pendent of the collection optics. By including dielectric longpass filters in combination with a single monochromator, they achieved four-fold greater efficiency than would be possible with a triple monochromator, in spite of large losses caused by the filters. With the current instrumental configuration, they achieved a spatial resolution of approximately 3 x 9 um in die
lateral plane and 10 um or less in the axial plane. They used this system for the analysis of chemical vapor-deposited diamond films, calf-thymus DNA and a single Paramecium macronucleus. The authors were also able to resolve the components of the nondiamond carbon bands in CVD diamond films. (Appl. Spectrosc. 1997,51,81-86)
Explosive measurements As the United States closes military bases, one of the problems to be dealt with is groundwater contaminated with explosives such as trinitrotoluene (TNT). The current method of analyzing water for TNT is EPA's SW846 Method 8330 (based on HPLC), which can take up to one month and cost as much as $1000. Frances S. Ligler and colleagues from the Naval Research Laboratory and Geo-Centers investigated alternative method that uses a portable fiber-ODtic biosensor for groundwater monitoring The authors reported a detection limit (without sample precon-
Contour maps of TNT groundwater contamination determined by the fiber-optic biosensor versus the EPA Method.
Coming in for a soft landing Surface modification, used to control chemical and physical properties, is important in areas such as electronics, catalysis, and electrochemistry and is usually accomplished with high-energy ion beams. Graham Cooks and his co-workers at Purdue University and 3M Corporate Research Labs have used a low-energy "soft landing" technique to modify fluorinated self-assembled monolayers (F-SAMs) with the sterically bulky silyl ether ion, (CHo) ,SiOSi(CHo) ?. The ions were mass selected, decelerated to 10 eV, and allowed to collide with the surface. The method exploited the ability of MS to control the interaction energy, dose, and isotopic composition.
centration) of 20 ug of TNT/mL a 16-min run time, and an esttmated cost of $3 a sample. The fiber-optic tip was coated with an antibody that recognized TNT via a competitive fluorescent immunoassay. Fluorescent evanescent wave sensing, using 635-nm laser light, monitored the immunoassay reaction. As many as four fiberoptic probes were simultaneously monitored With this system the authors investigated samples from monitoring wells at two military bases comparing the results with values determined by the EPA method (Environ. Sci. Technol. 1997, 31 827-41)
The F-SAM surface was examined with 60-eV 132Xe*+ sputtering before and after the deposition of the ether ions. The total ion dose required to saturate the surface was 1 x 1013 ions, which corresponds to ~ 7% of a monolayer. The only new ion in the mass spectrum was at m/z 147, indicating that the ions were trapped intact and could be successfully retrieved. The ions could not be easily removed by chemical reaction, possibly because of the hydrophobic F-SAM matrix and the steric bulk of the ion. The authors suggest that the soft landing method will be useful for positioning polyatomic ions near metals to study spectroscopic effects and for preparing surfaces with unusual electronic and magnetic properties. (Science 1997,275, 1447-50)
GOVERNMENT
ATP for analytical systems The latest round of projects winning funding from the U.S. Department of Commerce's Advanced Technology Program (ATP) includes two proposals for analytical systems. The projects are funded for two years. CuraGen (Branford, CT) plans to develop a "practical nanoscale molecular pump" capable of separating molecules by mass. The envisioned device will use an array of etched microchannels to guide molecules over a linear array of electrodes. Modulating the electrodes forces molecules to migrate through the channel, with the lighter molecules moving faster. Separations take place in a homogenous solution, avoiding gels or other special media typical of electrophoretic techniques. An important application will be the separation of DNA molecules. CuraGen will receive $2.0 million in ATP funds and plans to spend more than $14 million of its own funds on the project Nanogen (San Diego, CA) is developing a portable genetic analysis system for use in forensics, identifying trauma victims, or detecting pathogens. The system would extract DNA from blood or tissue, fragment the biopolymer, and make identifications based on genetic polymorphism. The device will include a disposable fluidics module, an integrated assay chip, and a multichip detection and control module to analyze assay results. The ATP will provide $2.0 million toward development, and Nanogen expects to add about $1.9 million of its own funds
EPA proposes flexibility In March, EPA's Office of Water (OW) formally proposed an approach to introducing "flexibility" in what analytical methods are acceptable under the Clean Water and Safe Drinking Water Acts (Federal Register 11997 62,14976-15049). The proposal would give analysts greater latitude in modifying EPA's approved methods or creating new ones. It is also being touted as a streamlining move that reduces the regulatory burden on purchasers and suppliers of analytical data. However, states have the final say on what is acceptable and can choose to accept analyses that follow only the prescribed procedures found in EPA's approved methods.
