Product Review
CD begins
to bloom Circular dichroism adapts itself to the pharmaceutical market and finally blossoms.
F
or many years, circular dichroism (CD) has had a small but devoted market focused on the conformational analysis of proteins and other biopolymers, and augmented by more basic studies of chiral molecules. Allhough biopolymers remain a major application with potential for continued growth, the market for chiral analysis is expanding even faster. Several sources interviewed for this article agree
Elizabeth Zubritsky
representative commercial instruments and accessories for CD (Table 1) and VCD (Table 2). This review is not meant to be eomprehensive. Readers should contact companies directly for details. that the need to study stereospecific interECD instruments actions of molecules and to develop and In a conventional CD instrument—also produce enantiomerically pure drugs is called an "electronic" CD (ECD) instruincreasing the demand for chiral discrimiment—the light from a xenon lamp passes nation as a research and validation tool. through a monochromator, which selects Thus, chiral discrimination is being applied the measurement wavelength. Then the to more molecules, and it is moving bebeam goes through a polarizer and a phoyond the realm of biochemistry departtoelastic modulator, which switches the ments and medical schools. beam between left- and right-circular polarization. Finally, it passes through a cuvette At the same time, chiral testing is rethat contains the sample, and the resulting ceiving more attention from regulatory signal is received by a photomultiplier. agencies, such as the U.S. Food and Drug Administration (FDA). Some researchers, Several variations on this theme including Neil Purdie at Oklahoma State available. Some vendors use a double University, are even developing CD-based prism-based monochromator but others quality-control assays. Such trends are endouble-grating or prism-grating monocouraging interest in CD and its infrared chromators Some vendors purchase their counterpart, vibrational CD (VCD), and photoelastic modulators from Hinds Instruleading companies to launch new standments but others make their own In addialone instruments and delve into the realm tion a few inetnimentc are rtaceH nn earlier of CD detectors for chromatography. instruments old Cary or Aminro models d 'a To help readers understand this growing forexamnle but most are marketplace, Analytical Chemistry reports onHowever, the biggest difference among Analytical Chemistry News & Features, August 1, 1999 5 4 5 A
Product
Review
Table 1 : Summary of selected circular dichroism instruments. Model
PiStar-180
202
MOS-420
Manufacturer
Applied Photophysics 203/205 Kingston Rd. Leatherhead Surrey KT22 7PB U.K. +44 1372 386537
Aviv 750 Vassar Ave. Lakewood, NJ 08701 732-367-1663
Bio-Logic1 1, rue de L'Europe F-38640 Claix-Grenoble France +33 476 98 68 31
URL
www.apltd.co.uk
www.avivinst.com
www.bio-logic.fr
Dimensions W x D x H (ft)
- 3 . 6 x 1.7x 2
—4.6 x 2 x 5
-3x3x 3
Measurement modes
CD, absorbance, fluorescence. FDCD; optional: fluorescence polarization, fluorescence emission scanning, photodiode array absorbance scanning
CD, absorbance; optional: fluorescence, FDCD
CD, absorbance, fluorescence, fluorescence polarization, LD
Usable spectral range (nm)
^80—900
165-900; optional: up to 1100
185-800
Wavelength accuracy (nm)
±0.5 (180-900 nm)
±0.2 (165-300 nm); otherwise, ±0.3 or greater
±0.2
Detection range (mdeg)
±1000
1-5000
±1000
Baseline stability
