Line coupling

ON-LINE COUPLING OF SPE-HPLC-MS/MS FOR FAST TRACE ANALYSIS OF PESTICIDES IN DRINKING AND SURFACE... 

ON-LINE COUPLING OF CONTINUOUS-FLOW FRACTIONATION OF HEAVY METALS IN ENVIRONMENTAL SOLIDS WITH ATOMIC EMISSION SPECTROMETRY... 

Recently it has been shown that rotating coiled columns (RCC) can be successfully applied to the dynamic (flow-through) fractionation of HM in soils and sediments [1]. Since the flow rate of the extracting reagents in the RCC equipment is very similar to the sampling rate that is used in the pneumatic nebulization in inductively coupled plasma atomic emission spectrometer (ICP-AES), on-line coupling of these devices without any additional system seems to be possible. 

In the present work it has been shown that on-line coupling of flowthrough fractionation in RCC with ICP-EAS detection enables not only the fast and efficient fractionation of trace elements (TE) in environmental solids to be achieved but allows real-time studies on the leaching process be made. A novel five-step sequential extraction scheme was tested in on-line mode. The optimal conditions for the fractionation were chosen. Investigating elution curves provides important information on the efficiency of the reagents used, the leaching time needed for the separation of each fraction, and the potential mobility of HM forms. 

Figure 23.9(b) Typical layout of a line coupling device and carrier equipment (PLCC) showing phase-to-phase coupling... 

K. Groh, On-Line Coupled LC-GC, W. Beitsch, W. G. Jennings and P. Sandra (Series Eds), Hiithig, Heidelberg, Gennany (1991). 

Figure 2.6 Gas cluotnatograni of a 10 ml test sample containing C I4 C26 alkanes in -hexane (about 1 ppb each) the earner gas (H2) inlet pressure was 2.5 bar for a 22 m X 0.32 mm id separation column coupled with a 2 m X 0.32 mm id uncoated precolumn (no vapour exit). Reprinted from Journal of High Resolution Chromatography, 9, K. Grob et al., Concunent solvent evaporation for on-line coupled HPLC-HRGC , pp. 95-101, 1986, with peimission from Wiley-VCH.

K. Grob, C. Walder and B. Schilling, Concuirent solvent evaporation for on-line coupled HPLC-HRGC , 7. High Resolut. Chromatogr. Chromatogr. Commun. 9 95-101 (1986). 

H. G. J. Mol, J. Staniewski, H.-G. Janssen and C. A. Cramers, Use of an open-tubular Capping column as phase-switching interface in on-line coupled reversed-phase liquid clir omatography-capillar y gas clir omatography , 7. Chromatogr. 630 201-212 (1993). 

M.-L. Riekkola, Applications of on-line coupled liquid cliiomatography-gas cliio-matography , J. Chromatogr. 473 315-323 (1989). 

J. Beens and R. Tijssen, An on-line coupled HPLC-HRGC system for the quantitative chai acterization of oil fractions in the middle distillate range , J. Microcolumn Sep. 7 345-354(1995). 

Although SFE and SFC share several common features, including the use of a superaitical fluid as the solvent and similar instrumentation, their goals are quite distinct. While SFE is used mainly for the sample preparation step (extraction), SFC is employed to isolate (chr-omatography) individual compounds present in complex samples (11 -15). Both techniques can be used in two different approaches off-line, in which the analytes and the solvent are either vented after analysis (SFC) or collected (SFE), or on-line coupled with a second technique, thus providing a multidimensional approach. Off-line methods are slow and susceptible to solute losses and contamination the on-line coupled system makes possible a deaease in the detection limits, with an improvement in quantification, while the use of valves for automation results in faster and more reproducible analyses (16). The off-line... 

The System is built by using three independent modules (SPE, SEE and GC) in Such a way that it can be assembled to perform experiments in the on-line coupled mode (SPE-SEE, SEE-GC, SPE-GC and SPE-SEE-GC) or as independent units (GC, SPE, and SEE). This means that if we want to use the system for standard GC, there will be no problems, with the same applying for both SPE and SEE. 

ON-LINE COUPLING OF SUPERCRITICAL FLUID EXTRACTION WITH CAPILLARY ELECTRODRIVEN SEPARATION TECHNIQUES (SFE-CESTs)... 

