Development and application of a shipboard method for spectrophotometric determination of nanomolar dissolved sulfide in estuarine surface waters using reverse flow injection analysis coupled with a long path length liquid waveguide capillary cell

Abstract

An automated and sensitive colorimetric method was established for on-line determination of trace sulfide concentrations in estuarine surface waters using reverse flow injection analysis coupled with a liquid waveguide capillary cell (LWCC). The mixed reagent was injected into the sample stream, with detection performed using a 1 m path length LWCC with a detection wavelength of 665 nm. Experimental parameters were optimized using an orthogonal and univariate experimental design. Interference from co-occurring ions such as NO2−, NO3−, SO32−, S2O32−, and HCO3− was also investigated. The proposed method exhibited high sensitivity with a detection limit of 1.7 nmol L−1. Linearity was achieved within the range of 10–1200 nmol L−1, with the upper limit extended to 32 μmol L−1 by replacing the LWCC with a 3 cm flow cell. The recovery rates ranged between 96.2% and 106%, with a relative standard deviation (RSD) of 2.01% (n = 14) for samples spiked with 100 nmol L−1 sulfide standard. The proposed method exhibits various advantages, including no effect from salinity or carry-over, a wide linear range (10–1200 nmol L−1 with LWCC and 0.25–32 μmol L−1 with a 3 cm flow cell), low detection limit (1.7 nmol L−1), low reagent consumption (0.095 mg N, N-dimethyl-p-phenylenediamine dihydrochloride and 0.063 g Fe(NH4)(SO4)2 per sample), and high sample throughput rates (24 h−1). This method was successfully applied in a shipboard environment for the analysis of dissolved sulfide in surface waters of the Jiulong Estuary (China).