Polymeric precolumns

Polymeric precolumns of styrene-divinylbenzene were used by Aguilar et al. to monitor pesticides in river water. Water samples (50 mL) were trace enriched on-line followed by analysis using LC combined with diode-array detection. LC atmospheric pressure chemical ionization (APCI) MS was used for confirmatory purposes. It was found that after the pesticides had been extracted from the water sample, they could be stored on the precartridges for up to 3 months without any detectable degradation. This work illustrates an advantage of SPE for water samples. Many pesticides which may not be stable when stored in water, even at low temperature, may be extracted and/or enriched on SPE media and stored under freezer conditions with no detectable degradation. This provides an excellent way to store samples for later analysis. 

Online trace enrichment is another attractive route for increasing the resolving power of liquid chromatographic methods. An automated system by which nitroxynil in cattle muscle tissue could be loaded onto an anion-exchange precolumn and then eluted and chromatographed on a polymeric analytical column has been described (354). In practice, this is the online and higher performance ana-... 

Precolumn derivatization with a solid-phase derivatizing precolumn has also been reported. Xie et al. (43) applied polymeric permanganate oxidations of alcohols and aldehydes for the production of UV-absorb-ing species. 

The simultaneous HPLC-UV determination of sulfamonomethoxine (SMM), miloxacin (MLX), and OXO in serum and muscle of cultured fish was developed (153). A sample of muscle was extracted with MeCN-THF (95 5) after centrifugation, the supernatant was injected into the HPLC system. A Hisep column, used in this study, is packed with restricted-access materials (RAMs) consisting of the polymeric hydrophilic/hydrophobic phase bound to silica gel. This column did not require time-consuming and complex extraction procedures. The RAM sorbent could also be applied in short precolumns, which are combined directly on-line with the HPLC equipment. This approach is much more convenient than that applied in the present paper. The guard column had to be changed very often in order to protect the analytical column in a sufficient way. The extraction recovery was 79.5%, RSD of 6.0%. 

Polymeric drug delivery system HPLC Precolumn C CH,CN oOmA/PO,. 340 nm Method review [674]... 

ESI and APCI. LC/MS is considerably improved after precolumn oxidation with peroxide to the pentavalent acids (27) and (29). These can be chromatographed on a polymeric PRP-1 column using a standard water-CH3CN-0.2 % formic acid gradient (69). 

Liquid C h rom atography/M ass Spectrometry. Increased use of liquid chromatography/mass spectrometry (lc/ms) for structural identification and trace analysis has become apparent. Thermospray lc/ms has been used to identify by-products in phenyl isocyanate precolumn derivatization reactions (74). Five compounds resulting from the reaction of phenylisocyanate and the reaction medium were identified two from a reaction between phenyl isocyanate and methanol, two from the reaction between phenyl isocyanate and water, and one from the polymerization of phenyl isocyanate. There were also two reports of derivatization to enhance either the response or structural information from thermospray lc/ms for linoleic acid lipoxygenase metabolites (75) and for cortisol (76). 

A sample of povidone or copovidone is analyzed after dissolution in a water/ methanol mixture using HPLC reverse phase chromatography (gradient run). The polymeric material is kept away from the chromatographic system using a precolumn and switching technique. 

Initially, SPE was based on the use of polymeric sorbents, such as XAD resins (polymeric adsorbents), which were packed in small disposable columns for use on drug analysis. The early environmental applications consisted of both XAD resins and bonded-phase sorbents, such as C-18 (McDonald and Bouvier, 1995). These precolumns were used for sample trace enrichment prior to liquid chromatography and were often done on-line, which means at the same time as liquid chromatography. However, these first, steel, on-line precolumns quickly were replaced with an off-line column made of plastic in order to be both inexpensive and disposable. Eventually, the term solid-phase extraction was coined for these low-pressure extraction columns (Zief et al., 1982). Thus, solid-phase extraction is an analogous term to liquid-liquid extraction, and in fact, solid-phase extraction might also be called liquid-solid extraction. However, it is the term solid-phase extraction or the acronym SPE that has become the common name for this procedure. 

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