mance far outstrips that electrode analogs reveals of conventional memsignificant gains in perforbrane-based biosensors. mance. In tests with benchmark systems, the new senZhao says that they set sor offers faster measureout to construct a sensor ments (particularly at low that is compatible with a analyte concentrations), exwide range of biological hibits lower detection limits, components, applicable to and is linear over a wider various biosensing strateconcentration range. Accordgies, and easily incorpoing to Zhao and John, these rated into batch and flow improvements originate from formats. A random array the microdisk array. Very of platinum microdisks, low background currents are which forms the working Schematic of sensing system. reached several minutes afelectrode, is combined ter introducing the probe to with reference and auxilthe measurement solution, whereas, under iary electrodes into a single probe with a the same conditions, background currents planar sensing surface approximately 3 mm take hours to decay at a membrane-coated in diameter. The all-in-one design maintains macroelectrode biosensor. This means that a constant cell geometry, improves reprothe response time of the probe is much ducibility, and can be easily converted from batch to flow mode. A thin layer (—10 um) of shorter, and the S/N is greatly improved for measurements following brief equilibration strongly adhering, hydrophilic polymeric times. Moreover, at high analyte concentradispersion and an outer semipermeable hytions, the microdisk sensor response is dedrophilic dialysis membrane immobilize the pendent on membrane transport. As a result, biological moiety on the probe tip. the upper end of the linear range is similar Comparing the response of the new for die microdisk array probe and the analoprobe with that of membrane-based macro-
gous macroelectrode sensors. The net result is unusually long linear ranges at the new sensor—4 to 5 orders of magnitude are typical. To demonstrate the versatility of the probe, sensor formats based on single-enzyme, dual-enzyme, enzyme-inhibition, and immunosensing systems have been successfully implemented. These sensing strategies can be used for both batch and flow amperometric measurements; the latter gives additional flexibility by enabling easy control of the trade-off between sensitivity and linear working range. Advantages of the new sensor are highlighted in its application to the detection of phenols in organic media. With immobilized tyrosinase, the biochemical and electrochemical reactions occur witiiin a hydrophilic environment, and hence, the probe can be used directly in the organic medium without loss of enzyme activity and without problems of solution resistance. However, the probe is not merely convenient to use; with a 1-nM detection limit and a linear working range extending 5 orders of magnitude, the research group believes that it can be applied to a wide range of real analytical problems.
NEWS FROM THE AUTUMN MEETING OF THE NEW SWISS CHEMICAL SOCIETY Veronika R. Meyer reportsfromBasel, Switzerland.
Laser MS reveals urban air pollution City air is often polluted with toxic gases (e.g., CO, NO,, and 0 3 ) and dangerous aerosols. Are they emitted by diesel trucks, gasoline-powered cars, residential oil heating systems, or even open wood fires? Olivier P. Haefliger, Thomas D. Bucheli, and Renato Zenobi at the Swiss Federal Institute of Technology know the answer, at least for the particular sites where tiiey have collected samples. And they even know it with a
The traveling two-step mass spectrometer.
time resolution of 15 min, which enables them to monitor all the changes that occur between midnight and noon. The instrument that allows this quick on-site investigation is a two-step laser mass spectrometer. Aerosols are collected for 15 min on a quartz fiber filter. The deposited material is then desorbed with an IR laser pulse and selectively ionized by a UV laser pulse at a wavelength that is chosen in accordance with the excitation spectrum of the compounds under investigation. Every aerosol emission source exhibits characteristic tracer peaks, which show up in the mass spectrum. According to the researchers, diesel trucks produce alkylphenanthrenes (m/z = 192, 206,220, and 234), gasoline-powered cars yield alkylated N-containing polycyclic aromatic compounds such as alkylbenzocarbazoles (m/z = 231, 245,259, and 273), residential oil heating systems are disclosed by alkylphenanthrones (m/z = 222 and 236), and aerosols from open wood fires are clearly detected by the retene signal (m/z = 234 and numerous peaks at high masses). So far, the researchers have collected 1070 mass spectra at streets and parks in
the city of Ziirich. Using principal component analysis, they were able to identify the emission sources. Subsequent data processing allowed them to estimate the relative contribution of the various emission sources to air pollution. It is not a surprise that the truck signals were found to be lowest during the night and on Sundays. In Switzerland, truck traffic only is allowed on weekdays between 6 a.m. and 10 p.m.
Erratum In the recent Education article entitled "Instrumental Analysis at the University of Kansas" (Oct. 1 issue of Analytical Chemistry, pp 677 A-681 A), Herb Laitinen was inadvertently relocated to me University of Kansas during copyediting of the manuscript As most analytical chemists and long-time readers of this Journal know, Laitinen, a former editor of Analytical Chemistry (1966-1979), was a member of the faculties of the University of Illinois (19401974) and me University of Florida (from 1974 until his death in 1991).
Analytical Chemistry News & Features, December 1, 1999 791 A
