Fish. Oceans Canada: UV Sulfide: Total free sulfides in marine sediments using UV spectrophotometry
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Official Method Name
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A simple and rapid method for measuring total free sulfides in marine sediments |
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Current Revision
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Media
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Porewater |
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Instrumentation
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Ultraviolet spectrophotometry |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Brief Method Summary
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A Rhizon tube is inserted into sediment cores or grab samples with undisturbed sediment-water interfaces. The tube is flushed by pulling and then discarding 0.5 – 1 mL of porewater. A 100-uL porewater sample is immediately removed from inside the Rhizon tube by inserting the needle attached to a 100-uL gas-tight syringe. The 100-uL porewater sample is immediately added to a 1.4-mL capacity semi-micro quartz cuvette (1-cm path length) along with 1 mL of deionized water having a pH of ~8 (adjusted with 0.44 mol/L ammonium hydroxide and confirmed using pH-indicator test strips). Immediately after sample preparation, light absorption by HS- is determined at 230, 240, or 250 nm wavelengths by UV spectrophotometry. The instrument is blanked with the alkaline dilution water before adding the porewater sample. Five working standards ranging from 100 to 15,000 umol/L are prepared by diluting the concentrated stock volumetrically with deionized distilled water. One hundred microliter volumes of each standard are added to 1 mL of the buffered water in the cuvette and the absorption spectra are obtained. |
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Scope and Application
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This method covers the determination of total free sulfides in porewater of marine sediments |
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Applicable Concentration Range
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200 - 15,000 umol/L |
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Interferences
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(A) Bromine, nitrate, and nitrite have absorbance spectra that overlap with that of HS-. The absorption spectra of Br- and NO2,3- are sufficiently resolved from that of HS- and/or are not present at high enough concentration to affect S2- measurement accuracy. (B) DOC absorbance can bias the absorbance baseline at 230 nm. This only affects HS- concentrations near zero. (C) Iodide absorption spectra greatly overlap that of S2-. Set LOQ at 200 umol/L. |
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Quality Control Requirements
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Blanks (alkaline dilution water), Working standards (100–15,000 umol/l). |
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Sample Handling
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Analyze immediately to avoid oxidation and gaseous loss of sulfide from the samples. |
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Maximum Holding Time
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Analyze immediately |
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Relative Cost
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Sample Preparation Methods
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