Essential GC Accessories

Most manufacturers ship gas chromatographs with a small collection of consumable parts and accessories, such as extra ferrules, inlet liners, or septa, and a few instrument-specific tools. In earlier times, some convenience items might have been included as well, like a bubble flow meter or a small set of tools, but now it's rare to find such things in the shipping boxes. This edition of "GC Connections" lists a number of essential items that should be on hand in every GC laboratory, their function, and how to use them effectively.  

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 plumbers', carpenters', and home toolkits. 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 may not be immediately obvious. Still others, like a column flow meter, septum nut wrench, or a specialized fused-silica column cutter, aren't found outside the laboratory at all.

Here then is an updated list of today's tools and accessories, with some information on their use and significance. One or more specialty manufacturers offer many of the chromatography-specific items; just look at their catalogs or on-line offerings. I scanned through several, and gleaned some new items that I have included here.

Source of Gas for Measuring Unretained Peak Times

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 once 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. At least one chromatography supplier offers a prefilled methane bottle with a low-pressure regulator for this purpose.

Hydrocarbons won't work for unretained peak time measurements with an electron-capture detector (ECD), because it doesn't respond. 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. Other halocarbons will work as well; check the label to be sure there is an ECD-sensitive compound present.

Hydrogen or helium-whichever is not the same as the carrier gas-makes 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 GC laboratories. Flame ionization detection (FID) will not respond to hydrogen or helium, but other detection methods such as thermal conductivity (TCD), pulsed discharge (PDD), or helium ionization (HID), the latter with hydrogen as the unretained substance, should respond well.

Remember to use the same inlet pressure and oven temperature to remeasure unretained peak times for any specific column; that is, one with the same dimensions, film thickness, and stationary phase for comparative purposes.

Caps, Capillary Column

Polymer caps for capillary columns establish an airtight seal for storage, so that air, moisture, and airborne contaminants cannot enter. I have used septa for this purpose, but there's a risk of breaking the column and puncturing a finger instead; this only happened to me once. Another approach is to seal the end of the column by melting it. This is not recommended, because it requires a hydrogen torch to achieve a high enough temperature, and it will cause stationary phase combustion by-products to migrate a significant distance into the column.

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. After inserting the column into the nut and ferrule and making a fresh cut on the column end, measure the depth and apply a small dab of correction fluid. For data integrity reasons, some regulated laboratories' policies don't permit correction fluid on site, although in the fully electronic laboratory this is moot. 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" later in this column) 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.

Cutters, Fused-Silica Column

The best fused-silica column cutting tool is the one that holds the column in an adjustable chuck, and cuts with a diamond chip as the operator rotates a thumb wheel. This tool also has a magnifying glass on the opposite end for inspecting the fresh cut for squareness and lack of burrs or hanging polyimide coating. A pen-like tool with a sapphire tip or ceramic scoring wafers or scribes that make a sharp cut on the column so that it may be broken cleanly in two are the best inexpensive alternatives. In any case, a fresh cut should be made and inspected just before placing the column into the inlet or detector, after sliding on the nut and ferrule.

Cutters, Diagonal

Diagonal cutters are used only for cutting electrical wires. They should never be used as a substitute for a tubing cutter. Don't even think about threatening your fused-silica column with one!

Cutters, Tubing

A large plumber's tubing cutter for 1/4-inch metal tubing, and a smaller one for 1/8-inch tubing, are used extensively during instrument installation and gas-supply setup. The correct 1/8-inch size cutters are available from some chromatography supply companies; don't try to use the mini cutters found in home supply stores-they're only good for those weekend plumbing projects. Keep a supply of new cutter blades on hand. These disks wear out rapidly, and a dull blade will distort the tubing diameter, and make it difficult to slide on the back and front ferrules. Power cutters with high-speed rotary abrasive cutting wheels are also available. These are mandatory for cutting 1/16-inch tubing for low dead-volume gas valving applications, and they work well for any tubing up to 1/4-inch diameter. After cutting and squaring the tubing (see "Tubing Reamer" and "Deburring Tools" later in this article), be sure to clean out the ends with a solvent, so that loose particles cannot get into the instrument components, or interfere with the passage of peaks through column ends.

Dental Mirror

A plastic dental mirror with a front-silvered surface makes it easy to examine the underside of an inlet fitting in the oven, or to check other inaccessible areas for loose or missing parts. The mirror also can be used to detect the flame in a flame ionization or flame photometric detector by observing condensation of emitted water vapor on the cool mirror surface. A shiny wrench is a good substitute for the mirror in this case.

