A GC Troubleshooter's Toolkit - - Chromatography Online
A GC Troubleshooter's Toolkit


LCGC North America
Volume 7, Issue 30, pp. 570-577

Leak Detector, Electronic

An electronic leak detector is expensive, but it is indispensable for finding small leaks around hot fittings or inlets on which a liquid cannot be used (see "Leak-Checking Solution" below). The most sensitive type of leak detector uses a small pump to pull air from a probe through a thermal-conductivity cell. The presence of carrier gas or hydrogen changes the thermal conductivity and causes a change in the detector's readout compared to a reference air flow. Sensitivity for nitrogen carrier is limited. I also have a small handheld, battery-powered leak detector that has a series of light-emitting diodes which indicate the detected leak rate. This detector is great to carry around in a laboratory like mine with lots of instruments and little clear bench space.

Leak-Checking Solution

In my toolbox, the only acceptable leak-checking solution is a small bottle of pure isopropanol with an eyedropper. Other solutions may contain material that can leak into the gas-supply lines or columns and cause ghost peaks or other contamination.

Magnifier

A small magnifier is used to examine freshly-made column or tubing cuts for burrs or uneven edges.

Manufacturer-Specific Tools

For each GC system, there are always some specialized tools. These are used, for example, to open up a split–splitless inlet or to remove the inlet liner. Perhaps a special wrench is required for FID system flame jet replacement. Whatever the case, keep all such tools with their instrument: you will need them eventually. Some of the chromatography suppliers offer their own versions of these tools, which often are more useful than the freebie ones that come with the instruments. Several companies have toolkits for a specific popular instrument that is a must-have item for me.

Mini Flashlight

A flashlight is very handy for inspecting the interior of inlets and detectors for obstructions, as well as for illuminating the oven interior. I prefer the type with the bulb on a flexible gooseneck. No one yet has built a GC oven with a light that comes on when the door is opened.

Nuts, Capillary Column

There are several different styles of capillary column nuts that are used in the GC oven. My toolkit includes some of each type for my instruments. I never try to substitute one for another, even though the thread sizes are the same.

Nuts, Metal Tubing

Nuts for metal tubing are more standardized than capillary column nuts. Swaged fittings normally are used for outside tubing connections and often for internal connections as well. Keep an assortment of 1/4-in., 1/8-in., and 1/16-in. sizes on hand. Don't try to mix nuts and fittings from different manufacturers. I've picked one type and tried to purge all the others from my lab, so I don't have to peer at the small letters on each fitting to discern its type.

Nut Drivers

Handheld nut drivers are a useful addition, but I find that I use them more at home than in the laboratory.

Paintbrush

An artists' paintbrush with handle is handy to clean out debris from small areas inside detectors or inlets. It can also apply leak-checking solution to fittings, although I don't recommend this practice because of potential contamination of the gas stream with the leak-checking solution.

Paper Clips

Jumbo-size paper clips with smooth sides are convenient for blocking off inlet or detector fittings for testing purposes. Unbend the clip and attach it to the fitting with a nut and 1-mm i.d. graphite-vespel ferrule. With the column connection blocked off, you can pressure-check an inlet. A detector check can be run in this manner without column influences on noise or stability.

Pin Vise and Drills

A small pin vise and a set of drills can be used in an emergency to drill out a used ferrule or to enlarge one that is too small to fit a column. Sometimes the small drills can help to remove a ferrule that is stuck in a fitting or to remove debris from inside fittings or tubing ends.


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