Flow-injection spectrofluorimetric determination of sulphate using calcein and zirconium

Sulphate can be determined spectrofluorimetrically (λem = 505 nm, λex = 410 nm) based on the formation of a ternary complex between sulphate, zirconium and calcein in a flow-injection system. The carrier stream was deionised water and the reagent streams were 100 μg ml−1 Zr (as ZrOCl2) in 1% (v/v) hydrochloric acid, and 40 μg ml−1 calcein in 0.1 M potassium hydroxide. The injection rate was 50 h−1. The calibration graph was linear up to 25 μg ml−1 SO2−4 based on 250-μl injection volumes. The relative standard deviation (n = 10) was 1.95% for 10 μg ml−1 SO2−4; the detection limit was 0.82 μg ml−1 SO2−4. The system has been applied to the determination of sulphur in NIST coal samples after oxygen bomb combustion.