Analytical Chemistry News & Features, May 1, 1997 2 8 3 A
News Theflexibilityproposal follows months of discussion between OW and the affected community, and comes as a concerted effort—within and outside the agency—is underway to change EPA's approachtoanalytical methodologies (see Anal. Chem. 1996,68,733 A-37 A). In theory, flexibility could lead to less expensive analyses and spur the sale of new types of analytical instrumentation. The OW proposal, however, falls short of what some see as the ultimate goal of introducing performance-based methods that give analysts the freedom to use any method that meets certain data quality objectives and quality controls. Comments on the proposal are due to EPA this month
PEOPLE
King wins Wiley Award Jerry King, lead scientist at the USDA's National Center for Agricultural Utilization Research, has been awarded AOAC International's Harvey W. Wiley Award for significant advances in analytical methodology. Wiley was instrumental in establishing laws protecting the purity of foods, drugs, and cosmetics. King is being honored for his work in SFE and SFC with compounds such as lipids, pesticides, volatiles, and semivolatiles. The award carries a cash prize and King will speak at a symposium in his honor at the association's annual meeting in September
Benedetti-Pichler nominations The American Microchemical Society requests nominations for the 1998 BenedettiPichler Award, which recognizes outstanding achievements in microanalytical chemistry. The award consists of a plaque and expenses to attend the Eastern Analytical Symposium in Somerset, NJ, in November, to receive the award. Eligibility is not restricted to society members, and past nominees may be renominated with updated information. Documents should include three nominating letters and should be sent to Robert G. Michel, Dept. of Chemistry, University of Connecticut, 215 Glenbrook Rd. Storrs CT 062694060 (860-486-3143;
[email protected]). The deadline is Oct 24 284 A
Michael Tswett and his method This month marks the 125th anniversary of the birth of Michael S. Tswett, who first developed chromatography in the early part of this century. Tswett, a botanist by training, was interested in the chemical composition and biological function of plant pigments. To study these materials, he needed a simple method to separate the pigments—simpler than the complicated liquid-liquid partition procedures being used. Tswett's papers clearly indicate that he performed numerous separation experiments to find suitable phase systems for his new technique based on adsorption phenomena. Nevertheless, there are only three publications in which he described the work: a 1903 lecture presented in Warsaw, Poland (Proc. Warsaw Soc. Nat. Sci.c Biol. Sect., 1903,XIVN.. 6); a 1906 paper (Ber. Deut. Bot. Gesellsch. 1906624,384); and d 1910 book on biological pigments (Khromofilly v Rastitel'nom i Zhivotnom Mire (Chromophylls in the Plant and Animal World) Karlassiakoff Warsaw 1910). The Warsaw lecture gave the first description of the new technique but without illustrations. Tswett outlined a ligroin extraction of green leaves (e.g., dead nettle or plantain) and elution of material on a bed of inulin: "First, a colorless liquid flows out from the bottom of the funnel (i.e., the glass column), then a yellow one (carotene), while a bright green ring forms at the top of the inulin column below which a welldefined yellow ring appears soon. On subsequent washing of the inulin column with pure ligroin both rings the green and the yellow one are considerably widened and move down the column" The inulin powder is a carbohydrate with a 2-um particle diameter; the column was packed dry, and the separation process took place "under slight pressure or suction". The separation performance was high enough to obtain the yellow eluate as a pure solution whose identity was proven to be xanthophyll alpha by UV-vis spectroscopy. The green ring could be further separated into two zones of deep bluegreen and yellow-green. Tswett must have been a skillful experimenter to dry-pack a 2-um powder with the necessary homogeneity for well-defined and undisturbed chromatographic bands In the 1906 paper, Tswett brought his method to a markedly higher performance. He recommended using calcium carbonate or sucrose as adsorbents for plant pigment separation. In the paper, he wrote: "Like
Analytical Chemistry News & Features, May 1, 1997
Michael Tswett
light rays in the spectrum, the different components of a pigment mixture, obeying a law, are separated on the calcium carbonate column and can thus be determined qualitatively and quantitatively. I call such a preparation a chromatogram and the corresponding method the chromatographic method." (Perhaps Tswett was playing witii words: "chromatography" means "color writing", and the Russian word "tswef' means "color".) The paper was accompanied by a drawing of a chromatogram showing the separated, although not yet eluted, bands of three xanthophylls and two chlorophylls (the carotenes were not retained by the stationary phase but eluted with the solvent front). The drawing revealed that the green plant pigment, chlorophyll, consists of two compounds. Tswett's work with plant pigments, however, was not accepted by the "authorities" of the time, Richard Willstatter and Leon Marchlewski. The latter condemned the chromatographic method as a "filtration experiment", which was too simple to yield scientifically sound results. In retrospect, recognition for the new technique was probably hampered because Tswett's separations could be reproduced only by careful and patient researchers. The traditional partition methods on the other hand were tedious but easier to perform. The 1910 book dealt mainly with plant physiology. In a short section, Tswett again described his chromatographic experiments but without presenting any new details of the technique. In fact, when his procedure is examined step by step, it is not really clear how he obtained his separations. He seems to have preferred step-gradient elution in which more than one solvent is used for the development of the chromatogram.
