Automated Determination of Sulfide as Hydrogen Sulfide in Waste Streams By Gas-phase Molecular Absorption Spectrometry

Abstract

The gas-phase molecular absorption spectrometric method for determining sulfide was applied to the determination of sulfide in waste water using a fully automated system. The instrumentation utilizes a commercially available vapour generator and an absorption cell placed in the optical path of an atomic absorption spectrometer set at 200 nm. A sulfide anti oxidant buffer (SAOB) consisting of sodium hydroxide (0.5 mol l ^{- 1} ), sodium tetrahydroborate (0.2 mol l ^{- 1} ) and sodium citrate (0.2 mol l ^{- 1} ) was found to have advantages in terms of shelf-life over existing SAOB formulations. A gas–liquid separator was designed that also assisted in the transport of the hydrogen sulfide, generated by hydrochloric acid (0.6 mol l ^{- 1} ), to the absorption cell. The limit of detection was 0.13 mg l ^{- 1} of sulfide and the calibration was linear up to 100 mg l ^{- 1} . Of 16 ions tested for interference, at a 50-fold excess, only copper, lead, zinc and arsenic gave serious interference problems. The method was applied to the determination of sulfide in waste waters and good agreement was found with the stabilized iodine titration procedure. Spike recoveries from the waste water ranged between 97 and 101%. Unattended operation allowed the analysis of up to 90 samples per hour.