giving superior precision performance is the Columbia Scientific Industries—Stone Thermal Analyzers. SENSITIVITY: .0016°C per inch TEMPERATURE RANGE:-160°C to 1600°C with DTA -160°C to 1000°C with DSC FLEXIBILITY: Wide range of sample holders that allow use of a variety of sample holder materials (aluminum, stainless, nickel, paladium, platinum) and configurations (exposed, post, ring, bipod) of thermocouples. Plus 4 different types of thermocouples and in addition special holders are available to provide high pressure (3000 psig) and high vacuum (10- i Torr) operation. All sample holders provide true dynamic atmosphere control with all gases. EASE OF OPERATION: The design of the Stone DTA-DSC Systems makes changing samples, sample holders etc. a simple task.
STABLE BASE LINE: Maxium drift of baseline is 5 microvolts which preceeds the need for baseline compensation. QUALITY OF DESIGN & CONSTRUCTION: The Stone Systems have been evolved over the years with extreme care in design and construction to provide the highest quality product. ACCESSORIES: A variety of accessories such as EGA, TGA, Time base generators and Derivative Computers. You cannot miss with this perfect formula in Thermal Analysis let the CSI-Stone Thermal Analytical Instruments work for you.
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Analytical and Industrial Division
COLUMBIA SCIENTIFIC INDUSTRIES
P. O. Box 6190 / Austin, Texas 78762 / (512/926-7850)
CIRCLE 43 ON READER SERVICE CARD 1026 A · ANALYTICAL CHEMISTRY, VOL. 45, NO. 12, OCTOBER 1973
scanned mechanically with a slow speed motor and gearbox. The electrostatic sector voltage, set at say, 500 V, can be scanned by using this arrangement at any prechosen rate from 0.003 to 10 V/min. This mechanical system of scanning has the advantage that the starting position and range of any scan are extremely reproducible, and it is therefore suitable for use with a computer-controlled system. The alternate system uses a highvoltage operational amplifier approach. The positive sector supply is generated by an Analog-Devices, Inc., Model 180 amplifier, zener coupled to a high-voltage pass transistor. A wirewound, low-temperature coefficient, feedback resistor is used to connect the output to the amplifier summing junction. A reference voltage is fed to the summing junction to set the initial sector voltage, and a scan ramp is also applied to this junction during electronic scanning. The resulting amplifier has a gain of 32; 10-V input produces 320-V output. The negative sector supply is based on a similar system with a gain of — 1.0000. The input to this inverter is the output of the positive supply. Thus, tracking is assured and both supplies vary equal amounts from signal common, which is spectrometer ground. Scanning may be accomplished with several types of ramp generators. These include the following: an operational amplifier integrator circuit, a Solion (Self-Organizing Systems, Inc., Dallas, Tex.) electrochemical cell ramp generator, and a computer via a D to A convertor. The magnet coils are driven by a modified supply originally manufactured by Hitachi Ltd. for use on their RMH-2 mass spectrometer. It can deliver up to 4 amps of current at 80 V which, with the magnet coils connected in parallel, enables a mass of 450 to be transmitted at an ion-accelerating voltage of 8 kV. Higher masses can be studied at the same current if the coils are wired in series. Stability of the magnet and source supplies is sufficient after an hour's warm-up to set the mass analyzer on to any mass peak and have it maintain this setting for a period of days. The ion beam is measured with 16 stage electron multipliers Model R474 manufactured by Hamamatsu Co., Ltd. One of these is fixed in position behind the final collector slit; the other is mounted on a vacuum bellows assembly and can be lowered into position behind the intermediate slit when it is required to plot a mass spectrum or to select a mass peak for subsequent energy analysis of its fragmentation products. Having selected a mass peak for study, the multiplier is
