Post-column detection configuration

In the post-column detection configuration, detection is carried out at a location remote to the outlet of the capillary. For example, in radionuclide detection, the capillary eluent is spotted onto a membrane or collected as fractions, and subsequently exposed to a scintillator for detection Postcolumn detection allows for the separation and detection to be independently optimized. In the case of radionuclide detection, the detector integration time can be maximized without a corresponding loss in resolution (see Section 9.2.2). 

Immobilized /3-glucosidase served for enzymatically catalyzed hydrolysis of benzene metabolites in urine. End analysis of phenol was by RP-HPLC with ELD at 0.85 V vi. Ag/AgCl electrode. ELD avoids interference from other componnds present in urine. LOD was 10 p.gL" (20 p,L injection, 0.2 ng), with RSD 1.16% and 3.38% for 1.2 ng and 2.0 ng, respectively. A stndy was carried out of two FIA systems for enzymatically catalyzed determination of dopamine (10a). Thus, a combination of a packed bed reactor containing immobilized tyrosinase followed by photometric detection was compared with ELD based on a graphite electrode with its surface covered by immobilized tyrosinase. The former configuration was linear up to 0.75 mM while the latter reached 1 mM. LC separation and post-column detection with the bioelectrode was applied to analysis of spiked serum samples. ... 

Both on-column and post-column detection schemes have been developed for radionuclide detection for CE. The most common type used is an on-column configuration, which yields detection limits in the 10 M range for isotopes such as P. Isotachophoretic separations of C were among the first examples of online capillary radionuclide detection, performed by Kaniansky et al. The associated instmment uses 300-p,m ID fluorinated ethylene-propylene copolymer capillary tubing, and the separation eluent flows directly into a plastic scintillator cell between two PMTs. The scintillation events are detected coincidentally between the two PMTs, such that only if both PMTs receive an input within a short time will they register the count as signal. This kind of coincidence detection ensures that nonscintillation photons that come from outside the detection cell and only hit one PMT are not counted. This system exhibits a detection limit of 16 Bq for analytes, with a detector efficiency of 13-15%. 

For a direct transponation. the shonest and thinnest conduits that are practical should be used in order to avoid unnecessary dispersion. The dispersion contribution of various transport conduits in FI-AAS systems have been studied in detail, and the importance of tube diameter, length and configuration have been stressed [5]. The dispersion contribution of this seemingly unimportant system component may often be overlooked. However, to obtain optimum performance, careful minimization of dispersion is required, especially when the columns are small, and the concentrate zones in the eluate well-focused. A shortest possible length, not exceeding 20 cm of 0.35 mm i.d tubing has been recommended for the transport conduits in AAS applications, and should be also applicable to other detection systems which do not require post column reactions. 

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