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UltiMetal Plus Flexible Metal ferrules and Self Tightening Column Nuts stop leaks to protect GC columns

By Ken Lynam
Agilent GC R&D/Applications Chemist

As we discussed in last month’s article about robust, leak-free connections, leaking column connections are major causes of high background noise and poor gas chromatography. We saw how the new Agilent Self Tightening Column Nut ensures leak-free connections without the need for wrenches or adaptors. In addition, Agilent has other solutions to help achieve leak-free connections and improve the integrity of the GC flow path. This month, we describe the Agilent UltiMetal Plus Flexible Metal ferrule, show how it compares with the Agilent Self Tightening Column Nut, and help you decide which connector is correct for your application.

Tight specifications lead to robust column connections

The length of column installed in the GC inlet impacts sample transfer to the column and resulting data reproducibility. For accurate and reproducible results, you must properly measure the length of column inserted into the inlet and hold that length constant every time you install a column or retention gap in the inlet.

Because they firmly grip the column, flexible metal ferrules can improve the consistency of column installation in the inlet. Once you measure the proper column length, you can permanently pre-swage the flexible metal ferrule onto the column tubing. There is no sliding or moving of a pre-swaged flexible metal ferrule, so you maintain the properly measured length – without the need for an inlet septum or other means to try to hold the ferrule in place.

When you use Agilent UltiMetal Flexible Metal ferrules, you no longer need to worry about column breakage and retightening during use, because the stainless steel design holds its shape in the fitting during thermal cycling. This novel design, together with tighter specifications and tolerances of ferrule internal diameter, allows secure and consistent sealing with less torque than other metal ferrule designs. In addition, you eliminate spontaneous column breaks due to catalytic degradation of the polyimide coating of the column at high temperatures.

The Agilent UltiMetal Flexible Metal ferrule has a larger inner diameter on the nonsealing end, and that lets you easily thread the column through it. In addition, the ferrules have a unique appearance (Figure 1), so you can easily distinguish them when you select the appropriate ferrule for the column.

Figure 1. Agilent UltiMetal Plus Flexible Metal ferrules have different shapes to help match ferrules and columns.

UltiMetal Plus Flexible Metal ferrules provide inert connections

If you work with GC/MS in the food, environmental, or forensic industries, you are well aware of the importance of an inert flow path when you perform trace-level analyses of very active compounds. Ferrules can be an integral part of the flow path, with surface exposed to the sample.

Studies have shown that exposure to a very small surface of nondeactivated metal can completely adsorb active compounds. The UltiMetal Plus deactivation on the surface of the flexible metal ferrules provides an inert connection between the column and retention gaps. This inert connection is important when you use Agilent Capillary Flow Technology, such as the Agilent Ultimate Union, effluent splitters, or backflush devices.

To sustain flow path inertness, the Agilent UltiMetal Plus Flexible Metal ferrules are also used at the inlet column (or retention gap) connection. Because the ferrule is not in contact with the sample at the mass spectrometer interface, ferrule inertness is not a requirement for this critical column connection. However, a leak-free fitting is essential at the mass spectrometer transfer line.

Ferrule or nut?

As we have seen, the UltiMetal Plus Flexible Metal ferrule grips columns without crushing them, so it prevents column breakage and damage to fittings. It is also highly inert for trace-level analyses and it provides robust, leak-free column connections.

Another connection option is the Agilent Self Tightening Column Nut, which uses short graphite/polyimide ferrules to deliver a leak-free seal, even at high temperatures. The nut’s easy fingertight design requires no retightening and is ideal for use with short graphite/polyimide ferrules and with inlet, detector, and MS transfer lines. Table 1 shows which connector to use, depending on your requirements.

Table 1. Choose the Self Tightening Column Nut or Flexible Metal ferrule for your application.

Reproducible results from essential GC supplies

This article is just part of our story on Making Better GC Connections, so look for another chapter in next month’s Access Agilent. The upcoming chapter will describe the most critical GC connection “hot spots” and provide tips to fix problems before they compromise results. In the meantime, you can always learn more about getting the best from your GC with Agilent Inert Flow Path solutions and Agilent J&W Ultra Inert GC columns.

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