Optical fiber reflectance sensor coupled to a multisyringe flow injection system for preconcentration and...

A novel optical fiber reflectance sensor is coupled to a multisyringe flow injection system (MSFIA) for the preconcentration and determination of 1-naphthylamine (NPA) in water samples using C18 disks (octadecyl groups). NPA, being a first-class carcinogen, is important from a toxicological point of view and, therefore, its quantification is of considerable interest. In this study, the Griess reaction is used for sensitive and selective spectrophotometric determination of NPA. The reaction involves conversion of nitrite into nitrous acid in acidic medium followed by diazotization of sulphanilic acid and formation of a diazonium salt. The diazonium salt is then combined with NPA to form 4-(sulphophenylazo)-1-naphthylamine, an azo dye. This compound is subsequently retained onto a C18 disk followed by spectrophotometric detection at 540 nm, and it is then eluted with methanol in water (80%, v/v), so that the C18 disk is regenerated for subsequent experiments. Under the established optimum conditions, a calibration graph for NPA was constructed. Good linearity was observed within a concentration range from 10 to 160 microg l(-1). The lineal regression equation is A=(0.0027+/-0.0001) [NPA]+(0.0296+/-0.0047), r=0.9991; relative standard deviation values obtained from the analysis of 10 samples of 10, 80 and 160 microg l(-1) are 4.7, 1.2 and 0.6%, respectively. The mean value relative errors for concentrations of 10, 80, 160 microg l(-1) are 3.4, 0.9 and 0.4%, respectively. The detection and quantification limits were 1.1 and 3.7 microg l(-1). A sampling throughput of 14 injections per hour is achieved. The repeatability calculated for five different C18 disks was E(rel)=2.8%. The proposed technique has been validated by replicate analysis (n=6) of several water samples with spiked NPA, giving satisfactory results.