M. C. Tavai es and P. M. Lan as, On-line coupling of supercritical fluid extraction with supera itical fluid cltromatogr aphy , 7. Braz. Chem. Soc. in press (2001). 

F. M. Ean as and M. A. Ruggiero, On-line coupling of supercritical fluid exti action to capillaiy column electi odriven separation techniques , J. Microcolumn Sep. 12 61-67 (2000). 

Current interest is, however, mainly in the coupling of HPLC and TLC, to which considerable attention has been devoted for the solution of difficult separation problems. Since Boshoff et al. (39) first described the direct coupling of HPLC and TLC, several papers (40-43) have been published describing the on-line coupling of liquid chromatographic methods and PC, usually with different interfaces, depending on the first technique applied. If PC is used as the second method, all the MD methods discussed above can be applied to increase the separating power. 

S. Palmarsdottir and L. E. Edholm, Enhancement of selectivity and concentration sensitivity in capillary zone electrophoresis by on-line coupling with column liquid chromatography and utilizing a double stacking procedure allowing for microliter injections , 7. Chromatogr. 693 131-143 (1995). 

Multidimensional HPLC offers very high separation power when compared to monodimensional LC analysis. Thus, it can be applied to the analysis of very complex mixtures. Applications of on-line MD-HPLC have been developed, using various techniques such as heart-cut, on-column concentration or trace enrichment applications in which liquid phases on both columns are miscible and compatible are frequently reported, but the on-line coupling of columns with incompatible mobile phases have also been studied. 

In coupled LC-GC, specific components or classes of components of complex mixtures are pre-fractionated by LC and are then transferred on-line to a GC system for analytical separation. Because of the ease of collecting and handling liquids, off-line LC-GC techniques are very popular, but they do present several disadvantages, e.g. the numerous steps involved, long analysis times, possibility of contamination, etc. The on-line coupled LC-GC techniques avoid all of these disadvantages, thus allowing us to solve difficult analytical problems in a fully automated way. 

On-line coupled LC-GC methods have been developed in food analysis for several reasons, i.e. lower detection limits can be reached, the clean-up is more efficient, and large numbers of samples can be analysed with a minimum of manual sample preparation in shorter times. 

F. J. Senorans, J. Tabera and M. Herraiz, Rapid separation of free sterols in edible oils by on-line coupled reversed phase liquid chr omatography-gas chromatography , 7. Agric. Food. Chem. 44 3189-3192 (1996). 

H.-G. Schmarx, A. Mosandl and K. Grob, Stereoisomeric flavour compounds. XXXVIII dkect chir ospecific analysis of y-lactones using on-line coupled EC-GC with a chkal separation column , Chromatographia 29 125-130 (1990). 

G. Pull, G. Ki-ammer and P. Sclneier, On-line coupled HPRC-HRGC A powerful tool for vapoi phase PTIR analysis (RC-GC-PTIR) , 7. High Resolut. Chromatogr. 14 160-163 (1991). 

E. Ibanez, J. Palacios and G. Reglero, Analysis of tocopherols by on-line coupling supercritical fluid extraction-superaitical fluid chromatography , ]. Microcolumn Sep. 11 605-611 (1999). 

Figure 11.3 Typical configuration for the on-line coupling of an achiral and chiral cliro-matograpliic system by means of a switching valve. The non-enantio-resolved solute is isolated on the achiral phase and then stereochemically separated on the chiral phase. Reprinted from G. Subramanian, A Practical Approach to Chiral Separation by Liquid Chromatography, 1994, pp. 357-396, with permission from Wiley-VCH.

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. 

Figure 11.12 GC analysis of (a) urine sample spiked with opiates 3 p.g/ml) and (b) blank urine sample. Peak identification is as follows 1, dihydrocodeine 2, codeine 3, ethylmor-phine 4, moipliine 5, heroin. Reprinted from Journal of Chromatography, A 771, T. Hyotylainen et al., Determination of morphine and its analogues in urine by on-line coupled reversed-phase liquied cliromatography-gas clrromatography with on-line derivatization, pp. 360-365, copyright 1997, with permission from Elsevier Science.

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