Enrichment, aqueous samples

J. J. Vreuls, R. T. Gliijsen, G. J. de Jong and U. A. Th Brinkman, Drying step for introduction of water-free desorption solvent into a gas cliromatograph after on-line liquid clir omatograpliic Cace enrichment of aqueous samples , 7. Chromatogr. 625 237 - 245 (1992). 

H. G. J. Mol, H.-G. Janssen, C. A. Cramers and U. A. Th Brinkman, On-line sample enrichment-capillary gas clir omatography of aqueous samples using geometr ically deformed open-tubular extraction columns , 7. Microcolumn Sep. 7 247-257 (1995). 

Figure 5.3 Analysis of 100 ml of (a) surface water and (b) drinking water sample spiked with 0.1 pig/ml of microcystins, using column-switching HPLC 1, microcystin-RR 2, microcystin-YR 3, microcystin-LR. Reprinted from Journal of Chromatography A, 848, H. S. Lee et al, On-line trace enrichment for the simultaneous determination of microcystins in aqueous samples using high performance liquid chromatography with diode-array detection , pp 179-184, copyright 1999, with permission from Elsevier Science.

W. Golkiewicz, C. E. Werkhoven-Goewie, U. A. Th Brinkman, R. W. Erei, H. Colin and G. Guiochon, Use of pyrocarbon sorbents for rtace enrichment of polar compounds from aqueous samples with on-line HPEC analysis , /. Chromatogr. Sci. 21 27-33 (1981). 

E. R. Brouwer, H. Lingeman and U. A. Th Brinkman, Use of membrane extr action disks for on-line trace enrichment of organic compounds from aqueous samples , Chromatographia 29 415-418 (1990). 

Noroozian E, Maris FA, Nielen MWF, et al. 1987. Liquid chromatographic trace enrichment with on-line capillary gas chromatography for the determination of organic pollutants in aqueous samples. Journal of High Resolution Chromatography and Chromatography Communications 10 17-24. 

Future efforts in the field of environmental analysis will be focused on several fronts, including analyte enrichment and measurement, on-line and on-site techniques, multi-residue methodology, direct injection of aqueous samples into LC/MS/MS... 

Hennion MC, Coquart V. 1993. Comparison of reverse-phase extraction sorbents for the on-line trace enrichment of polar organic compounds in environmental aqueous samples. J Chromatogr 642 211-224... 

Liquid extraction FOR THE SEPARATION and enrichment of organic compounds in aqueous samples has been used successfully. Automated solvent extraction with flow-injection analysis has been reported (I). 

WA Minnaard, J Slobodnik, JJ Vreuls, KP Hupe, UAT Brinkman. Rapid liquid-chromatographic screening of organic micropollutants in aqueous samples using a single short column for trace enrichment and separation. J Chromatogr A 696 333-340, 1995. 

Water exhibits very strong absorption bands in the mid-IR region, which generally precludes its use as a solvent for IR spectroscopy. Aqueous samples can be analyzed by so-called ATR-spectroscopy (Fahrenfort, 1961 Harrick, 1979), see Sec. 6.4. However, ATR detection limits are often too large. Therefore further effort is necessary to exclude water and to enrich the organic compound in the area where the evanescent wave is penetrating the sample. 

Therefore, altering cIm effects the time constant less than expected without the Nernst diffusion layer. The time con.stants r for the enrichment from aqueous samples in a PDMS membrane are of the order of 10 to 600 s for small molecules like benzene derivatives and up to e.g. 3600 s for 2-chlorobiphenyl (Table 6.5-4). 

For instance, the large solubility of dichloromethane in water causes a relatively low enrichment factor of ca. 80 (PDMS, 30 °C). As a result the detection limit for direct measurements of aqueous solutions with membrane covered IRE s is ca. 1.9 -10 mol/L. Using the head space variant with heated aqueous sample (90 °C) and cooled IRE (5 °C) the detection limit is improved by a factor of 30 to 6.2 10 mol/L. 

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