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Make near perfect glass capillary ends, using the Capillary Polishing Station

Make near perfect glass capillary ends, using the Capillary Polishing Station

Looking for a way to make near perfect glass capillary ends in the lab, to give optimal chromatographic response and robustness? The new and improved Capillary Polishing Station 2 (CPS-2) from ESI Source Solutions allows you to do so. This device provides a simple means to make clean polished ends on various OD glass capillaries tubing and 1/16” PEEK tubing as well. This is essential for reliable high-sensitivity capillary chromatography. The device consists of two parts, the polishing base and the capillary jig, shown below (see figure 1).

Figure 1. Capillary Polishing Station Package (incl. polishing base, capillary jig, and guide sleeves)

The new Capillary Polishing Station has three disks of lapping film, a 30 µm aluminum oxide disk (green), a 15 µm diamond disk (orange) and 1 µm diamond disk (purple or white), which are located in the approximate locations shown in the picture above (figure 1). Guide sleeves for different OD glass capillary tubing are also included, one for 360 µm and one for 280 µm tubing.

Imaging the ends of the glass capillaries is critical to the polishing process. We highly recommend the use of ESI’s Digital Imaging Station (DIS, see figure 2), as it has all the bits needed to inspect your work and display the images on a PC (not included) without the fuss of optical microscopy. All images of capillaries in this blogpost are made using the DIS.

Figure 2. Digital Imaging Station (DIS)

How to polish a piece of glass capillary tubing using the Capillary Polishing Station:

1. The glass capillary should be either dry, flushed free of organic liquids or contain only an aqueous solution.

2. Cut the glass capillary to length and examine cut under magnification. The most effective cut can be made by scoring the glass lightly with a diamond scribe and pulling straight apart lengthwise. Inspect the cut end under + 20x magnification (as shown in figure 3 below). If the end cut is very jagged, recut to obtain a fairly flat end before polishing.

Figure 3. Two hand cuts (that are fine for polishing).

Take some time to practice and be able to make hand cuts like this. And note that polishing ragged glass ends will damage the polishing media.

3. Select a guide sleeve for the capillary jig which is as close as possible to the outer diameter of the glass capillary tubing you are polishing. One PEEK sleeve for ~ 360um OD tubing is included, it is easy to cut 1/16” PEEK tubing of any size to match your needs.

4. Place the capillary jig on the Capillary Polishing Station over the green disk. This one is higher than the others and will afford clearance to the position of the guide sleeve.

5. Insert the guide sleeve into the capillary jig from the top (see figure 4) until it meets the level of the green disk. If needed, secure the guide sleeve in this position using the tan PEEK collars.

Figure 4. Guide sleeve inserted into the capillary jig (setp 5, left), and guide sleeves (right).

6. Put a little water onto the diamond lapping film disks (orange and white) ONLY! The green disk is for polishing PEEK tubing and should only be used dry.

7. Place the capillary jig over the orange lapping film disk (15 um) with the guide sleeve in the water.

8. Insert the glass capillary into the guide sleeve, allowing the glass capillary to contact the surface, holding it there with one hand in contact with the lapping film disk. Apply only enough pressure to keep the capillary in contact with the lapping film while polishing.

9. Using the other hand, polish the capillary by moving the jig in a gentle circular motion for a couple of seconds on the orange lapping film disk (see figure 5). Pull the capillary up slightly and move to the white lapping film disk (1 um) and repeat to finish the polishing process.

Figure 5. Polishing of the capillary on the orange disk (step 9).

10. Remove the capillary from the capillary jig.

11. Wipe off the polished end with a wet Kimwipe.

12. Examine the capillary under magnification. Repeat step 5 if needed, moving to the white film disk to finish the polishing process.

13. Using a pressure vessel or syringe with capillary fittings, flush the glass capillary tubing clean using methanol. Be sure to flush away from any integral frit. Sonication may be helpful to remove all polishing debris from inside the glass capillary.

14. When finished with polishing (see figure 6), rinse the lapping films with water to remove debris, dry with a Kimwipe or let air dry.

To polish 1/16” PEEK tubing using the Capillary Polishing Station, remove the capillary guide sleeves and insert the tubing to be polished directly into the open hole on the capillary jig.

Polish the end until flat and smooth on the Dry Green lapping film disk, finishing on the other disks as needed.

Capillary Polishing Station (5)
Figure 6. Two examples of finished polished capillaries. (With practice it is easy to make high quality finished ends like this.)

When wear or damage is observed, the lapping film should be replaced. Use a fingernail or plastic spatula to gently pull the film out of the polishing base, replacing it with a new disk. Be sure all adhesive from the previous disk is removed; a squirt of methanol will help. As the new disk is being installed, smoothen out the air pockets with your finger while applying it to surface.

Replacement polishing media is available from us in 15 packs of disks (5 each grit) in either diamond (as supplied with unit) or aluminum oxide media. Some customers have a preference to one or the other (the aluminum oxide is less expensive…), but both produce high quality finished capillary ends in the hands of experienced users.


Product Numbers & Specifications:

SupplierProduct Nr.Specifications
ESI Source Solutions (ESS)CPS2Capillary Polishing Station
CDP-A2Replacement Polishing Disks – Aluminium Oxide Media (5 pieces 30µm, 12 µm, and 1µm per 15 pack)
CDP-D2Replacement Polishing Disks – Diamond Media (5 pieces 30µm, 12 µm, and 1µm per 15 pack)


Any further questions or comments? Please don’t hesitate to contact us by mail (sales@mswil.com).

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