Often our customers ask us: “How do I make my connections work in my nanoLC-MS set-up?” or a variant of this phrase. In this article we will provide you with our insight into this misty territory, with many options and pitfalls.
The first question for you to answer is: “What do I want to connect and with what purpose”. Is it “just” a coupling between a transfer line and a column or emitter, or do you want to turn the connection into a Liquid Junction at the same time. In latter case, you may wish to look into some electrical safety features at the same time.
Frequently made nLC Connections
Some connections are made more than others, most nLC connections are straight through and some make use of a T-piece (T’s) or cross. T’s and Crosses are used to make Liquid Junctions, using gold or platinum electrodes/wires, but T’s may also be used to facilitate vented trap-LC set-up’s. At the end of the day the fittings used are of limited specification, but whatever you combine, things do have to fit! Below (in figure 1) we provide an overview of examples of connections you may find being used:
Frequently used and Novel nLC Connections
Over the years a lot has stayed the same in nanoLC-land, mainly due to the resistance to change in the realms of the larger vendors. nLC connections offered today have to be stable over a 10 year plus period. Even though they say “never to change a winning team”, developments do not stop and often may improve the finicky way nLC connections are made. In making tight connections it’s all about dimensions.
Let’s start with some well used Outer Diameter (OD) dimensions:
Fused Silica tubing:
1/16″ of 1/32″
360-365µm (widely used) or 280µm (UltiMate™ 3000 RSLCnano System)
150µm or 360µm
2) Nuts and Bolds
Secondly, there are a number of different connectors that ensure a zero dead volume connection. Some examples are:
As you can see there is a wide range of products available to make nLC connections work, however, some work better than others. Ten years ago one had no choice but to use sleeves, today there are a number of options that will allow for easy leak tight connections on 360µm OD Fused Silica lines.
The unions and crosses themselves also come in different variants:
Unions are made to ensure a “Zero Dead Volume” nLC connection. One note here, to add to the confusion, “zero dead volume” does not mean that there is no volume between the two ends you are connecting. It means that there is no void volume between the ends. Many ZDV-connectors have a bore in the metal divider between the lines, if the hole in the divider is similar to the inner diameter of the tubing you are connecting, then the volume in the divider is not considered “dead volume”.
The rational is that as the inner diameter of the continuous line (tube 1 – union – tube 2) is not expanded, and therefore doesn’t affect the flow, the hole is counted as part of the flow line. Dead volume, that causes your chromatography peaks to broaden, is a larger volume in which the laminar flow is disturbed. An extreme example of this are the UV-detector cells that used to be placed in-line with a Mass Spectrometer. Having said that, also poorly made fittings cause dead volume and they are the main cause for dead volume in a nanoLC system, so be careful when making your own.
Part Numbers & Product Specifications:
|VICI 360µm FS Connector – PEEK
|VICI 360µm FS Connector – STEEL
|VICI ZDV Union
|IDEX ZDV Union
|nanoConnect Fitting – PEEK
|1/32“ Ferrules, 5pkg
|1/32“ Ferrules, 10pkg
|ZircoFit UHPLC Fittings
Any further questions or comments? Please don’t hesitate to contact us by mail (firstname.lastname@example.org).