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These three new models of variable speed stirrers are electronically controlled and are designed to handle a range of viscosities. Available speeds range from 0 to 6,000 rpm. All three models feature overload protection with a manually resetable circuit breaker. The shaft and propeller are made of stainless steel for easy cleaning and resistance to most acids and chemicals. Arrow Engineering. Featuring more than 65 chemicals available in high purity, reagent and technical grades, this 1988 catalog includes such specialty chemicals as germanium compounds, purified carbamates, silanes, industrial intermediates, high-purity inorganic compounds and organometallics. The company offers custom chemical synthesis and a free evaluation of a potential client’s proposed synthetic route for compounds for which bids are being solicited. Hach Synthesis, Inc. Centrifugal partition chromatography (CPC) is a liquid chromatographic technique that employs liquid/liquid partition counter/ current distribution to fractionate complex chemical mixtures. This technique is particularly advantageous for isolating polar substances and biologic materials, such as pharmaceuticals, biopolymers, antibodies and genetically engineered molecules. The model LLN-5 CPC system requires no solid stationary phase; stationary phase solvents are retained in the column by the action of centrifugal force. The mild operating environment reduces the potential for denaturation and decomposition of sample components. Centrifugal partition chromatography is compatible with any two-phase solvent system. Sanki Laboratories, Inc. Featuring 14 software programs written exclusively for use with the TEF System 12 acoustic analyzer, this free catalog describes each software package and its specific advantages. This new software expands the TEF system’s capabilities, making it useful for testing virtually any audio environment. Included in the catalog are descriptions of 3D Reverb, which generates RT6O times from S.D TEF measurements; Version 2.OA TEF system 12 analysis, which provides advanced measurement capabilities; Autotef, which allows for automation of repetitive tests; and Workbench, which implements four instruments—sound level meter, digital voltmeter, digital oscilloscope and function generator—on the TEF analyzer. Techron. Helium-neon laser gas mixtures that incorporate the stable isotopes helium-3, neon-20 and neon-22 are available in either stainless or carbon steel cylinders ranging in size from 0.4L-8L. These customized mixtures meet the clients’ specifications for chemical and isotopic ratios, pressures and total quantities. Gas chromatographic and mass spectrometric analyses accompany each mixture, detailing the isotopic ratio and chemical impurities. The helium-3 is available in standard, chemical and isotopic grades. Isotec, Inc. The Prime-a-Gene labeling system yields high specific activity probes of greater than lO5cpm/ug of DNA, using amounts of DNA as small as 10 ng. Working with DNA fragments cut from agarose gels, Prime-a-Gene uses the Klenow fragment of DNA polymerase I to extend hexadeoxyribonucleotide primers that have hybridized along the length of the denatured DNA template. Incorporation of more than 70 percent of the labeled deoxyribonucleotides is common. Promega. The Dual Promoter Cloning Pak allows subsequent transcription by either T7 or SP6 RNA polymerase in RNA probe production. The vectors pDP-1 and pDP-2 each contain both promoters, a multi-cloning site with 11 unique restriction enzyme sites in opposite orientation, an ampicillin resistance gene and a high copy number origin of replication. The kit also includes T4 DNA ligase and ligase reaction buffer. Du Pont Co. The A160 benchtop unit performs concentration, evaporation, sample reduction, and drying functions. Digital controls allow the user to regulate the pre-set endpoint dryness, chamber heat and the externally supplied vacuum. The unit features a chemical trap for neutralizing acids and absorbing radio active isotopes, and a refrigerated vapor trap witha 4L glass insert for collecting condensate. Rotors for tube sizes range from 0.4 mL to 16 mL. The A160 yields 100 percent solute recovery with no cross contamination. Savant Instruments, Inc. Ideal for measuring open circuit membrane potential and membrane resistance of epithelial membranes, the EVOM millivolt and ohm meter uses isolated alternating current (± 20 ug at 50Hz). This device offers several advantages: the zero net charge of the alternating current does not adversely affect the epithelial membrane; there is no deposition of electrode metals (often caused by direct current); and resistance readings are unaffected by membrane capacitance. The EVOM electrodes are rigid plastic tubes with a central Ag/AgCI voltage sensor electrode and an annular silver electrode at each tip for passing current through the membrane. World Precision Instruments. Filter Tips Vanderkamp Full-Flow polypropylene filter tips are 1/2 inch long and 1/4 inch in diameter. They feature a two-step interior with a 1/8 inch opening at one end for improved flow, easy attachment to cannulas or pipettes and removal of multiple samples with one filter. These disposable filter tips are available in 10 and 35 micron porosity. VanKel Industries, Inc. Electronic digital micrometers now accompany the company’s precision positioning stages. The micrometer provides a LCD position readout to a resolution of one micron, and offers incremental or absolute positional modes of operation. Designed to achieve straight-line accuracy of ± 0.00005 inches/ inch and repeatability of ± 0.00005 inches, the positioning stages offer load-carrying capacities from 44125 pounds. Prices for these positioning systems range from $299 to $365. Daedal Inc. Summit automated sample preparation system offers custom-designed software for efficient collection, storage and reporting of test data as well as quality control monitoring. Designed for use in blood banks, the system can load samples from primary specimen tubes to microplates or well-trays and can aspirate and dispense selectively from up to 12 microwell samples simultaneously. The disposable pipette tips are automatically changed and loaded onto the pipetting head according to the instructions contained in the software. Automatic scanning by a barcode reader ensures sample and microplate identification throughout the testing process. Du Pont. (The Scientist, Vol:2, #2, p.23, January 25, 1988) (Copyright © The Scientist, Inc.) WE WELCOME YOUR OPINION. IF YOU WOULD LIKE TO COMMENT ON THIS STORY, PLEASE WRITE TO US AT EITHER ONE OF THE FOLLOWING ADDRESSES: editorial@the-scientist.com or The Scientist, 3600 Market Street, Suite 450, Philadelphia, PA 19104, U.S.A.

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