-GC. 

The most widely employed techniques for the extraction of water samples for triazine compounds include liquid-liquid extraction (LLE), solid-phase extraction (SPE), and liquid-solid extraction (LSE). Although most reports involving SPE are off-line procedures, there is increasing interest and subsequently increasing numbers of reports regarding on-line SPE, the goal of which is to improve overall productivity and safety. To a lesser extent, solid-phase microextraction (SPME), supercritical fluid extraction (SEE), semi-permeable membrane device (SPMD), and molecularly imprinted polymer (MIP) techniques have been reported. 

There are basically three methods of liquid sampling in GC direct sampling, solid-phase extraction and liquid extraction. The traditional method of treating liquid samples prior to GC injection is liquid-liquid extraction (LLE), but several alternative methods, which reduce or eliminate the use of solvents, are preferred nowadays, such as static and dynamic headspace (DHS) for volatile compounds and supercritical fluid extraction (SFE) and solid-phase extraction (SPE) for semivolatiles. The method chosen depends on concentration and nature of the substances of interest that are present in the liquid. Direct sampling is used when the substances to be assayed are major components of the liquid. The other two extraction procedures are used when the pertinent solutes are present in very low concentration. Modem automated on-line SPE-GC-MS is configured either for at-column conditions or rapid large-volume injection (RLVI). 

Klink [135] recently discussed sample preparation procedures for LC-MS. SPE can be so well integrated into the concept of LC-MS, that in many automated applications no clear distinction exists between SPE and LC [135]. In on-line LC-MS mode, the possibilities for changing the eluent are rather limited, because of the tolerance of the eluent for the interface. Moreover, the conventional gradient mode may lead to strong fluctuations in the response of the MS detector. Here the off-line mode, using SPE for concentration followed by selective elution, enables very far-reaching preseparation, due to the differences in the polarity of the eluents applied and their mixtures. Although the overall benefits of SPE for LC-MS applications are positive, extracts... 

Sample preconcentration was performed by means of an automated on-line SPE sample processor Prospekt-2 (Spark Holland, Emmen, The Netherlands). Oasis HLB cartridges (Waters, Barcelona, Spain) were used to preconcentrate cannabi-noids present in the water samples whereas isolation of the rest of the compounds was done in PLRPs cartridges (Spark Holland). Before extraction, influent samples were diluted with HPLC water (1 9, v/v) to reduce matrix interferences and to fit some analyte concentrations, e.g., cocaine (CO) and benzoylecgonine (BE), within the linear calibration range. A sample volume of 5 mL was spiked with the internal standard mixture (at 20 ng/L) in order to correct for potential losses during the analytical procedure, as well as for matrix effects. Elution of the analytes to the LC system was done with the chromatographic mobile phase. 

Immunoaffinity procedures can be performed either on-line or off-line, and can be coupled to chromatographic systems [ 118,119] or even to immunoassays [120]. Many examples can be found in the literature regarding the use of immunoaffinity extraction of drugs and pharmaceuticals from biological matrices, as well as of organic pollutants such as pesticides from environmental samples [115,121-124]. 

The complex composition of aqueous environmental sample matrices, especially sewage and marine water samples, and the low concentrations in which the surfactants are generally found, have made it necessary to perform an initial stage of concentration and purification of the analytes prior to its analysis. Traditionally, such steps were carried out off-line with procedures based on liquid—liquid extraction (LLE), sublation or steam distillation, followed by chromatographic clean-up steps. 

Before compounds in biological matrices can be analyzed by LC/MS/MS, the samples must undergo a preparation procedure. There are a variety of techniques available for sample preparation including offline sample preparation techniques (liquid-liquid extraction, protein precipitation, and solid phase extraction) and on-line sample preparation... 

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