Finding alternatives for Self-pack columns

Many of our customers are used to use the New Objective PicoFrit or SilicaTip emitters to pack their own “integrated-tip” nanoLC columns. However, since these emitters have been hard to get recently, some rethinking and alternatives are dearly needed.

Self-Pack columns with integrated emitters (also known as pulled emitters) are fused silica lines often with an Outer Diameter (OD) of 360µm, an Inner Diameter (ID) of 50-100µm (depending on the flow rate), and a pulled tip between 8 and 30µm ID. In the case of the PicoFrit, a frit is packed in the pulled tip (as shown in figure 1).

There are great benefits in using integrated tip capillary columns, the main benefit being the packed bed is reaching all the way to the point of ionisation and the lack of any dead volume, avoiding any peak broadening. The width of the tip seems to be an almost religious decision but definitely is a robustness issue as well. The smaller tips (8µm), the higher the risk of blockage in pulled emitters without a frit mounted, whereas the wider tips (15µm) are more forgiving.

The Work-around

However, as mentioned before, due to the fact that the widely used New Objective emitters are hard (if not impossible) to get recently, some rethinking is needed. And we, at MS Wil, are here to assist you in this process.

In our view there are a few options to consider when one has no other choice than to use the integrated emitter style columns:

1. Make your own pulled emitters, from a suitable fused silica tube with the use of a Sutter Laser-Based Micropipette Puller P-2000. One could even consider fritting these pulled emitters (protocol), then packing the emitter with a column packing device.
2. Use prepacked integrated emitter style columns.

The Alternative

The alternative is to look at separated column/emitter set-ups, which have many advantages and, when chosen well, are competitive with the integrated emitter set-ups. Of course, a separated set-up will cause a minor dead-volume post column, as a separate emitter needs to be used. Still the volume of a 10µm ID cylindrical emitter of 4cm is only 0.1nl, which has a negligible effect on peak width.

Should you be open to make this change the following options could be considered:

1. Make your own columns by fritting a suitable fused silica tube and pack them using a column packing device.
2. Connect a suitable emitter using a zero-dead-volume union, which might consist of fused silica or metal. The metal versions and some fused silica ones are tapered, meaning the end of the tip is sharpened by polishing the surface at an angle. Alternatively pulled emitters are available in short versions (7-10 cm).
3. Connect a suitable emitter that has an integrated liquid junction, mount it into a sprayer that functions as a positioning device, zero dead volume, and connection point for the High Voltage (HV) connection. Columns can be connected using a 1/16” Viper^®-like connector. Connectors can be mounted on self-packed columns, allowing for great ease of use!

One point that needs to be mentioned is about the coated emitters, which some large MS vendors teach their users to operate, as their sources have an HV-connection point at the end of a column rail. As these emitters have a limited supply when I’m writing this tech note, it will be important to look into an alternative way to make an HV connection. Coated emitters are a great way to use the HV-point at the end of these well-spread ion sources, however, the coating dissolves over time due to hydrolysation of the metal over time. Which is a good reason to look into an alternative connection (as described above), if only for robustness of your installation. A final word on this, the connection point was originally designed for metal needles…

The practical bit

As a solution provider in the field of proteomics MS Wil works with a wide range of suppliers who, together, can provide alternative solutions to keep you going:

Fritting and Packing your own columns
Should you be interested in packing your own columns we have started working with Next Advance. Nowadays Next Advance produces a range of products for Life Science laboratories but started as a column packer company. Next Advance supplies us with a variety of column packers (with and without integrated stirrer), a Frit-Kit to create Kasil Frits, and fused silica tubing. Another supplier of fused silica tubing in our portfolio is Trajan. To pack the columns we supply Dr. Maisch media.

Pre-Packed columns
For Integrated emitters, pre-packed columns are supplied by CoAnn Technologies and by IonOpticks. CoAnn is founded by a team of professionals who used to work at Pacific Northwest National Laboratory and still based in Richland WA, USA. CoAnn provides a large list of column options in both Top-Down and Bottom-up applications, with and without fitted connectors for ease of use. IonOpticks is a company based in Australia, consisting of a team of experts in a broad array of LC-MS platform technologies, with their goal to produce high-performance nanoflow chromatography solutions for the global research community.

For separated columns we also offer solutions from CoAnn, but also from the brand PepSep, which is currently part of Bruker. PepSep produces a wide range of custom, separated columns with and without connectors. Later in this text they will return for their work on emitter and sprayer development.

Suitable emitters
Concerning the emitter, both PepSep and CoAnn return to the stage. In order to find an alternate supplier for New Objective SilicaTip emitters we started supplying pulled emitter Tips by CoAnn. CoAnn make a range of Tips, ranging from 10-100µm ID with a Tip ID between 5-30µm pulled from 360µm OD fused silica tubing.

PepSep provides an interesting range of novel developments to the commercially available range of emitters. Even though PepSep has been making 150µm OD fused silica and metal emitters for a long time, with ID’s of 10 and 20µm for fused silica and 30µm for the metal tips for general use. The company also developed emitters with integrated liquid junctions, which fit in sprayers that can be mounted on the Thermo Nanospray Flex™ Series and EASY-Spray™ model Ion Sources. These new emitter/sprayer combination products allow for easy-to-use and very robust nano ESI set-ups, easily connecting columns (or transfer lines) using a 1/16” Viper^®-like connector.

Dotting the i’s and crossing the t’s
When putting together your own column/emitter set-up it is important to use suitable connectors. In order to allow you to easily make the connections you need to make, we work with the VICI line of low-volume unions, 1/32”, 1/16”, and 360µm connectors. These connectors may be used just to connect two lines, but are often used as the basis for zero dead-volume liquid junctions.

To mount these liquid junctions and safely connect the High Voltage (HV) power supply, Phoenix S&T provides isolating holders with magnetic HV connection line connectors that may be mounted on the Thermo Nanospray Flex™ column rail. Phoenix S&T is also a supplier of a range of column ovens for nano-LC.

Finally, if you are developing your own columns and you’re cutting emitters, it is important to make a clean cut and make that cut as smooth as possible. Cut fused silica often still has small pieces of glass attached to the end, which, if they break, may cause a blocked emitter. In order to always be sure your fused silica cuts are perfectly smooth, ESI Solutions developed their capillary polishing station, which is a device suitable to (as the name states) polish the ends of your fused silica capillaries, ready to endure many injections without unwanted dead volumes or a blocked emitter.

Product Numbers & Specifications:

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