Channeling electrochemical detection Relatively few compounds of biological relevance fluoresce effectively. This problem limits detection schemes for techniques like channel electrophoresis, a continuous sampling and electrophoretic separation method with time resolutions of a few seconds. Electrochemical detection is an attractive alternative to fluorescence because of its high sensitivity (10~19 mol), previous successes in single-cell studies, and the widespread application of microfabricated electrode arrays in LC. In addition, many compounds of biochemical interest are easily oxidized, avoiding the problems associated with derivatizing in nanoliter to picoliter environments Andrew G. Ewing and Peter F. Gavin of Pennsylvania State University described an array of platinum microelectrodes that were fabricated by microlithography as an electrochemical detector for channel electrophoresis The electrode array detector consisted of 100 individually addressed electrodes spaced across the channel exit to provide location-based as well as temporal amnprometric response for i mi..,.• ross the exit of the
narrow channel. Each electrode was 95 pm wide and 0.12 pm high with h uru of space between adjacent electrodes. A 1-um-thick layer of Si02 was chemically deposited by plasma- enhanced chemical vapor deposition over the connection pathways for insulation. The channels had an internal height of less than 25 pm, which reduced the separation currents generated in the electrophoretic process. Moreover, because of the increased internal resistance of the structure, the majority of the separation voltage was dropped across the channel length, leaving a minimal potential field at the exit of the channell Therefore, the working electrodes were not dramatically affected by the separation potential, and isolation was not necessary. In a test of the system, a mixture of dopamine and catechol was continuously deposited over 5 min across the channel entrance by moving the sampling capillary along its width in 0.6-s time increments. Although zone broadening occurred, no attempt was made to optimize the separation, and the analytes were clearly and continuously resolved. The amount of dopamine injected per step was ~ 700 fmol, corresponding to 3.5 pmol across each electrode. The mass detection limit calculated for dopamine at electrode 50 was ~25 fmol which is promising for single
Getting the dirt on humic substances Understanding the chemical and physical behavior of humic substances and their interactions with environmental contaminants is essential for elucidating their impact on the fate, bioavailability, and toxicity of organic and metal contaminants. Unfortunately, the heterogeneity of humic substances makes determining their structural and conformational character challenging. However, the intrinsic fluorescence of humic substances could provide information that relates structure conformation heterogeneity, and dynamic properties. Total luminescence spectroscopy provides a complete representation of the fluorescence spectral featuree so f aample in the form of an excitation-emission matrix (EEM) in which fluorescence intensity is presented as a function of excitation wavelength on one axis and emission wavelength on the other. Linda B. McGown and colleagues at Duke University used total luminescence spectroscopy on samples obtained from the International Humic Substances Society (IHSS) to characterize and compare aquatic- and soil-derived humic substances and described the effects that concentration ionic strength and pH have on the spectra.
ctJil CAjJCr 1~
ments in which a tvoical nerve or hormonal cell contains femtomole lev IT
Channel electrophoresis scheme* shown with five electrodes, connections, and bond Dads.
hydrophilic surfaces. Using the adhesion between methyl groups in water, they estimated an effectivetipradius of ~ 30 nm and contact area of ~ 10 nm2 (~ 50 contacting molecules). Because solvent exclusion regulates adhesion between these model
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ger. (/. Am. Chem. Soc. 1 QQfi 7 IS
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organic surfaces, it provides a source of chemical contrast in force imaging, which they explored with friction force measurements of co-block kolyethylene glycol-polyamide polymer surfaces. (J. Am. Chem. Soc. 1996,118,8925-31)
Absorbance-corrected EEMs of two soil-derived humic substances.
