How to Measure Hydrogen Sulfide

Hydrogen sulfide (H2S) is one of the compounds created when wastewater is allowed to stay stagnant in sewer systems; when bacteria metabolize all of the available oxygen in the air, anaerobic bacteria can form and give off hydrogen sulfide as a byproduct. Hydrogen sulfide contains sulfur in its chemical makeup, a substance which is dangerous to the human body and can even be fatal at high levels. A gas chromatograph can measure H2S levels by separating and measuring the individual compounds of a gas sample.

Things You'll Need

• Syringe
• Acetone
• Paper towels
• Gas sample
• Gas chromatograph
• Online/print chemical database
• Partner
• Pencil

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Instructions

• 1

  Draw acetone into the syringe until full to clean it. Dispose of the acetone by expelling it onto paper towels and then throw the paper towels away. Let the acetone air dry from your syringe for at least a half an hour.

• 2

  Depress the plunger on the syringe to expel all of the air. Insert the syringe needle into the gas sample containing hydrogen sulfide. Draw the gas sample into the syringe by pulling up the plunger until the sample fills the syringe.

• 3

  Find the boiling points of any other chemical substances included in the sample along with the hydrogen sulfide. This information is often included in chemical databases, which can be found either online or in print form.

  When the gas chromatograph prints its report onto the chart paper, different compounds will reach the detector at different times resulting in multiple peak areas, each peak area proportional to the amount of the compound in the sample. A peak area is created any time the pen arcs upward, which indicates that the chromatograph is detecting a new compound. Higher boiling points will take longer to reach the chromatograph's detector; if H2S has the second-highest boiling point of four compounds, it will be represented by the third peak area. The boiling point of hydrogen sulfide is 60.7 degrees Celsius.

• 4

  Turn on the gas chromatograph. Adjust the settings for chart speed and baseline if necessary. Make sure that the chromatograph's pen is placed firmly against the chart paper and that the chart paper is taut.

• 5

  Insert the filled syringe into one of the sample intakes on the gas chromatograph. Depress the plunger to expel the entire sample into the gas chromatograph. Have a partner make a marking on the chart paper in pencil on the baseline at the moment that the sample is inserted into the chromatograph.

• 6

  Find the area of the peak area on the chart paper representing the amount of H2S in the sample. The area of an arc can be found by multiplying its height by the arc's width at half its height.

• 7

  Find the total area of all peak areas representing compounds found in the gas sample which you put into the chromatograph. Divide the area of the peak area by the total area of all peak areas found on the chromatograph's chart paper. Multiply the result by 100 to find the percentage of hydrogen sulfide within the sample.