High-Speed Capillary Electrophoresis (HSCE)

We introduced the use of ultra-thin wall, short separation capillaries for rapid separations and analysis

High-Speed Capillary Electrophoresis Using a Thin-Wall Fused-Silica Capillary Combined with Back-Scatter Interferometry

(Analytical Chemistry 2020, 92 (11), 7540-75646)

High-speed capillary electrophoresis (HSCE) is implemented using a 10 cm total length fused-silica capillary (50 mm i.d. by 80 mm o.d.) combined with refractive index (RI) detection using back-scatter interferometry (BSI). The short capillary length reduces analysis time while the ultra-thin wall (15 mm) efficiently dissipates heat from the separation channel, mitigating the deleterious effects of Joule heating. The separation capillary is mounted on a temperature-controlled heat sink that stabilizes temperature to ± 0.004 oC. This temperature stabilization improves separation efficiency and enhances RI detection. Ohm’s law plots confirm the superior heat dissipation of the HSCE capillary compared to a similarly prepared conventional CE capillary (50 mm i.d. by 363 mm o.d.). The speed and efficiency of HSCE combined with universal RI detection is illustrated through the separation of K+, Ba2+, Mg2+, Na+, Li+, and Tris+in approximately 30 s, with efficiencies greater than 500,000 plates/m. Run-to-run repeatability is explored using nine consecutive electrokinetic injections of a K+, Na+, and Li+ mixture. The average migration times and %RSD for K+, Na+, and Li+ were measured to be 22.04 s (1.59%), 26.81 s (1.38%), and 29.80 s (2.21%), respectively. Finally, we show that the BSI signal is sensitive to the separation voltage through the Kerr mechanism. This leads to peaks in the electropherogram from the injection process that are useful for precisely defining the start of each separation and quantifying the amount of sample injected onto the capillary.

Reduced Heating in Ultra-Thin Wall Capillary

Magnified view of a (A) HSCE capillary and (B) conventional CE capillary aligned side-by-side to help compare the relevant dimensions. To the right are Ohm’s Law plots measured for the (C) 10 cm long HSCE capillary and (D) a comparably mounted 10 cm long CE capillary. Both capillaries were filled with 20 mM imidazole BGE. The non-linear behavior in (D) denotes the onset of Joule heating while the curve in (C) remains linear.

Separation of 6 species in seconds

The HSCE separation of (a) K+, (b) Ba2+, (c) Mg2+, (d) Na+, (e) Li+, and (f) Tris+ at field strengths of (A) 270 V/cm and (B) 420 V/cm. The sample mixture was ~160 μM in each ion and separated in a BGE of 20 mM imidazole adjusted to pH 5.

Rapid and Repeatable Separation

Continuously recorded BSI signal during the repeated injection and separation of a ~330 μM mixture of K+, Na+, and Li+. The inset shows the peak assignments for the three ions, which were separated at 330 V/cm in a BGE of 5 mM imidazole adjusted to pH 5. Each separation starts with large positive going peaks associated with the electrokinetic injection process. A large negative going injection zone peak is also recorded following each separation. The injection durations were purposely varied for each separation.