product review
Capillary Electrophoresis: Finding a Niche Where HPLC struggles, CE thrives. Laura DeFrancesco
I
nterest in capillary electrophoresis (CE) has waxed and waned in the decade since the first commercial instrument was introduced. Now, CE seems to be establishing itself as the technique of choice for certain applications. For example, according to company representatives and experts, CE provides chiral analysis at a lower cost and is better than HPLC at separating highly charged and polar species. CE’s facility for small ion analysis has made it a mainstay in the food and beverage industries. And biotech companies have started to incorporate CE their research as well as into QA and QC. DNA sequencers using CE also played a major role in sequencing the human genome. When last reviewed in these pages in 1996, the commercial CE field had narrowed to a handful of companies. (Dedicated DNA sequencing instruments were recently reviewed and are not included in this discussion [1].) Since that time, the field has narrowed even further to just a few companies, with two giants, Beckman Coulter and Agilent Technologies, becoming the dominant players. Table 1 lists representative features of CE instruments from five companies. Readers interested in these products should contact the companies for a complete list of features.
A short history As with most new technologies, CE was initially fraught with technical difficulties. Barry Karger, director of the Barnett Institute at Northeastern Universi-
ty, likens it to the early days of LC. In the beginning, he says, “[LC] was horrible. Every column was different. It was many years before the technique became robust.” However, some of the problem may have been the users who first bought the instruments. “Chromatographers tried to [use CE] and did not fully recognize that it was electrophoresis. And CE was governed by those rules, not chromatographic ones,” says David Heiger of Agilent. “For those who
know electrophoresis, you have a much easier entrance.” Although the chromatography problem still exists, Jeff Chapman of Beckman Coulter says that the adoption of “CE thinking” has been key to the technique’s success. Instead of migration or retention times, which are chromatographic descriptors, CE focuses on mobility. “The use and development of mobility has changed the face of how we operate,” claims Chapman. “It took CE from what was perceived as not re-
S E P T E M B E R 1 , 2 0 0 1 / A N A LY T I C A L C H E M I S T R Y
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product review
Table 1. Selected Features of CE Systems. Model
Capillary Electrophoresis System
P/ACETM MDQ Methods Development System
PrinCE
MCE 2000
Ultra-Plus II CE
Company
Agilent Technologies 2850 Centerville Rd. Wilmington, DE 19808 800-227-9770 www.agilent.com/chem
Beckman Coulter, Inc. 4300 N. Harbor Blvd. P.O. Box 3100 Fullerton, CA 92834-3100 714-871-4848 www.beckmancoulter.com/
Prince Technologies P.O. Box 2194 7801 CD Emmen The Netherlands 31 (0)591 629184 www.princetechnologies.com
CombiSep 1915 Scholl Road Applied Science Building II Ames, Iowa 50011 515-294-2837 www.combisep.com
Micro-Tech Scientific 140 South Wolfe Rd. Sunnyvale, CA 94086 408-730-8324 www.microlc.com
Approximate price (USD)
$49,000 with ChemStation, PC, and printer
$60,000
$23,000–32,500 (including UV–vis and software) depending on exchange rate
Price based on options
$9500–65,000
Pressure, vacuum, or electrokinetic
Pressure (between –180 and Vacuum and electrokinetic High pressure, time con+250 mbar), electrokinetic trolled injection valve, hydrodynamic, and electrokinetic
Injection mode Pressure, vacuum, or electrokinetic Capillaries Minimum length
8.5 cm (from injection point 7 cm (from injection to Flexible in length and to detector); 33 cm total; detector); 27 cm total; diameter 25-, 50-, 75-, or 100-µm maximum length is variable standard i.d.
Compatibility 25-, 50-, 75-µm extended All commercially available pathlength; high-sensitivity capillary dimensions cell (75 µm) Power supply Voltage range ±30 kV Current 0–300 µA Power 0–6 W
±30 kV 0–300 µA 0–9 W
±30 kv –200 to 200 µA 0–6 W
40 cm total; 20 cm effective 5–50 cm length; 75-µm i.d.
Standard; 96 capillaries in linear array format
50, 75, 100, 250, and 320 µm i.d.; open or packed capillary
±20 kv 0–4.0 mA total current
±60 kV 1.2 mA Time programmable voltage control
Sampling
Thermostatted 48-position carousel; 100-µL to 2-mL vials
Thermostatted autosampler; 2-mL and PCR vials; 0.5-mL tubes and 100-µL tubes; 96-well plates
4-position or 30/48 position 96-well format PCR plates, autosampler; variable vial 0.2 µL to 1.0 mL volume sizes well plates
96 and 384 well plates, 2 mL vials
Detectors
UV–vis diode array
Modular UV–vis diode array, selectable wavelength UV–vis
Allows use of any CE compa- UV at 214 nm standard; tible detector, including MS, 254, 280, and 305 nm also fluorescence, LIF, conductivi- available ty, UV–vis, photodiode array
UV–vis, MS
Features
High-sensitivity pathlength capillaries; self-aligning capillary cartridges; high pressure at both ends for CEC; ChemStation software; automated fraction collection; integrated CE/MS (quadrupole and ion trap mass spectrometers)
Automated fraction collection; high pressure at both ends for CEC; recirculating liquid temperature control; independent buffer and sample temperature control; mobility plots; Ceaser algorithm for quanititation; 32 K software (combined platform for LC/CE); large array of chemistry kits and reagents
Fully modular; high pressure 96 simultaneous separaat inlet, outlet or both ends tions; software processes for CEC; easy-to-couple to 96 samples in
