product review
Diode Array Detectors for HPLC High performance across the spectrum. James R. Riordon
T
he first diode array detectors (DADs) for HPLC were introduced in 1982. From the beginning, it was clear that these devices, which monitor absorbance across a broad UV–vis light spectrum, offered significant advantages over monochromators and variable wavelength detectors (VWDs), which concentrate on a single wavelength at a time. DADs, which are also known as photodiode arrays, initially lacked the sensitivity of the more mature VWDs; however, within a few years, rapid improvements in photodiode technology led to DADs that rivaled other detectors. As little as 10 years ago, says Donald Parriott of Pfizer, sensitivity, resolution, and other specifications varied significantly among different machines. Modern DADs typically exceed most analytical requirements and are suitable for the vast majority of applications. “It’s a pretty mature class of detectors,” he explains, with performance close to the theoretical limits of present-day optical systems and photodiodes. Today, most HPLC manufacturers offer DADs specifically tailored to their systems, with software that displays analyte peaks as a function of elution time and wavelength in an array of two- and three-dimensional
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product review
Table 1. Summary of selected DADs for HPLC. Model
HP 1100 Series DAD
168 Diode Array
PDA-100
170 DAD
20/20 DAD
L-7455
Manufacturer
Agilent Technologies 2850 Centerville Rd. Wilmington, DE 19808 800-227-9770
Beckman Coulter 4300 N. Harbor Blvd. P.O. Box 3100 Fullerton, CA 92834-3100 714-871-4848
Dionex 1228 Titan Way P.O. Box 3603 Sunnyvale, CA 94088-3603 408-737-0700
Gilson 3000 W. Beltline Highway P.O. Box 620027 Middleton, WI 53562 800-445-7661
Groton Technology 45 Discovery Way Acton, MA 01720 800-486-4786
Hitachi Instruments 3100 N. First St. San Jose, CA 95134 800-548-9001
URL
www.chem.agilent. com
www.beckmancoulter. com
www.dionex.com
www.gilson.com
www.grotontech.com
www.hii-hitachi.com
Wavelength range (nm)
190–950
190–600
190–800
190–700
190–700
190–800
Diodes
1024
512
1024
1024
512
512
Diode resolution (nm/diode)
0.7
0.8
0.6
0.5
1.0
0.1–0.2 nm (UV) to 5 nm (visible)
Optical slit width (nm)
1, 2, 4, 8, 16 programmable
4
1
1, 2, 4, 8, 16
1
1, 2, 4, 8, 16
Dispersion device
Grating
Grating
Grating
Grating
Grating
Prism
Spectral resolution (nm)
1