Dental Pick

A dental pick is very handy for removing septa from septum nuts, and debris such as bits of graphite ferrule from fittings.

Eyedropper (Plastic)

I have a box of plastic eyedrops and they are in frequent demand. I use them to place small drops of isopropanol onto fittings for leak checks. Some types have rough volume indications more like a pipette, and I have used them to make a crude dilution of qualitative test mixtures when accuracy wasn't required.

Files, Needle

An assortment of needle files can be used to pick out ferrules from fittings, as well as to remove burrs and shape the ends of metal tubing before it is connected to a fitting. Don't forget to clean off all traces of metal before connecting.

Flexible Magnetic Pickup

A flexible 2-foot magnetic pickup comes in handy when you drop a small part inside the instrument. Another similar tool has a three-jawed "claw" operated by a plunger, and it will pick up non-magnetic items, too.

Flowmeter, Electronic

An electronic flowmeter is an expensive investment, but I believe that it will pay for itself many times over with improved accuracy and precision over bargain-priced bubble flowmeters. I prefer the type of electronic meter that senses flow directly, and that allows the operator to select the type of gas in use, such as air, helium, or hydrogen. The option to calculate split ratios from the measured split vent and column flows is a handy feature, but many GCs now include this capability in their software.

Flowmeters, Bubble

If you use bubble flowmeters, keep two sizes on hand. The large size is good for measuring FID air or inlet split vent flows up to several hundred milliliters per minute. The smaller size is better for packed-column or hydrogen flame-gas flows in the 10 to 50 mL/min range. Don't try to use a bubble flowmeter to measure capillary column flows below 10 mL/min. The carrier gas will diffuse out of the bubble, and you will get a low reading. Measure the unretained peak time instead, and calculate the flow rate from it. Note that this calculated flow rate or the rate displayed by electronic pressure control will only be as accurate as the column dimensions the operator uses.

Flow Measuring Adapter

Manufacturer-specific flow adapters allow a flow meter to connect to the exact dimensions of a detector's exit. Short pieces of flexible tubing in various diameters are handy for connecting a flow meter to different size tubing (see "Tubing, Plastic and Rubber" later in this article).

Glass Wool Insertion/Removal Tool

This item is useful for those who must install glass wool in inlet liners, or for the hardy few who pack their own columns and use glass wool to hold in the packing. These days I find little use for it, because I use prepacked deactivated inlet liners instead.

Gloves, Lint-free

Polymeric nitrile or vinyl lint-free gloves are essential for column installation and detector maintenance, especially for high-sensitivity detectors such as mass spectrometric, electron capture, and helium ionization types. Handling the column inlet without gloves opens the door to contamination from finger oils and dirt, while cleaning the rods of a quadrupole mass-selective detector (MSD) without gloves is asking for trouble. I recall a particular MSD that exhibited poor sensitivity. A tear-down revealed a huge thumb print on the photomultiplier tube window, perhaps deposited there by a technician who had recently finished lunch.

Hexagonal Key Set

I keep several sets of hexagonal key wrenches and drivers in the toolbox. I have sets of the traditional right-angle Allen keys in both imperial and metric sizes, as well as a collection of hex screwdrivers of both types. Although used less often, a set of star wrenches is indispensable as well. These also come in spline and security variations, some of which I've accumulated over the years. Many of these are used in laboratory instruments instead of the more traditional Phillips screw head, so they are essential for performing maintenance.

High-Temperature String

High-temperature string is a useful item for use in a GC oven to restring capillary columns, attach column connectors to column cages, or hold the column in the GC oven. The string is made of materials that can withstand temperatures of up to 400 °C, or higher.

Inlet Liner Removal Tool

A tapered high-temperature silicone rubber tool on a metal holder does a good job of grabbing glass inlet liners and removing them without cracking or chipping the liner top. Most GC instrument manufacturers will supply specific tools and instructions for a particular inlet option.

Leak Detector, Electronic

An electronic leak detector is expensive, but it indispensable for finding small leaks around hot fittings or inlets on which a liquid cannot be used (see "Leak-Checking Solution" later in the article). 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 for carrying 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 such as surfactants 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.

Maintenance Kits

Kits consisting of a collection of the most often replaced parts and supplies are a good starting point with a new instrument. Available for inlets and detectors, these packages will get used almost immediately upon commissioning. After a while, I find it convenient to re-order only those items that are used frequently instead of purchasing additional kits. The kits commonly include inlet liners, ferrules, flame jets, gauges, cleaning items, adapters, and common tools for their removal and replacement.

