Optosensing solid phase

In 1985, Ruzicka and Hansen established the principles behind flow injection optosensing [13-15], which has subsequently been used for making reaction-rate measurements [16], pH measurements by means of immobilized indicators [17,18], enzyme assays [19], solid-phase analyte preconcentration by sorbent extraction [20] and even anion determinations by catalysed reduction of a solid phase [21] —all these applications are discussed in Chapters 3 and 4. Incorporation of a gas-diffusion membrane in this type of sensor results in substantially improved sensitivity (through preconcentration) and selectivity (through removal of non-volatile interferents). The first model sensor of this type was developed for the determination of ammonium [13] and later refined by Hansen et al. [22,23] for successful application to clinical samples. 

Integrated systems used both for preconcentration and in situ detection on the column (solid phase optosensing). 

Practical Considerations in the Design of Solid Phase FI Optosensing Systems... 

Techniques and manifolds used for other on-line soiption separation methods described in the previous sections may be used to advantage for solid phase optosensing systems. 

Figure 1 Typical flow-through cells used for spectrophotometric detection in flowing stream methods. (A) U-shaped cell for implementation in standard spectrophotometers (B) Z-shaped cell as commonly employed in liquid chromatography (C) oval-shaped cell used for both liquid-phase measurements and solid-phase optosensing detection (D) solid-state detector with radially transmitted light beam. LS, light source LED, light-emitting diode PD, photodetector.

Alternative 2. By hyphenating an optical fiber sensor for implementing disk-based solid-phase extraction and direct optosensing at the solid surface, there is no need for further elution to perform the optical detection in the eluate phase, as demanded in conventional sorbent-extraction protocols previously reported for sulfide, thus yielding improved enrichment factors [14] (Figure 7.5). 

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