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Ion-pair reagents enhance SERRS LC coupled with vibrational spectroscopic techniques, such as FT-IR or Raman spectroscopy (RS), can provide unambiguous identification of unknown analytes. However, RS is not known for its sensitivity. That problem can be solved by using techniques such as surface-enhanced resonance Raman spectroscopy (SERRS), which, in some cases, offers better sensitivity than FT-IR. For example, trace amounts of dyes (150-750 pg) on a TLC plate have been detected using SERRS. Cees Gooijer and co-workers at Free University (The Netherlands) report on the separation and identification of four common dyes—basic fuchsin, ethyl violet, nile blue, and crystal violet—using
ion-pair LC-TLC-SERRS. The researchers focused on the effect of ion-pair reagents on the deposition of the dyes onto TLC plates and the resulting SERRS spectra. Dyes were separated by reversed-phase ion-pair LC, and the effluent was deposited onto a TLC plate using a spray-jet of heated nitrogen gas, which eliminated the solvent. The deposited effluent was then analyzed by SERRS. Nonvolatile ion-pair reagents (1-heptanesulfonic acid .C-TLC-SERRS setup. (Adapted with permission. Copyright 1999 The Roval Society of Chemistrv.) and sodium perchlorate) did not interfere with the deposition process or the SERRS spectra. In fact, were obtained for as little as 90 pg of higher SERRS intensities were observed dyes deposited on the TLC plate. .Anal. with the ion-pair reagents. Reliable spectra Conmun. .999,36, ,73-76)
NEWS FROM THE JOINT MEETING OF THE ASIA-PACIFIC BIOSENSORS GROUP AND THE AUSTRALIAN SOCIETY FOR BIOPHYSICS Alison Downard reports from Gold Coast, co-substrate demand", Pasco's group uses potassium ferricyanide instead. After a oneQueensland, Australial hour incubation of the microorganisms with the organic substrate and ferricyanide under Taking the O out a nitrogen atmosphere of 37 °C, the amount of BOD of ferricyanide reduced by the microorganisms is determined coulometrically, giving a Speeding up thefive-daybiochemical oxygen demand (BOD5) test by removing oxy- direct, calibration-free measurement of the amount of organic substrate oxidized. gen from the sample solution may sound illogical, but it's a strategy that works. The goal of the group's initial work was BOD5 is a widely used measure of the meto obtain the same amount of respiration in tabolizable organic content in water, which one hour as is obtained infivedays with relies on determining the amount of oxythe BOD5 method. Method development gen reduced by microorganisms over five was based on the BOD5 200 standard subdays as organic material is consumed. strate, which, in the 5-day test, results in There is a lot of interest in decreasing the the reduction of 200 mg 0 2 /L, correspondtime required for a result, and Neil Pasco ing to a 62.5% conversion of the substrate. and co-workers at the Lincoln Ventures By keeping the concentration of ferricyalaboratories of New Zealand's Lincoln Uni- nide high (and in excess), the number of versity believe that eliminating oxygen bacterial cells could be manipulated to give from the system is the best way to do that the required rate of substrate consumption. The principle has been demonstrated using According to Pasco, the standard test Escherichia coli, but other microorganisms requires five days because of the relatively are under investigation. Pasco anticipates low solubility of oxygen in water and the correspondingly low levels of bacteria that cocktail of monocultures will give the are used. Oxygen acts as the terminal elec- best results wide range of sample tron acceptor for microbial respiration, and types Also under investigation is the imhence, they reason that replacing oxygen mobilization of bacteria which greatly simwith a more soluble synthetic co-substrate plifies their handling and recovery from the should allow higher numbers of bacteria to reaction mixture be used, reducing the incubation time. Pasco points out that they chose to emulate the BOD5 standard result (62.5% converIn the new method, called "biochemical 790 A
Analytical Chemistry News & Features, December 1, 1999
sion of BOD 200 substrate) to demonstrate the concept of biochemical co-substrate demand, but measurements could be based on a much smaller percentage conversion following a much shorter incubation period. Sensitivity would not be a problem. For example, using 3 mL of BOD 220 standard, a 1-h incubation generates 120 umol of ferrocyanide, which corresponds to almost 12 coulombs of charge in the detection step. Clearly, it should be possible to reduce the percentage conversion significantly and maintain high reliability in the measurement step. This suggests that very rapid tests may be possible, and Pasco is enthusiastic about developing the system into a device for rapid BOD determination with applications for near real-time process control.
All-in-one biosensing probe Ask biosensor researchers what they look for in an electrochemical sensing system, and, chances are, the features will be found in the all-in-one, dual batch and flow mode membrane-based probe designed by Huijun Zhao, Richard John, and student Shanquing Zhang of Queensland's Griffith University. The group claims that not only is their probe extremely versatile and easy to use, but in many cases, its analytical perfor-