Mini Flashlight

A mini-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. A small short LED flashlight, the kind that you might get as giveaways at conference booths, also makes an excellent GC oven light. No one yet has built a GC oven with a light that comes on when the door is opened. A flashlight also makes a good dropped small part finder, to locate ferrules, for example. Just place the flashlight horizontally on the laboratory floor, sweep it around, and look for the shadow.

Paintbrush

An artist's paintbrush with handle is handy to clean out debris from small areas inside detectors or inlets. Just watch that a fiber from the brush does not dislodge. It can also be used to apply leak-checking solution to fittings, although I don't recommended this practice, due to 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.

Pliers

I keep some small needlenose 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-inch 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 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 getting pushed out. PTFE tape is never 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.

Rinsing Reservoir for Capillary Columns

A rinsing reservoir may be useful for reviving bonded-phase capillary columns contaminated by soluble but non-volatile sample residues. Solvent rinsing is intended for use only after bake-outs and trimming of about 0.5 m of the inlet end plus the exit portion that enters the detector heated zone have failed to restore performance. Use only the solvents that the column manufacturer recommends, and rinse only from the detector end to the inlet end to avoid depositing contaminants deeper into the column. Check and revalidate column performance after rinsing.

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 never to be used to cut fused-silica columns (but you can believe that I've seen someone try it).

Screwdrivers, Phillips-Head

I have three Phillips-head screwdrivers in the toolbox: large, medium, and small. The small one is part of a set of jeweler's screwdrivers with rotating handles. These are general purpose items that any laboratory should have on hand.

Screwdrivers, Slotted-Head

I also keep three slotted-head screwdrivers. The small one is useful for securing electrical connections to screw-type terminals.

Septum Puller

This is a specialized tool for removing septa that become stuck due to heat-adherence to the inside of the septum area of an inlet. I have also used a dental pick for this purpose. Avoid using a flat-bladed screwdriver or a knife, because these may scratch the metal surfaces that seal to the septum.

Static Pad

A static pad is a grounded, conductive plastic sheet onto which it is safe to place electronic components that must be protected from damaging electrostatic discharge. Any circuit boards removed from an instrument should be placed on a grounded static pad, or in a static-proof bag.

Static Wrist Wrap

A grounded static wrist strap prevents the technician from imparting a potentially harmful static discharge into instrumentation or components. Always wear one when working inside an instrument or removing components, and in all cases be quite sure that the instrument power has been removed while the instrument itself remains grounded.

Stopwatch, Digital

A digital stopwatch times bubbles in a bubble flowmeter, and also times an unretained peak. It's often more convenient to use a stopwatch when setting up an instrument than to operate the chromatography data system for each test injection. Select a stopwatch with readout to 0.01 second. Some GC systems include a stopwatch function on the display that includes flow, split ratio, and linear velocity calculations. These days, I just use my smart phone's stopwatch and timer functions, and then its calculator to find flow rates or average linear velocities. Good phone applications are available with additional chromatography functions.

Swabs

Recently I have used polyester swabs, mostly intended for cleanroom use, for cleaning out inlets and detector bodies. Take care that the solvents used are compatible with the swab material. Methylene chloride, for example, will dissolve polyester readily. I don't like to use cotton-tipped swabs on a wooden stick. Not only will the cotton release fibers, but the wood may release higher molecular weight compounds into cleaning solvents.

Syringe

I keep two manual syringes for setup purposes. One 10-µL gas-tight syringe is for injecting methane or butane to measure the unretained peak time and ascertain that the flame is lit and carrier gas is flowing. The other is for making liquid test-mixture injections as part of a column checkout. Sample syringes are kept separately.

Syringe-Cleaning Wires

Syringe cleaning wires may be used in an emergency to clear septum particles or other debris from syringe needles. I recommend discarding stubborn contaminated syringes; take steps to keep the syringe clean instead.

Text Mixtures

Column and detector test mixtures verify column performance and detector sensitivity. Keep a fresh vial of each type on hand, and put them in the chemical refrigerator if the label so directs. Column test mixtures are available for polar and for non-polar capillary columns, and there are test mixtures for each detector type. Some manufacturers provide a detector test mix that combines components for testing several different detectors. Once opened, test mixtures can be kept for a while in septum-sealed vials. Their lifetime is limited, because of gradual evaporation. If you keep test mix in a vial, remove the vial cap rather than puncture the septum when withdrawing liquid for injection. Some laboratories find it more convenient to keep dilute test mixtures on hand, because these are more easily disposed of than the concentrated mixes. Many laboratories have their own qualification and validation standards, of course, but the manufacturer's mixtures allow easy comparison to the factory test results, and may be used for a factory-level checkout.

