Sniffing out an ill wind
Chemiluminescence detects low levels of sulfur in the air.
Lynn M. Savage
Volatile sulfur compounds are found in polluted waters and garbage heaps and are the major component of halitosis — your own bad breath. Two of these compounds — dimethyl sulfide (DMS) and methyl mercaptan, also known as methanethiol (CH3SH) — have strong and unpleasant odors that quickly summon mental images of the sewers and toilets with which they are most closely associated.
A custom chemiluminescence cell helps distinguish volatile sulfur compounds, collecting dimethyl sulfide and methyl mercaptan from the air, trapping and separating them within a single column, and detecting their presence with parts-per-billion resolution. Adapted from Analytical Chemistry with permission from the American Chemical Society.
Some researchers believe that the ability to analyze the sulfur compounds in one’s breath could aid clinical diagnosis of such conditions as liver failure and transplant rejection. Such analysis also could help address the toxic and oftentimes corrosive effects of some of the compounds, which, though not very acidic naturally, can become so when broken down into SO2 by the atmosphere. However, it is difficult to collect, store and analyze volatile sulfur compounds because they are highly adsorptive and reactive.
Now Kei Toda and his colleagues at Kumamoto University in Japan have devised a detection method for volatile sulfur compounds that collects CH3SH and DMS from the air, traps and separates them within a single column and detects their presence with parts-per-billion resolution.
The researchers built a reaction cell in which they could induce chemiluminescence from the separated sulfur compounds via an interaction with piped-in ozone. They captured light from the O3-induced reactions with a photomultiplier tube from Hamamatsu Photonics KK of Japan.
They first used the instrument to analyze human breath and the headspace inside a septic tank. Moreover, because the device measured only 40 × 30 × 35 cm, they also used it to test the air quality in a toilet room. Concurrently, they used gas chromatography with a flame photometric detector (GC-FPD) — the conventional technique for detecting sulfur compounds — to compare with the new method.
They found that, although the data obtained by both methods were mostly in good agreement, the chemiluminescence technique took less time to trap and measure the analytes and could measure CH3SH at lower concentrations than the conventional method, probably because the latter permits the volatile compounds to react with other substances prior to detection.
Furthermore, their technique could detect both CH3SH and DMS in some cases where the GC-FPD system could not, such as when testing the breath of test subjects who were smokers.
The researchers’ experiments in the toilet room were conducted semicontinuously over three days, with more than 200 measurements recorded during that span using the same equipment throughout. They found that CH3SH was present in parts-per-billion levels, and DMS at even lower levels, each spiking shortly after nightfall each day, but overall at less abundance than expected.
According to Toda, the compact instrument can be used anywhere that AC power is available. However, if a smaller photomultiplier tube with the same sensitivity were available, that would help hold down cost, size and handling.
“We are planning to develop a portable total-sulfur gas measurement system [that will detect] hydrogen sulfide, carbon disulfide, carbonyl sulfide and dimethyl disulfide [as well as CH3SH],” he said.
Analytical Chemistry, Sept. 1, 2006, pp. 6252-6259.
- A chemical reaction involving the production of light. The reaction of ethylene with ozone is chemiluminescent.
MORE FROM PHOTONICS MEDIA