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


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

Pliers

I keep some small needle-nose pliers, a pair of larger multigrip pliers, and one pair of locking pliers in my toolkit. The larger gripping pliers are useful for holding a straight length of 1/8- or 1/4-in. metal tubing while cutting it, although I take care not to grip the tubing anywhere near a location where a connection is to be made because the scratches from the pliers would make it impossible to get a good seal.

Press-Fit Connectors

Glass press-fit connectors make it easy to repair a broken column temporarily (until a replacement can be installed). These are available in many sizes to connect fused-silica tubing of the same or different diameter. They also connect a column with a retention gap. One manufacturer now offers a vacuum–melting device that makes near-perfect connections.

Pressure Gauge, Inlet

I have a conventional 0–60 psig pressure gauge with a syringe needle attached that I can insert into an inlet through the septum. Once in a while I need to check the inlet pressure this way, instead of relying on the instrument's gauges or electronic pressure readouts.

PTFE Tape

PTFE tape is used sparingly on tanks and interconnecting fittings where threads form the seal. Use two layers of tape, not more, and wrap them around the threads in the direction the nut tightens so that the tape will be drawn into the fitting instead of pushed out. PTFE tape should never be used in swage-type ferrule-sealed fittings, where it will only cause a leak, nor is it used at the high-pressure supply cylinder connection. Several types of this tape are available; be sure to select the right one.

Ruler

A small metal ruler measures the correct column penetration depth into an inlet or detector. Don't use a plastic ruler, because it might melt in contact with heated inlets or detectors. For convenience, make marks on the ruler that correspond to the correct inlet and detector depths. Several manufacturers offer capillary column installation gauges with the appropriate markings.

Scissors

A good sharp pair of scissors comes in handy for opening packages of ferrules, or for making paper stars out of waste paper that's waiting to be recycled while watching for peaks to be eluted. Scissors are not to be used to cut fused-silica columns (but you can believe that I've seen someone try it).

Screwdrivers, Phillips-Head

I found three Phillips-head screwdrivers in my toolkit: large, medium, and small. The small one is part of a set of jeweler's screwdrivers with rotating handles.

Screwdrivers, Slotted-Head

I also keep three slotted-head screwdrivers. The small one is useful for securing electrical connections to screw-type terminals. My set of jeweler's screwdrivers in a small plastic box have a knurled body and a separately-rotating knob that make it easy to turn the shaft with one hand. They haven't seen too much GC use, but they are good for tightening the frames of my eyeglasses.

Seals, Inlet

Many capillary inlets use an internal O-ring seal to isolate the incoming and exiting split flows. These seals are available in a variety of materials, including silicone, graphite, and high-temperature polymer. Worn seals will cause internal leakage and performance losses. Keep a good assortment on hand for each instrument. Some instruments use a metal seal and washer at the bottom of split–splitless inlets. For these, I prefer the deactivated seals available from at least one supplier. A seal with a Vespel seating surface for the inlet liner was recently made available, as well.

Septa

Spare septa are a requirement. Septa should be changed often. If you wait until retention times begin to drift upward then it's too late — a significant leak that will compromise results already has developed. Keep both normal-temperature range septa as well as some high-temperature ones on hand. I handle my septa — and all internal inlet parts — with tweezers or cotton gloves: a little bit of finger contamination can create a significant baseline bleed level.


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