Total Sulfides Determination

Sulfides, formed by the bacterial reduction of sulfates in rocks and ores, are usually found in groundwater, especially in hot springs. Sulfides in water and wastewater can be divided into three categories. Total sulfides including dissolved sulfides as well as acid-soluble metal sulfides in suspension. Gaseous hydrogen sulfide has an unpleasant odor, and is highly toxic to humans, therefore can be used as a chemical asphyxiant. Dissolved sulfide is toxic to fish and other aquatic organisms. Sulfides also react with metals to form metal sulfides. Biological oxidation of sulfides may form highly corrosive sulfuric acid and can erode concrete sewer pipes. Sulfide can be measured as either total sulfide or dissolved sulfide. Dissolved sulfides include H₂S and HS^- species; total sulfides include dissolved sulfide species, as well as any acidic volatile metal sulfides present in the particulate matter. Due to the degree of complexity associated with measuring dissolved sulfides, total sulfide (as H₂S) is often used as a screening measure to determine if contamination is present in the water body of the environment. BOC Sciences This method is applicable to the quantitative determination of sulfide in water.

In order to deliver the high-precision and small-error determination results, BOC Sciences has developed a colorimetric and UV-based detection technique to detect total sulfides in wastewater.

Figure 1. Overview of environmental sources and fate of hydrogen sulfide. (Michael, T.; et al. 2017)

Application of Our Services

• Determination of total sulfide, dissolved sulfide and hydrogen sulfide in industrial water and industrial wastewater
• Analysis of industrial wastewater containing sulfide ions at concentrations of 0.1 to 20 ppm
• For water analysis containing larger concentrations of sulfide ions, we can analyze water containing more than 20 ppm of sulfide ions by dilution operation

Figure 2. Sulfide solubility chart showing the relative fraction of each sulfide species at different pH. (Marianne, H.; Harald, H. S.2014)

Wet Chemical Analysis Methods

Methylene Blue Colorimetric Method

A broad range of colorimetric methods have been developed for the measurement of various sulfides by employing methylene blue. At BOC Sciences, we apply the methylene blue method which is based on the reaction of sulfide, a mild oxidizer, potassium dichromate and dimethylphenylenediamine to produce methylene blue.

• Sample collection

We collect water samples in 250mL plastic bottles and soil/solids samples in 250mL plastic bottles.

• Sample preservation

Zinc sulfide (in the form of H₂S and HS^-) in water is preserved using zinc acetate and sodium hydroxide to cause precipitation of zinc sulfide, resulting in stabilization

• Sample handling

After the reaction of zinc sulfide with N,N-dimethyl-p-phenylenediamine and ferric chloride under acidic conditions, the zinc sulfide precipitate in the sample is measured by colorimetric method

• For complex matrix samples or samples with high chromaticity, we use matrix isolation techniques to prevent interference due to sample color or chemical matrix effects
• Matrix isolation techniques supported by BOC Sciences include membrane dialysis, distillation or manual sample pretreatment

• Sulfide Detection

BOC Sciences has introduced the advanced inductively coupled plasma atomic emission spectrometry (ICP-AES) technology to measure sulfur in natural water samples, and the emission intensity is mainly from sulfate

Direct Ultraviolet Spectrophotometric Determination

BOC Sciences supports the use of gas chromatography-based methods for determining ultra trace concentrations of total sulfides. We can determine total sulfide concentrations by using direct UV spectrophotometric detection of disulfide ions in samples. This method is simple and fast.