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

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 mu mol 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 mu mol 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).

Automated summary

An automated and sensitive colorimetric method was developed for online determination of trace sulfide concentrations in estuarine surface waters. The method showed high sensitivity, wide linear range, low detection limit, low reagent consumption, and high sample throughput rates, making it advantageous for practical applications.