Advances in Cutting and Cleaving of Fused Silica Capillary Tubing

Polyimide coated fused silica capillary tubing is frequently employed in a variety of analytical instrumentation. In this application note we revisit methods for cutting and cleaving capillary tubing with a focus on recent advances.

Fused silica capillary tubing's unique properties have made it a key component in separation scientist's tool box. Although used in analytical techniques such as GC, CE, capillary LC, CEC, and cytometry, it is of increasing importance in the area of fluid metering such as in drug delivery systems. Its dimensional precision is unmatched for microfluidic interfacing and mass flow control. The easy of cutting capillary to length is a key attribute, but care must be taken to insure that the appropriate cutting or cleaving method is selected so that optimum system performance is achieved.

Previous publications have outlined and defined the four primary methods of end face preparation, with those being standard cleaving, precision cleaving, laser cutting, and saw cutting (1,2). Subsequent work provided more detailed guidance on selecting the most optimum method (3). In this latter effort tubing attributes such as i.d., o.d. and wall thickness were considered, as were there influence on finished part length. A comparative analysis of end-face quality, perpendicularity, and cleanliness of the different techniques was also made. Advances in cutting and cleaving methods have been realized and are discussed in this note.

Recent Advances

Standard Cleaving — Cleaving capillary tubing to lengths less than 20 mm while maintaining a good end face had been challenging at the production level. Improvements in technique now allow standard cleaving to lengths as short as 5 mm on nearly all tubing products.

Precision Cleaving — This increasingly popular technique has seen similar reductions in finished part length due to tooling advances. Lengths as short as 15 mm are now achievable. This applies to tubing with a high glass cross sectional area such as our new 1/32" OD Capillary. Polymicro has also developed the ability to provide precision cleaved parts with up to 35 mm of the polyimide removed from the cleaved end. Previously, parts with this length of polyimide removed would have required a laser cut or lower quality standard cleave.

Saw Cutting — The maximum part length for saw cutting has increased from 4.5 cm to 12 cm due to investments in state of the art sawing equipment. New cleaning techniques allow for processing of tubing with i.d. down to 40 µm. As in the past, part length is limited when saw cutting small i.d. tubing. Likewise, the minimum o.d. that can be processed has been lowered. For short parts, the o.d. can be as low as 200 µm.

Laser Cutting — Industry leading attributes previously listed for laser cutting remain unchanged. However, related advances realized include improved control of end face contour of thick wall parts. Further, developments in the associated laser based polyimide removal techniques and equipment now allow for ablation of longer lengths of polyimide, i.e. up to 40 mm on most tubing products.

Table I summarizes the current guidelines for use in selecting the most appropriate cutting and cleaving method for your application.

Table I: Guidelines for use in comparing and selecting a cutting method for capillary tubing

Conclusion

This note reviewed recent advances in the primary techniques employed for cutting and cleaving capillary tubing. For assistance with your specific application please contact a Polymicro Technical Sales Specialist.

References

(1) "Cutting and Cleaving Capabilities", The Book on the Technologies of Polymicro, Polymicro Technologies Publication (2011), pp. 3–5.

(2) J. Macomber, R. Hintz, T. Ewing, and R. Acuna, LCGC Application Notebook, June 2005, p. 81.

(3) J. Macomber, P. Lui, and R. Acuna, LCGC Application Notebook, Sept. 2009, p. 66.

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