Cation-exchanger packed precolumn

Figure 4. Standards recovered from 10 mL of distilled-deionized water on a strong-cation-exchanger packed precolumn. Peak identities 4, 0.14 pg of caffeine 5,0.20 pg of pentachlorophenol 6y 0.42 pg of aniline 7,0.061 pg of m-nitroaniline 8, 0.15 pg of atrazine 9, 0.40 pg of quinoline 10, 0.26 pg of 2,6-dichloroaniline 11,0.14 pg of N-nitrosodiphenylamine and 12,0.055 pg of pyrene. Conditions for concentration, analytical separation, mobile-phase gradient, and detection were the same as in Figure 3. Reproduced with permission from reference 18.)...

For avoiding these manual and time-consuming extraction methods, the use of packed precolumns coupled to reversed-phase (RP)-HPLC equipped with a conventional six-port injector is a suitable alternative, especially for small sample volumes. Techniques for online sample preparation combined with two-dimensional (2-D) HPLC allow PG extraction on a strong cation exchange material directly transferable onto RP-separation columns as recently described for the analysis of cell culture supernatants with tandem MS (MS/MS) detection." ... 

In the second method, there was no prepurification Dopa was measured directly. The separation of Dopa and tyrosine was carried out on a cationic ion-exchange HPLC (sulfonated fluorocarbon polymer) protected with a precolumn packed with silica pellets. The column was eluted with a mobile phase of 10 mM acetate buffer (pH 3.70) with 1% (v/v) propanol. The separation of tyrosine and Dopa is shown in Figure 9.1A. Because of its unique natural fluorescence, the Dopa can be monitored with a fluorescence detector without interference from endogenous substances. An excitation wavelength of 281 nm was used with the emission of 314 nm. 

Bonded-phase silica materials are the most widely used particles for SPE. Since the technology of bonded-phase silica packings for LC columns was already well developed, it was relatively easy for suppliers to offer similar materials in a form suitable for SPE. The most common types are listed in Table 1. Octadecylsilane, or sometimes octylsilane, particles are used for retention of relatively hydro-phobic organic analytes from predominately aqueous samples. A more polar particle, such as cyano-propylsilane, is selected for SPE of less hydrophobic analytes. Cation- and anion-exchange resins are used in small precolumns to concentrate sample ions from very dilute aqueous samples prior to their... 

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