Converting the Aminco™ DW-2 Optical Spectrophotometer

Since the mid-1980s, OLIS has offered a modernization procedure for the AMINCO™ DW-2 series¹ of spectrophotometers. This modernization removes everything that dates the instrument and adds sophisticated computer control. The decision to modernize is one of two choices for adding the best optical bench to your laboratory for the study of highly turbid samples².

The AMINCO™ DW-2 spectrophotometer includes two modified Czerny-Turner monochromators with 600 lines/mm gratings blazed at 300 nm; the monochromators can be coupled together or used independently. The detector is a large end-on photomultiplier tube positioned immediately adjacent to the sample. The sample compartment has two positions for the sample (for dual wavelength and split beam). A quartz diffuser plate can be used or not.

The spectral range of 200-850 nm is extendable to 1200 nm with use of red sensitive photomultiplier tubes; the spectral resolution is 0.2 nm, readable to 0.1 nm. Modes of operation remain split-beam, dual wavelength, and dual wavelength scanning; the derivative mode, known to result in the wrong answer, is not retained. (The high speed kinetics mode of the original Aminco is also not available in the Olis modernized system, since the new synchronous motor cannot be used at high speed.) Light sources are deuterium and tungsten lamps that can be turned on simultaneously; a selector switch controls which source enters the monochromator(s). Two continuously variable optical attenuators are used for balancing the two beams in the dual wavelength and the split beam modes. Drift is < 0.0005 AU/hr, stray light is better than 0.2% at 200 nm, maximum noise level is 0.0002 AU, and optical resolution is better than 3 Å.

The modernization and computerization is done at Olis but can be done in the laboratory. The process involves disconnecting and discarding the original recorder and power supply assemblies. The chopper motor is replaced with a synchronous motor operated from the 60 Hz AC supply. A small stepping motor is coupled to the lead screw of the monochromator #1; this motor provides wavelength drive with 20 steps per nanometer. The toothed belts coupling the monochromator #1 lead screw to the indicator dials are replaced. A new power supply assembly for both lamps is connected to the optical unit. Finally, a photometer box containing the photo­current amplifier is placed near the PMT and is connected to the PMT via the original HV and signal leads coming from the PMT, and the computer is interfaced to the Olis hardware.

Among the Reasons People Ask Us to Modernize Their DW-2

The instrument produces the desired optical performance, notably for turbid samples such as solutions of soil, tissue, yeast, mitochondria, etc.

The hardware Olis adds includes the most simple, modern, and dependable electromechanical components, plus the newest Pentium computer, laser or color printer, and interface hardware. These new components require minimal maintenance and will extend the life of the optical bench's use for another decade or two.

The software we add is trouble-free. The polished Windows 2000/NT compatible software supports everything from setting wavelengths to fitting 3D results. The software can be used by all skill-level users and provides full control over the monochromators, supports spectral and kinetic data collection, data analysis, and data synthesis. If a facility is needed in the research or pedagogical environment, it will be found in this comprehensive software package. Some novel facilities in the software include:

• the proprietary method of successive integration for resolving polyexponential data which is five times faster than the Levenberg-Marquardt algorithm.
• the proprietary method of Matheson-DeSa for globally analyzing kinetic and equilib­rium data; this method employs Singular Value Decomposition, Downhill Simplex, and Matrix Exponentiation for extraordinary speed, precision, and power in analyzing data collected as a function of time, temperature, or concentration.
• OLIS software supports secondary devices, such as photon counting or laser firing.

Sample handling accessories can be computerized and controlled, too. If accessories are not available, but are needed, Olis offers a complete line for stopped-flow mixing, flash/laser photolysis, automatic titration, temperature ramping, etc.

Some Olis AMINCO™ Owners

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