Magnetic solid-phase extraction and a portable photocolourimeter using a multi-colour light emitting diode for on-site determination of nitrite

In this study, a new, simple, cheap, fast method for on-site determination of trace amount of nitrite in atmospheric liquids and surface water is suggested. The proposed method is based on a combination of magnetic solid phase extraction with a designed portable photometer based on light-emitting diodes. The colour reaction of nitrite was carried out with 4-nitroaniline in acidic medium and then coupled with naphth-1-ol in alkaline medium to form an azo product. The reaction and extraction conditions (e.g., acidity for diazotization and alkalinity for naphth-1-ol coupling, and other reagent concentrations, amount of sorbent, desorption solvent type and volume, etc.) were optimized. Under the optimal conditions, the calibration graph was linear in the range of 0.01-0.3 mg L-1 with the limit of detection (LOD) of 0.0013 mg L-1. The enhancement factor was about 110. Relative standard deviations (RSDs) for the extraction of 0.03 and 0.1 mg L-1 of nitrite were obtained 2.49% and 5.34% for five replicates, respectively. The proposed method was able to analyse nitrite ion in water samples with satisfactory recovery ranged from 87% to 103%.