Ion-pair SPE

Blood, stomach content, tissues Miscellaneous compounds Group tests, specific tests, particular methods Ion-exchange columns, formation of ion-pairs, SPE, LLE, continuous extraction GC-MS LC-MS... 

Alternatively, ionic compounds can be recovered from solution on hydrophobic sorbents using ion-pair SPE (IP-SPE). Carson [121] notes that advantages of IP-SPE over ion-suppression RP-SPE or ion-exchange SPE include selectivity, compatibility with aqueous samples and rapid evaporative concentration of eluents, and potential application to multiclass multiresidue analysis. IP reagents (e.g., 1-dodecanesulfonic acid for pairing with basic analytes or tetrabutylammonium hydrogen sulfate for pairing with... 

Pocurall et al. [76] applied on-line ion-pair SPE of oidy 15 ml water on a PLRP-S cartridge and ion-pair LC using triethylamine as ion-pairing agent in the LC-MS analysis of naphthalene monosulfonates in tap water, seawater, and river water, providing detection limits of 0.05-1 pgd in SIM on ions corresponding to the loss of SO2 and the formation of the SOj radical ion. 

Gimeno, R. A., Beltran, J. L., Marce, R. M., and Bormll, F., Determination of naphthalenesulfonates in water by online ion-pair SPE and ion-pair liquid chromatography with fast-scanning fluorescence detection, J. Chromatogr. A, 890, 289-294, 2000. 

Castro, R., Moyano, E., and Galceran, M. T., Online ion-pair SPE-liquid chromatography-mass spectrometry for the analysis of quaternary ammonium herbicides, J. Chromatogr. A, 869, 441-449,... 

Ion pair-SPE with MlPs (moleculary imprinted polymers)... 

An alternative way of eliminating water in the RPLC eluent is to introduce an SPE trapping column after the LC column (88, 99). After a post-column addition of water (to prevent breakthrough of the less retained compounds), the fraction that elutes from the RPLC column is trapped on to a short-column which is usually packed with polymeric sorbent. This system can use mobile phases containing salts, buffers or ion-pair reagents which can not be introduced directly into the GC unit. This system has been successfully applied, for example, to the analysis of polycyclic aromatic hydrocarbons (PAHs) in water samples (99). 

To determine secondary alkanesulfonates in sewage wastewaters, solid phase extraction (SPE) and a single-step procedure which combines elution and injection port derivatization for analysis with GC-MS were developed [36]. Again a tetrabutylammonium ion pair reagent was employed both to elute the secondary alkanesulfonates as their ion pairs from CI8-bonded silica disks and to derivatize sulfonate ion pairs under GC injection port conditions. Secondary alkanesulfonates were effectively recovered from samples of raw sewage (>92%) and from primary (>98%) and secondary (>85%) effluents. No... 

All these methods give similar results but their sensitivities and resolutions are different. For example, UV-Vis spectrophotometry gives good results if a single colorant or mixture of colorants (with different absorption spectra) were previously separated by SPE, ion pair formation, and a good previous extraction. Due to their added-value capability, HPLC and CE became the ideal techniques for the analysis of multicomponent mixtures of natural and synthetic colorants found in drinks. To make correct evaluations in complex dye mixtures, a chemometric multicomponent analysis (PLS, nonlinear regression) is necessary to discriminate colorant contributions from other food constituents (sugars, phenolics, etc.). 

As expected, LC separation of the dichloromethane/acetone SPE eluate in the RP-mode, presented as FIA-APCI-MS(+) in Fig. 2.12.13, was impossible because the alkyl ethoxy amines as cationic surfactants could not be eluted under conventional RP-separation conditions [37, 53]. The use of methane sulfonic acid for ion-pairing resulted in the separation of the compounds in the methanol eluate as shown as TIC (d) and selected ion trace masses (m/z 504 (a), 670 (b), and 802 (c)) in Fig. 2.12.14. Here, the short-chain ethoxy amines were eluted later than the more polar long-chain homologues [39]. 

There is a recent trend towards simultaneous CE separations of several classes of food additives. This has so far been applied to soft drinks and preserved fruits, but could also be used for other food products. An MEKC method was published (Lin et al., 2000) for simultaneous separation of intense sweeteners (dulcin, aspartame, saccharin and acesulfame K) and some preservatives (sorbic and benzoic acids, sodium dehydroacetate, methyl-, ethyl-, propyl- and isopropyl- p-hydroxybenzoates) in preserved fruits. Ion pair extraction and SPE cleanup were used prior to CE analysis. The average recovery of these various additives was 90% with good within-laboratory reproducibility of results. Another procedure was described by Frazier et al. (2000b) for separation of intense sweeteners, preservatives and colours as well as caffeine and caramel in soft drinks. Using the MEKC mode, separation was obtained in 15 min. The aqueous phase was 20 mM carbonate buffer at pH 9.5 and the micellar phase was 62 mM sodium dodecyl sulphate. A diode array detector was used for quantification in the range 190-600 nm, and limits of quantification of 0.01 mg/1 per analyte were reported. The authors observed that their procedure requires further validation for quantitative analysis. 

A combination of chomatographic techniques such as CZE-UV, ion-pair LC-DAD and ion-pair LC-electrospray mass spectrometry was employed for the separation of polar hydrophilic aromatic sulphonates. SPE preconcentration of aromatic sulphonates was studied in detail. Sorbents LiChrolut EN, Isolute ENV+, HR-P and Oasis HLB were included in the experiments. They were activated by rinsing 7 ml of methanol followed with 3 ml of water acidified to pH 2.5 with sulphuric acid. Water samples were passed... 

Aboul-Enein and Al-Duraibi (1998) employed dansyl chloride in a fluorescence assay for PUT, SP, SPD, and their acetylated derivatives by ion-pair reverse-phase chromatography. This assay could be applied to the separation of free and acetylated polyamines in biological samples. Dansyl chloride has also been used as the fluorescence reagent in the determination of polyamines in urine by Molins-Legua and colleagues (1999). Derivatization was carried out within the C18 cartridges that were used during the SPE extraction procedure. Recoveries were 80-95% for all four polyamines analyzed and the hmit of detection was 10 ng/ml. 

C4-C6) compounds. For longer chains, less polar or non-polar SPE phases (C18 and Oasis HLB) may be applied. When an ion-pairing agent is used, that decreases the polarity of the ion-pair complex, a non-polar solvent (MTBE) may be used. Non-ionic PFASs may be extracted from the matrix by non-polar media (Cl8 SPE or hexane). Moderate polar media (Oasis HLB and Oasis WAX-SPE, a hexane-acetone mixture or acetonitrile) have also been applied for extraction of non-ionic PFASs. 

CHCLs/EtOAc extn, SPE cleanup, liq-liq partn, ion-pair extn... 

Ion pair/ACN extn, basic alumina addn, liq-liq partns, tandem SPE cleanup... 

The same derivatization was applied to the HPLC determination of STR and DHS in milk. The comparison of HPLC and ELISA methods was also performed for DIHS. After removal of fat by extracting a milk sample with oxalic acid and centrifuging, proteins were precipitated with TCA. The supernatant was treated by SPE on a Cl8 column. The cartridge was washed with water, and the analytes were eluted with ion-pair in MeCN. The eluate was reconcentrated by evaporating and dissolving in water. Postcolumn reaction took place at 65°C. Recoveries were dependent on the concentration level and the batch of SPE columns used, and independent of the fat content and homogenization. The sample cleanup was not sufficient for the analysis of cheese. The DIHS concentrations of incurred samples determined by ELISA were higher than those obtained by the LC method (107). 

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