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RESEARCH PROFILES Now available: chemiluminescent analyzer for arsenic in water
JASON V. DYKE AND PURNENDU K. DASGUPTA
Although the cryotrap was eliminated, quantitatively distinguish As(III) from Wading through the scientific literature the method was still cumbersome and As(V). The oxidation state of the ardoes eventually pay off. In the October had poor detection limits. Dasgupta says senic is critical information. Some water 15 issue of Analytical Chemistry (pp that if the literature is to be believed, treatments only work with As(V) and 7088–7097), Purnendu “Sandy” Dasthe reaction just wasn’t practical for not with As(III). As(III) is regarded by gupta and colleagues at Texas Tech most researchers as the more University and the U.S. Geotoxic species, although some logical Survey bring back a debate exists. chemiluminescent reaction, last The investigators showed described in the literature more that NaBH4 reduced the two than a decade ago, to quantify two inorganic species of arsenic, arsenic species to different exAs(III) and As(V), in water. The tents at different pHs. At pH measurement is completed in 4– ≤1, both species are reduced to 6 min in an automated instruarsine, but at pH 4 –5, only ment with only 3 mL of water. As(III) is reduced. In 6 min, it The disastrous effects of was possible to sequentially arsenic in drinking water in carry out the reduction first at countries such as Bangladesh, pH 4 –5 and then at pH ≤1 to India, and China have been quantitate both arsenic species. well documented. Victims sufThe detection limits were 0.05 fer from various illnesses, inµg/L for As(V) and As(III) at Ademola D. Idowu, one of the authors of the paper, helped to decluding skin, bladder, and lung pH ≤1 and 0.09 µg/L for velop a chemiluminescent analyzer that could be used in Banglacancers and disorders of the re- desh and other countries to quantify arsenic in drinking water. As(III) at pH 4–5. productive, neurological, and NaBH4 is an expensive immunological systems. Several analytifield measurements of arsenic in water. reagent and unstable over long periods cal methods have been applied to the But fortunately, he adds, when he and of time. Dasgupta and colleagues formeasurement of arsenic in drinking his colleagues did a recent literature mulated a 4% NaBH4 solution in 0.5 M water, but each method has its own search, “I didn’t read most of the paNaOH, 1 mM Na2EDTA that was stalimitations, especially in the field. pers thoroughly!” ble for at least a month and less expenDasgupta says he first heard of the The reaction struck the investigasive than the high-grade version. chemiluminescent reaction between artors’ fancy because they had previously The next step will be to get the insine (AsH3) and ozone in the 1980s. worked with solution- and gas-phase strument out of the research lab. The However, the implementation of the re- chemiluminescence (Anal. Chem. 2003, analyzer has the features of a field instru75, 5916–5925). “We thought that soment: it’s the size of a large briefcase, action at the time wasn’t feasible for a lution-handling technology had imonly costs ~$2,300 (not counting a field test. Researchers needed to take proved so much that we could take adcomputer) to build, and can be used for ~20 mL of water, purge it with helium thousands of analyses. “You can have it to get rid of air, and add acid and boro- vantage of that to look at the reaction,” explains Dasgupta. as a sophisticated setup as a process meahydride to generate arsine. Water vapor The investigators converted As(III) surement application here in the U.S. or had to be removed from the arsine gas. and As(V) into arsine by reacting the in- in the field in Murshidabad [India] or The gas was captured in a cryotrap organic species with sodium borohyBangladesh,” says Dasgupta. cooled by liquid nitrogen; the cryotrap dride (NaBH4) under controlled pH To make the instrument accessible to was then warmed up to release the gas those who need it, “We have taken the as a plug. Ozone had to be generated conditions. Once the arsine was generfrom pure oxygen. For the method to ated, the gas was driven into a small cell unusual step of providing in the supplebe effective at environmental levels of on top of a photomultiplier tube. Ozone, mentary information [of the article] a list of every single part, including parts arsenic, chemiluminescence had to be generated from ambient air, reacted that cost $5, of the instrument and detected with a custom-built, state-ofwith arsine, and the resulting chemiluthe-art photodetector. minescence was measured by the photo- where you can buy them,” says Dasgupta. “We’ll provide assistance to nonprofAttempts to make the reaction more multiplier tube. it organizations to build it.” a practical were last described a decade Most importantly, Dasgupta and col—Rajendrani Mukhopadhyay ago. Then, it fell off the drawing board. leagues manipulated the reaction to 7362
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