“Capillary electrophoresis (CE) was born of the marriage of the powerful separation mechanisms of electrophoresis with the instrumentation and automation concepts of chromatography.”⁴ CE is a separation method based on the differential migration rates of sample components within a capillary when an electrical field is applied axially to that capillary. The detection of sample components is usually “on-column” using UV spectrometric or fluorescence analysis through a “window” in the capillary. CE has become a powerful technique, finding a wide range of applications areas, including the analysis of proteins, peptides, chiral compounds, pharmaceuticals, inorganic ions, and DNA to mention a few. CE played a pivotal role in the Human Genome Project’s ultimate goal of unraveling the sequence of human DNA. It is the primary workhorse in sequencing facilities and DNA forensic laboratories worldwide.

Performing electrophoresis in small-diameter polyimide coated capillary allows the use of very high electric fields, and the efficient dissipation of the Joule heating that results. High electric field strengths produce very efficient separations while minimizing separation times. Key features that make fused silica capillary tubing the column material of choice in CE include:

• The surface ionization characteristics of fused silica when in an applied electrical field generates electroendomosis, also known as Electrosmotic Flow, or EOF. This basic pumping action drives most CE applications and is responsible for the techniques high chromatographic efficiencies.

• Capillary tubing has a high dielectric strength, giving ample isolation for the high voltages (up to 30kV) used in CE.

• The polyimide coating can be easily removed in a process called “windowing”. Windowed capillary has high transmission in the UV-Vis spectral region, allowing for direct on-column absorbance measurements.

• Windowed capillary exhibits low background fluorescence, making it ideal for fluorescent detection schemes, including LIF (Laser Induced Fluorescence).

• Capillary can be easily rinsed and filled with solutions and buffers by either positive pressure or vacuum.

• Modification of capillary surfaces through dynamic coatings, covalently bonded phases, or stabilized gels, allow for control of EOF and can impart unique separation mechanisms.

• The durability and abrasion resistance of polyimide coated capillary allow for great flexibility in instrumental design and hyphenation interfacing.

• Capillary can be easily cleaved to length, providing users great latitude in adjusting column length and economies of scale in tubing procurement.

CE has carved out a unique niche in the analytical laboratory, both as a fundamental separation tool and a complementary technique to established methodologies. Polymicro continues to be the primary supplier of tubing to this market, providing capillary ranging in ID from 2mm to 150mm. Polymicro set the standard in outside diameters (OD) by introduction of the 375mm and 150mm TSP product lines, and offers capillary for CE in a variety of formats including: bulk capillary on spools, capillary cut to prescribed lengths, windowed capillary, capillary assemblies, and custom capillary arrays. A number of CE manufacturers turn to Polymicro for custom sizes to meet their specific instrumental design, and rely on Polymicro’s expertise for design and development assistance.

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