Determination of ultratraces of nitrite by solid-phase preconcentration using a novel flow-through spectrophotometric optrode

A novel sorbent-packed planar wall microcolumn-based optosensor coupled to a flow injection analysis system (FIA) for the determination of traces of n itrite by solid-phase spectrophotometry is presented. The methodology is ba sed on the on-line nitrite derivatization with a modified Griess reagent to form an ate-dye whose retention onto octadecyl-covalently bonded silica ge l by physical adsorption and partitioning is continuously monitored. After the analytical signal has been recorded, the sorbed compound is eluted with 80% methanol/water (v/v), rendering the system ready for the next extracti on. Selection of the solid support and the suitable flow-through cell configura tion are discussed in detail. By minimization of the blank signal, a concen tration of nitrite as low as 1 ng/ml can be easily determined using 2.5 mi of sample. Detection limit (3 sigma (blank)) of 0.46 ng/ml of nitrite, rela tive standard deviation better than 4%, sample throughput of 12 h(-1) and a n enrichment factor of 93 in relation to the conventional spectrophotometri c method were obtained. The utility of the present optosensing system, wherein a mass calibration i s also feasible, was testified by the satisfactory results obtained in its application to tap, rain and aquarium water samples. (C) 2001 Elsevier Scie nce B.V. All rights reserved.