A GC Troubleshooter's Toolkit

Jul 01, 2012
Volume 30, Issue 7, pg 570–577

It has been about nine years since this list was last published in LCGC (1). During the interim, my toolbox has gained some new items, and a few others have seen little or no use. Given the modern obsession with list-making, readers may enjoy this update and perhaps learn about some tools they might like to add or replace in their own toolkits.

Every profession has its specialized tools. Those used in chromatography often are just as specialized as those used in computer repair or automotive work. Many of the tools and accessories that gas chromatographers keep on hand for installing, maintaining, and repairing their chromatographs are also found in the toolkits of plumbers, carpenters, and homeowners. Wrenches, screwdrivers, pliers, and metal-tubing cutters are some easily recognized examples. Other items such as dental instruments or paper correction fluid are familiar, but their use in the laboratory environment might not be immediately obvious. Still others, like a column flowmeter, septum nut wrench, or a specialized fused-silica column cutter, aren't found outside the laboratory at all.

Here, then, is the list of today's tools and accessories along with some information about their use and significance. One or more specialty manufacturers offer many of these chromatography-specific items in their catalogs or on-line offerings. I scanned through several catalogs and web sites and gleaned some new items that I have included here.

Butane Lighter

A butane lighter is a convenient source of hydrocarbon gas for measuring an approximate unretained peak time. Butane is effectively unretained at temperatures above 75 °C on liquid-phase coated columns with phase ratios above 50. Columns at low temperatures or with lower phase ratios (thick stationary films) may retain butane and separate the traces of ethane and propane present in the butane fuel. Use the earliest observable peak for the best estimate of unretained peak time. Natural gas is mostly methane; if your laboratory has a supply of natural gas (mine doesn't) it makes a good substitute for a lighter and is less retained than butane. Just be sure to turn off the gas after you've filled a syringe with it. A lecture bottle of methane with a suitable pressure regulator is another excellent source of the unretained substance. Concentrations in the low percent range work well.

Hydrocarbons won't work for unretained peak time measurements with electron-capture detection (ECD). Instead, try loading the syringe with a puff from a pressurized can of dust remover such as Dust-Off, which contains 100% 1,1-difluoroethane.

Hydrogen or helium — whichever is not the same as the carrier gas — make good unretained peak markers for porous polymer or molecular sieve columns that retain hydrocarbons strongly, plus these two gases should be readily available in most gas chromatography (GC) laboratories. Flame ionization detection (FID) will not respond to hydrogen or helium, but other detection methods such as thermal conductivity detection (TCD), pulsed discharge detection (PDD), or helium ionization detection (HID), the latter with hydrogen as the unretained substance, should respond well.

Cable, Three-Wire

Recorder cable finally has gone the way of chart recorders: You might find some lying around but they haven't been used in years. I have one or two in the lab just in case the need arises. I keep some spare USB cables as well.

Correction Fluid

Use white correction fluid to mark the measured position on a column that corresponds to the correct column penetration depth into an inlet or detector. Measure the depth after inserting the column into the nut and ferrule and making a fresh cut on the column end. Some regulated laboratories' policies don't permit the use of correction fluid for data integrity reasons. A septum into which a slot has been cut may be slid onto the column below the nut and ferrule to act as a positioning aid. Remove the septum before heating the column oven. A positioning gauge (see "Ruler" below) is a good alternative. I also have used a black permanent marker for this purpose; just be careful not to get it on your fingers or clothing.

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