The Olis DM 45 spectrofluorimeter uses research quality optics and a high intensity steady-state 75 or 150 watt xenon arc lamp with outstandingly flexible and useful computer control. The Varian Eclipse is quite a bit lower in quality, using lesser optics, a pulsed xenon arc lamp, and ‘appliance-specific’ software.
Varian identifies the monochromators in the Eclipse as being a “Monk-Gillieson” type. Do you know what this is? We didn’t. So, we looked it up and learned “For low-resolution applications, the Monk-Gillieson mount enjoys a certain amount of popularity, since it represents the simplest and least expensive spectrometric system imaginable.”1
While this Monk-Gillieson monochromator is handsomely displayed on the Eclipse brochure, seeing it is as worrisome as reading about it: there are many components which will fail in time. Compare this with the single 45 x 40 mm grating inside of an Olis DM 45 monochromator which moves with a computer controlled mini-sine bar assembly and the 40 mm square mirror cemented into a fixed position. Our optical bench has a much higher likelihood of reliable performance for the decades ahead.
The reason Varian gives for using the pulse lamp is to avoid photobleaching.
Of course, photobleaching of one’s sample can be minimized by
- manual slit closure between measurements,
- removal of sample from compartment between measurements,
- moving the monochromator to a wavelength which does not photolyze the sample between measurements,
- turning the lamp off between measurements, or
- computerized shutter closure between measurements
Options (1), (2), and (3) are free and easy. (4) is not recommended, since repeated lightings will shorten the life of the lamp, and (5) adds to the price.
They mention that a pulse lamp is a “long-lived excitation source.” We find that steady-state 75 watt xenon arc lamps last approximately 1000 hours, with some becoming too noisy for the given application at 500 hours and others lasting well into the thousands of hours, depending upon the lamp itself, the number of time it is lit, the amperage run through the lamp, and the acceptable noise level. (We have not found an indication of how long a pulse lamp is rated to last, so let us know if you know!)
One could successfully argue that the actual reason for using a pulse lamp is that the Monk-Gillieson optics are so insensitive that a steady-state source could not be used successfully.
They specify: “A newly designed reference signal system has been added to provide users with much more control over signal dynamics.”
We point out: The only way a pulsed source fluorimeter can be trusted is if a reference channel is used, since the variability in intensity between flashes can be very significant.
Along this line, they refer to “corrected spectra.” They are correcting their results against the lamp intensity, but they are not making an absolute correction in the text book sense.
For data collection modes, our competition refers to “excitation, emission, constant wavelength synchronous, and constant energy synchronous spectral scanning,” which means that one can scan excitation, or scan emission, or scan the two monochromators in lock-step with a fixed number of nanometers between them, or scan the two monochromators with a fixed number of wave-numbers between them. Olis offers three of the four options and the last being the one we don’t yet have since no one has asked about this feature to enable the energy difference between the monochromators to remain constant.
The Eclipse is designed to be a simple application device which will be replaced in 2-5 years.
The Olis DM 45, like all Olis instruments, is designed to be modular—easily optimized for speed or sensitivity; easily accessorized with Olis or other sample handling accessories; easily enhanced to support flash photolysis and other high speed applications—and to last decades.
The points against the Olis DM 45 are that we do not offer a multiplate reader and our modular design has a larger footprint. Our price is higher, too, of course. But, as someone with 15+ years experience with an Olis noted in late 2002, “You guys make investment spectrophotometers!” That is, like other Olis equipment, the Olis DM 45 spectrofluorimeter is not a throwaway appliance but a research caliber system which will provide years of reliable use.