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 to N ). 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 c199 85 750-54)
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. (Sciencc 1998,280,1735-37) 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 wiil be only -150 lb. In fact, a mass spectrometer transported to Mars will likely have to weigh 1 11 (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
would provide a specific assay for Cryptotime a highly sensitive assay for infecsporidium, ,nd ESI would dffer the edditious Cryptosporidium. tional benefits of enhanced sensitivity and To their disappointment, repeated Although the mention of microorganisms reduced sample preparation. Burkhalter applications of this methodology recan conjure up images of biological weap- set out to find the endogenous phosphovealed that the unique fatty acid was, in lipid, which was previously thought to be ons or terrorist attacks, microorganisms actuality, an artifact added occasionally acylated at the sn-2 position of phosphatiare more likely to affect the average perfrom amber rubber bulbs in the extracson in food or water. The protozoan Cryp- dylethanolamine. However, parent ion tion/purification procedures. This findtosporidium has been particularly difficult scans revealed the presence of no signifiing was unfortunate because the identicant precursors. Neutral mass loss scan to detect with the sensitivity needed to fication oo an axtremely unusual fatty revealed that no phosphatidylethanolamine acid unique to species of Cryptosporidprotect human health. One of the challenges is in differentiating infectious from was present in the fraction containing ium would have allowed for the detecnon-infectious Cryptosporidium, espe- 10-OH 18:0. tion of this opporrunistic pathogen, cially when 20-30 oocysts has been such as a water distribution system's Burkhalter and co-workers eventually identified as an infectious dose. D. C. biofilms, without the prerequisite of determined mat 10-OH 18:0 did exist in White Rob Burkhalter, and co-workCryptosporidium samples, but as a sree fatty oocyst purification and identification. ers at the University of Tennessee are acid, which is extremely rare in nature. Despite the artifactual nature of working on a mass spectrometric Low-energy collisionally induced dissocia10-OH 18:0, the research showed that it method for distinguishing infectious tion conditions for the selected reaction is possible to differentiate infectious and and non-infectious species. Their monitoring (SRM) of daughter ions of non-infectious Cryptosporidium parvum, search for a uniaue biomarker has 10-OH 18:0 were optimized for the produc- as well as differentiate C. parvum from been interesting, but so far unfruitful. tion of ions diagnostic of the site of hyother species of Cryptosporidium and EiHowever, they have been able to use droxyl substitution. It was found that under meria through hierarchical cluster analycluster analysis to differentiate species these low energy conditions, highly spesis of lipid patterns from purified oocysts. of Cryptosporidium. cific fragmentation processes were occurThe current problem is the difficult purifiring, which provided in a much more sen- cation procedures required to isolate Earlier studies had seemed to link a Cryptosporidium from other waterborne novel fatty acid, 10-OH 18:0, to Crypto- sitive SRM assay because of the lesser microeukaryotes whose lipid patterns sporidium parvum. Burkhalter and dis extent of nonspecific fragmentation typical of high-energy CID studies. This reobscure those of infectious Cryptosporidco-workers had hoped to transfer the sulted in a highly sensitive and specific ium parvum. For these reasons, efforts methodology for detection of the susassay for the presence of 10-OH 18:0 in continue toward identifying unique biopected biomarker to HPLC/electrospray complex biological matrices and thus it marker patterns for Cryptosporidium and MS. Identification of the endogenous was thought to have provided for,the first other non-culturable pathogens phopholipids containing 10-OH 18:0
Going after Cryptosporidium
array detector for the simultaneous measurement of different mass ions. He has developed a miniature mass spectrometer of Mattauch-Herzog geometry, which is just 10 x 5 x 4 cm. .t measures ions up to 240 m/z, possesses a resolution of >300, and consumes only 1-2 W. Two kinds of array detectors have been developed. The first is based on an ion-electron-photon conversion process. The ion images are measured with a photodiode or a CCD array. The second approach employs a multianode system, which is fabricated along wiih pulsecounting electronics on a silicon chip. In addition, efforts are being made at other institutions to design mass spectrometers for cometary research. The International Rosetta Mission, sponsored by the European Space Agency and slated for launch in January 2003, is expected to deploy a spacecraft that will rendezvous with comet 46 P/Wirtanen and escort it for two more years. Hans Balsiger, Stefan Scherer, and co-workers at the University of Bern
(Switzerland), the Southwest Research Institute (Austin, TX), the Max-Planck Institut fur Aeronomie (Germany), and the University of Giessen (Germany) described a prototype reflectiontime-of-flight(RTOF) mass spectrometer that will be part of the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) package. The package will also include a double-focusing mass spectrometer and a "neutral dynamics monitor". The RTOF is ~ 1 ml with a flight tath oo 2 m when ions are reflected only once. The design also incorporates a "hard mirror" that can effectively double the flight path. The hard mirror consists of three cylindrical elements and a shaped backplane which can be used to remove selected mass lines by applying a positive pulse to the backplane electrode Mass resolution of up to 5700 (132Xe) has been achieved and the mass accuracy is —10 oom The RTOF is compact only 1134 x 309 x 252 mm and 10 4 kg It consumes 13 4 W in the low nower mode and 23 0 W in the full operation mode
GOVERNMENT AND SOCIETY
Eggsacting standards A review by U.K. government scientists of techniques used to estimate veterinary drug residues, such as ionophores for preventing coccidiosis in poultry, has shown there to be no reliable way of correlating residue levels with duration or amount of medication or whether there has been any cross contamination or misuse of the drugs. Christopher Elliott and colleagues at the Veterinary Sciences Division in Belfast, a European Union drug-residues monitoring unit, say that with the current analytical methods there is no satisfactory way to determine residue levels of all of the widely used ionophore drugs in the poultry industry. "MRLs [maximum residue limits] do not exist for these drugs [the ionophores]
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