Analytical Chemistry News & Features, December 1, 1996 715 A
News The researchers found that ionic strength in the range of 0-1M KC1 aad humic substance concentrations of 5,50, and 100 mg/L had little effect on fluorescence spectra characteristics. However, increasing pH caused a red shift in the longer wavelength peak region. These spectral shifts may have reflected changes in the conformations of humic molecules at different pH. Fluorescence intensity also increased as pH increased; ; pH of 6 provided significant discrimination among most humic substances. Their results also indicated that total luminescence spectra can be used to discriminate between aquatic-derived and soil-derived humic substances and between humic and fulvic acids from the same aquattc or roil source. Humic acids had ffuorescence maxima at longer excitation and emission wavelengths than the corresponding fulvic acids from the same source. A red shiit in the fluorescence maxima in the humic acids selative to the fulvic acids from simiiar sources was attributed to the presence of high molecular weight fractions, electron-withdrawing substituents, and a higher degree of conjugation in the humic acids. Electron-donattng substituents in the fulvic acids contributed to the relatively short wavelengths of the fluorescence maxima. The fulvic acids were generally more intensely fluorescent than the humic acids and fluorescence spectral maxima of the soil samples are at longer excitation and emission wavelengths than those of the aquatic samples. (Environ. Sci. Technol. 1996,30,3061-65)
Web sightings Finnigan Corporation—http://www. finnigan.com. Includes company background, product information, training schedules, employment opportunities, and an online version of the user newsletter. Chemists' Club Library—http:// members.aol.com/chemists/ccl.htm. Includes information on the history of the library, services, holdings, free publications, ordering documents, and prices. Scientific Instrument Services— http://www.sisweb.com. Includes a company overview, detailed product and service information, application notes, and links to other MS-related sites.
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BUSINESS
Perkin Elmer acquires Spectro Perkin Elmer's Analytical Instrument Division has agreed to acquire the stock of Spectro Gelleschaft fur Spektrometrie GmbH, a manufacturer of analysis techniques for solids. In particular, Spectro brings to PE proprietary technology for arc/spark and X-ray fluorescence techniques. Spectro was launched in 1979 and last year had more than $80 million in sales; the company employed approximately 500 people. PE says it plans to maintain Spectro's principle business operations.
Bio-Rad buys SoftShell Bio-Rad Laboratories has acquired software vendor SoftShell International, known for its ChemWindow and ChemIntosh drawing software. SoftShell will be incorporated into the Sadtler Research Division under manager Richard Moore, who will work with former SoftShell president Craig Shelley to create new products by combining Softshell's component software for handling structures in commercial relational databases with Sadtler's spectroscopy components. Sadtler and SoftShell will continue development and support of their current products.
ESM Software—http://www.esm-software.com. Materials software directory includes descriptions of software related to the science, chemistry, and processing of metals, ceramics, and polymers. Demonstration copies of many programs can be downloaded from the site. Spectra-Tech—http://www. spectratech.com. Includes information on IR sampling accessories, microscopes, and supplies for FT-IR spectrometers, along with information on training classes and technical events. Drug Information Association— http:// www.diahome.org. Includes information on membership, publications, upcoming meetings, an online version of the Drug Information Journal, and links to related sites.
Analytical Chemistry News & Features, December 1, 1996
Varian acquires Rainin HPLC line Varian Associates has announced that it will purchase the HPLC assets of Rainin Instrument for an undisclosed amount of cash. The acquired products have been manufactured at and distributed from Rainin's facilities in Emeryville, CA, and Woburn, MA, which are not included in the transaction. Varian says that it plans to offer positions to most of the 60 Rainin employees involved. According to Varian Executive Vice President Allen J. Lauer, who heads the company's instrument business, Varian's previous LC efforts have traditionally been aimed at higher end R&D and method development laboratories, and the addition of Rainin's lower priced HPLC line will expand the company's market into the broader QC area. In addition, says Lauer, Varian has not participated in the preparative HPLC or specialized columns markets, and the addition of Rainin's products addresses both of these broad markets. Rainin plans to focus on its pipette and liquid measurement businesses in which it is a market leader.
ThermoQuest buys t w o businesses from parent ThermoQuest has announced the purchase of CE Instruments (Milan, Italy) and MassLab Instruments (Manchester, England) from its parent, Thermo Instrument Systems. ThermoQuest will pay Thermo Instrument $19.8 million for CE Instruments, a European manufacturer of GC instruments, and $6.6 million for MassLab, formerly VG MassLab, which produces a llne of benchtop quadrupole mass spectrometers for GC and LC appllcattons. The two companies were part of the Scientific Instruments Division of Fisons pic acquired by Thermo Instrument in March 1996. According to ThermoQuest president and CEO Rick Chapman, the acquisition of CE Instruments, founded in 1953 as the scientific instruments division of Carlo Erba S.p A, gives the company a much stronger presence in key European markets, whereas the acquisition of MassLab Instruments, combined with the recent acquisitions of Automass and Extrel FT/MS, gives ThermoQuest a much broader MS product line. The two new companies join Finnigan and Thermo Separation Products in the ThermoQuest family of companies.
