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Issue 10, 2001
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A novel flow-through disk-based

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A novel, versatile and sensitive flow-through optical fiber diffuse reflectance sensor to implement disk-based solid-phase extraction in a flow injection analysis (FIA) system is presented. Nitrite optosensing at trace levels is chosen as a model of chemistry to demonstrate its applicability. The methodology is based on on-line nitrite derivatization with Shinn reagent to form a moderately polar azo dye, whose preconcentration on to octadecyl covalently bonded silica gel particles tightly bound to an inert matrix (C18 disk) is continuously monitored using a plug-in diode-array spectrophotometer. After the analytical signal has been recorded, fast sensor regeneration is achieved with a methanolic eluent, rendering the system ready for the next extraction. Selection of the solid disk support and the suitable flow-through cell configuration to reduce back-pressure effects are discussed in detail. By matching the illumination and retention zones, concentrations of nitrite as low as 1 ng ml−1 are easily determined using 2.5 ml of sample. A detection limit (3σblank) of 0.1 ng ml−1 of nitrite, repeatability and reproducibility better than 3.2%, an analytical throughput of 11 h−1 and an enrichment factor of 140 are the figures of merit of the proposed optrode. The utility of the flow-through optosensing system, wherein minimization of additive matrix interferences is feasible, was testified by the satisfactory results obtained in its application to tap, ground, harbor and aquarium water samples.

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Article information

23 May 2001
11 Jul 2001
First published
19 Sep 2001

Analyst, 2001,126, 1740-1746
Article type

A novel flow-through disk-based solid-phase extraction diffuse reflectance optrode. Application to preconcentration and determination of trace levels of nitrite

M. Miró, W. Frenzel, J. M. Estela and V. Cerdà, Analyst, 2001, 126, 1740
DOI: 10.1039/B104553A

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