Best Practices: Making Connections
This instruction provides basic information on connecting standard-length 5 cm distal or standard coated PicoTips® to a transfer line or capillary column. "PicoTip" refers to any of New Objective's high-quality tips for electrospray ionization, such as SilicaTips™, PicoFrits®, and TaperTips™.
NOTE: Users must take care when tightening the MicroTight® fittings, making sure to only tighten enough to prevent leaks from occurring. Due to the delicate nature of some fused-silica tubing, it is possible to damage the tubing if the fittings are overtightened.
- If the union is assembled, unscrew and remove the compression fittings from both ends of the union.
- Screw the white gauge plug finger-tight on to one end of the union. Thread the fused-silica transfer line through a green MicroTight sleeve. The appropriate sleeve size is 0.002-0.003 inches greater than the OD of the capillary tubing. Use the green MicroTight sleeves with 360 µm OD tubing. After the transfer line passes through a green sleeve, thread it through one of the compression fittings. Figure 2 shows the union loaded with the white gauge plug on the right and fused-silica tubing threaded through a tubing sleeve and a compression fitting. Cleave the end of the tubing and slip it into the union until both the tubing and the sleeve ends seat against the gauge plug inside the union. Screw the compression fitting finger-tight into the union, as shown in Figure 3.
- Remove the gauge plug.
- Carefully trim a new green MicroTight sleeve to a length of approximately 14 mm. The shorter sleeve will allow the coating on the PicoTip to contact the conductive elastomer inside the CTM.
- Choose a your PicoTip emitter. As no voltage is being applied to this fitting, an uncoated (N) PicoTip should be used.
- Insert the back, or distal, end of the PicoTip through the trimmed sleeve and through the other compression fitting. When properly installed, the tip end should extend 15-20 mm past the end of the fitting when it is tight. This will afford optimal positioning of the PicoTip within the adjustment range of the stage plate. Using a ruler, measure and note the distance the tip extends from the fitting. Remove the fitting/sleeve/PicoTip assembly and carefully trim the back end of the PicoTip so the extension of the tip beyond the fitting is 15-20 mm. Cleave the remaining portion from the back end of the PicoTip.
- After trimming, reinsert the assembly into the union, seat the PicoTip and sleeve against the transfer line or column tubing, and tighten the compression fitting finger-tight. Pull gently on the tubing to ensure the connection is tight. Figure 6 depicts the fully assembled union.
CAUTION: Always use chemical- and puncture-resistant gloves and ASNI-approved safety glasses when handling fused-silica tubing.
Insert tubing approximately half-way through union
Repeat for the opposite side; butt tubing ends together
Tighten primary ferrules, alternating each side until core clarity improves
Tighten scondary ferrules
Plumbing the PicoClear Union with 360 µm OD Fused-Silica Tubing
- Gently push 360 µm OD fused silica tubing through a primary/secondary ferrule pair into the union until the end of fused silica is positioned approximately halfway through the clear insert (Figure 1)
- Repeat for the opposite side of the union, gently pushing the second piece of tubing into the clear insert until it butts against the first piece of tubing. There should be no visible gaps between the two ends (Figure 2).
- The junction between the two pieces of tubing should be positioned within the center of the clear insert.
Note: It is not necessary for the tubing junction to be at the exact center of the clear insert. A leak tight seal can be obtained even when the tubing junction is slightly off-center.
- Tighten each primary sealing ferrule ¼ of a turn, alternating between each side (Figure 3).
Note: Successful plumbing requires that the tightening of the primary nuts be done in a balanced manner,
- Discontinue tightening when a visible gap at the tubing junction can not be seen and the insert becomes optically clear (Figure 3).
- Tighten each secondary locking ferrule ½ to 2 revolutions to secure the tubing (Figure 4).
Supplying High Voltage
- The MicroTee joins the transfer line to the PicoTip and supplies the high voltage. Orient the MicroTee as shown in Figure 7 so that the platinum electrode is facing away from the user and the setscrews are visible. Unscrew the nuts and remove the black MicroFerrules from the posts of the MicroTee.
WARNING: Do not loosen the setscrews or remove the electrode cap, as this may damage the electrode. The solvent will not become charged and an electrospray will not form.
- Thread the end of the PicoTip tubing through a green MicroTight sleeve, which is used for assembly with 360 µm OD tubing. Make sure the PicoTip does not extend past the tubing sleeve end that will be inserted into the MicroTee. Thread the sleeved PicoTip through the fitting nut and a black MicroFerrule, as shown in Figure 8.
- Cleave the end of the PicoTip after the tubing is threaded through the sleeve, nut, and ferrule. (Refer to Tech Note FS-1 for cleaving technique.) Slip the end of the tubing through the right post of the MicroTee, as viewed in Figure 9A, until the tubing and sleeve seat against the bottom ledge inside the post, as shown in Figure 9B. Screw the nut finger-tight onto the MicroTee.
- Insert the distal end of the fused-silica transfer line through a green MicroTight sleeve, then through the nut and the black MicroFerrule, as shown in Figure 10A. Carefully trim the end of the transfer line. After trimming, insert the assembly back into the MicroTee, seat the transfer line, ferrule, and sleeve against the PicoTip, and finger-tighten the nut, as shown in Figure 10B. Gently pull on the tubing ends to ensure the connection is tight. Check for leaks by running solvent through the tubing at the expected operating pressure. Leaks will be apparent if solvent collects at the exposed ends of the sleeves.
NOTE: This option is not recommended with PicoFrit columns.
- Orient the ZDV union as shown in Figure 11 so that the "T" bracket is facing away from the user. Unscrew the nuts and remove the ferrules from the union.
- Insert a green SealTight sleeve through the ferrule and nut. Thread a PicoTip through the sleeve/ferrule/nut assembly, as shown in Figure 12A. Cleave the end of the PicoTip after the tubing is threaded through the sleeve, ferrule, and nut.
- Slip the end of the tubing into the right side of the union until the ferrule and sleeve seat against the bottom ledge inside the union (Figure 12B). Screw the nut finger-tight into the union. Do not tighten enough to compress the sleeve.
NOTE: Be careful not to touch the tip to any surface.
- Trim 5 mm from the end of a green SealTight sleeve and insert the sleeve through the ferrule and nut. Thread the back end of the fused-silica transfer line through the sleeve/ferrule/nut assembly. Cleave the back end of the transfer line and slip it into the left side of the union until the transfer line/ferrule/sleeve assembly seats against the PicoTip. Tighten the nuts on both ends of the union. Pull gently on the tubing to ensure the connections are tight. Figure 13 depicts a fully assembled ZDV union.
Proper cleaving of fused-silica tubing is a critical but often overlooked operation in the preparation of emitters and columns prior to use. A flat, smooth cleave is essential for maintaining low dead volume connections with other sections of fused-silica tubing. It is also critical that cleaving does not generate flow-stopping particulate matter. Cleaving is best accomplished with a high-quality diamond chip or sapphire cleaving tool.
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