Analytical Currents: Removing ambiguity

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News lowing the use of inexpensive acrylic color filters. Samples were held in a Plexiglass flow cell constructed so that the LED protruded into the cell. The sensor was powered with three 1.5-V batteries. The 0 2 concentrations obtained with the sensor disagree with those predicted by the classic Stern-Volmer model. The authors suggest that this may be a result of the trapped [Ru(dpp)3]2+ molecules experiencing an ensemble of microenvironments. The data werefitto a "two-site" model lhat assumes multiple Stern-Volmer quenching constants. The detection limits of the sensor for gaseous 0 2 are 0.5% 0 2 with the classic Stern-Volmer equation and 0.02% 0 2 with the two-site model. The sensor responds rapidly in the gas phase (~4 s from N2 to 0 2 and ~30 s from 0 2 to N2) The sensor is slower and less sensitive when measuring dissolved 0 in water. The response times are ~3 min (N to 0 ) and —10 min (0 2o N ) and the detection limit is 110 ppb. (AM Spectrosc 1998 52 750-54)

Looking for catalysts With combinatorial chemistry creating multitudes of products, the ability to screen rapidly is essential. But looking through large numbers of electrochemical catalysts has not been easy. Normally, testing involves measuring current as a function of potential—a process that becomes unwieldy with a very large number of samples. Now, Eugene Smotkin, Thomas Mallouk, and colleagues at Pennsylvania State University, Illinois Institute of Technology, and ICET have developed a way to find the needle in the haystack: optical detection. Regardless of the size of the array to be screened, optical methods are fast and simple. In addition, they make it possible to skim the less interesting parts of the array for outliers—useful members that are not closely related to those already known. Using a fluorescent indicator that detects the presence or absence of ions, the authors searched a small array of five elements—Pt, Ru, Os, Ir, and Rh—for new electrocatalysts for methanol fuel cells. The method revealed several good catalysts in parts of the array that did not look promising because they were bordered by inactive members. The search also identified a Pt-Ru-Os-Ir catalyst that performs significantly better than the previous frontrunner, an optimized Pt-Ru binary. (Sciencce998,280,1735-37) 504 A

Removing ambiguity daughter ion at m/z 157 as the base peak in their CEC/MS/MS spectra, the conditions Identifier tags have been suggested as a way to make decoding combinatorial librar- were optimized for this peak. The parent ion scan of m/z 157 can provide informaies easier. A typical method involves addtion about the standard tags and any impuing a series of secondary amines to the rities in the tag sample. beads that remain stable under the conditions used to release the library comThe method was demonstrated with tag pounds. The amines are then released by samples from single beads. In one case, an acid hydrolysis and derivatized with dansyl interfering peak that is co-retentive with chloride to make them fluorescent. Howone of the tags made decoding by HPLC/ ever, even this method can result in some fluorescence ambiguous, but CEC/ ambiguity when anomalous peaks appear MS/MS clearly showed that none of the in the chromatograms, possibly the result tag was actually present. (Rapid Commun. of residual combinatorial library compoMass Spectrom. 1998,12, 667-74) nents that were released and dansylated along with the tags. Stephen J. Lane and Adrian Pipe of Glaxo Wellcome (U.K.) resolve some of these ambiguities by coupling capillary electrochromatography (CEC) and electrospray MS. Because all of the dansylated amine CEC/MS/MS clears up the ambiguity in HPLC/fluorescence. (Adapted MH+ ions have a with permission. Copyright 1998 John Wiley & Sons.) NEWS FROM ASMS Celia Henry reports from Orlando, FL.

MS in space Size does matter, but it's not necessarily true that bigger is better. For space exploration, the goal is to make the instrument as compact as possible. Mahadeva Sinha and Stephen Fuerstenau described efforts at the Jet Propulsion Laboratory (Pasadena, CA) to miniaturize a mass spectrometer for space applications. To illustrate the challenges (and

the changing attitudes toward designing instruments for interplanetary research), Fuerstenau showed a photo of the GC/MS system from the Viking mission, which weighed in at 50 lb. The entire craft for the planned mission to Mars in 2003 will be only -150 lb. In fact, a mass spectrometer transported to Mars will likely have to weigh 1 1k (2.2 lb.) or less. Sinha describes the optimal mass spectrometer as a nonscanning type with an

The driftpath of the ROSINA RTDF. (Courtesy of Stefan Scherer.)

Analytical Chemistry News & Features, August 1, 1998