Bare Fused Silica CE Capillaries and UV Transparency

All MICROSOLV capillary electrophoresis (CE) capillaries are manufactured from high‑purity fused silica, which is naturally UV‑transparent across a wide spectral range. This makes fused silica ideal for UV and UV‑Vis detection methods commonly used in CZE. 

However, in their functional form, CE capillaries are coated externally with polyimide, a durable polymer layer that protects the fragile glass during routine operation. Polyimide adds:

• Structural rigidity
• Mechanical strength
• Protection against flexing and handling stress
• Thermal and chemical durability

This coating ensures the capillary can be coiled, installed, and used repeatedly without breaking.

Why Polyimide Is Not UV‑Transparent

Despite its mechanical advantages, polyimide is not UV-transparent. When light from the detector passes through a polyimide-coated section, the polymer absorbs and blocks UV wavelengths, preventing accurate and reproducible detection.

For this reason, CE systems require a UV‑transparent window positioned at the detector’s optical path.

Creating a UV‑Transparent Detection Window

Even though the full capillary is coated in polyimide, this does not interfere with UV‑based detection, because only a small section needs to be cleared of the coating.

To achieve this, users can employ the MICROSOLV Window Maker™, which precisely burns away the polyimide without damaging the underlying fused silica. This creates a clean and reliable UV‑transparent window suitable for:

• UV detection
• UV‑Vis detection
• Fluorescence detection requiring a clear optical path

The remainder of the capillary stays coated for structural strength, while the exposed region provides a clean, optically accessible point for detection.

Ordering Information:

Click HERE for capillaries for CE ordering information and pictures.