Tube Blender

I use this simple tool to make controlled bends of copper or stainless steel tubing for connecting the supply tanks to the filters, and then to the back of the instrument. It makes for a clean and organized looking installation. Tube benders come in sizes to fit standard tubing diameters.

Tube Reaming and Deburring Tools

These tools are used to remove burrs and irregularities from metal tubing after cutting. They are available for the standard tubing diameters, and I highly recommend using them in order to ensure leak-free connections. As always, be sure to clean off any loose metal particles or shavings.

Tubing, Plastic and Rubber

I keep several pieces of black and clear silicone rubber tubing on hand for connecting my flow meter to column ends, split vents, and other flow sources. The narrower pieces of tubing fit inside the wider ones so that I can adapt the flow meter fitting to a variety of connections. I have some silicone tubing that seals nicely to 1/16-inch tubing, and then slides into the flow meter's 1/8-inch inner diameter inlet tubing. We ordered a small spool of this silicone tubing, because it was always disappearing into other locations in the building. Of course, I never use plastic or rubber tubing for any gas at elevated pressure, or for permanent supply or internal connections.

Tweezers and Hemostats

A pair of tweezers can hold small nuts or ferrules without risking contamination with skin oils or a burn from hot items. Some tweezers have a convenient locking feature that frees one hand for other tasks, as will a spring-loaded hemostat. Rubber tips help hold fragile capillary columns or inlet liners.

Vial, Autosampler

I keep a spare autosampler vial to check for carrier gas flow during column installation. Fill the vial halfway with distilled water, and then insert the column outlet after connecting to the inlet but before connecting to the detector. After turning on carrier gas pressure, the presence of bubbles shows positive carrier gas flow. Never heat a column until you are sure there is positive flow through it.

Vial Crimper

Vial crimpers attach aluminum crimp-top seals to autosampler vials. Several crimp-top sizes are commonly used for GC: 8-mm for 0.8-mL vials, 11-mm for 1.5 or 2.0-mL vials, and 20-mm for 5-mL and 20-mL headspace vials. Hand crimpers are the least expensive, and some are available with interchangeable jaws that accommodate different vial sizes. Automated bench-top crimpers are less mobile, but the jaws can be interchanged quickly, and they are best for laboratories with high sample throughput. I prefer the type with rechargeable batteries.

Vial Decapper

Vial decappers perform the opposite function of a crimper; they remove crimp-top seals from vials. Decappers come in the same sizes as the crimpers, and resemble a pair of pliers. Some caution is required in use, so as not to break the neck of the vial. Once caps are removed, the contents may be properly disposed. Some laboratories reuse sample vials, but I recommend a fresh vial for each sample if at all possible.

Wipes, Laboratory

I wet laboratory wipes with some isopropanol, and then clean any debris or oil off the ends of capillary columns before inserting them into inlets or detectors. They also are handy for tipping a drop of test mix off a syringe needle, if disposed of properly. Paper towels don't work as well; they may leave fibers behind, and they may deposit a chemical residue. I recently have started to use particle-free cleanroom type wipes premoistened with a mixture of 70% isopropanol and 30% deionized water.

Wire Brushes

Wire brushes can dislodge particles and debris from detector parts and some sealing surfaces. Be careful not to score polished metal surfaces, or damage ceramics. It is better to replace a severely dirty FID flame jet or collector than to clean it forcibly. The manufacturer's guidelines for cleaning will have ways to assess the reusability of these parts.

Wrenches, Adjustable

I have one large 18-inch long adjustable wrench that looks like it belongs in an automotive garage. This is used exclusively for attaching or removing pressure regulators on gas tanks. I also have a smaller 6-inch long adjustable wrench that I use occasionally, if someone else has walked off with the exact open-ended wrench size I need.

Wrenches, Open-Ended

I have an assortment of open-end wrenches in inch sizes, as well as a metric set. I keep two or three with the following sizes: 1/4-, 5/16-, 3/8-, 7/16-, 1/2-, and 9/16-inch, as well as 11/16-, 3/4-, and 1-inch, although these latter sizes are used only rarely. Chromatographers located outside the United States will find the standard metric wrenches to be a bit more useful. I apply two wrenches at once to prevent counter-rotation while tightening or loosening fittings.

Conclusion

Chromatographers, like all craftspeople, use a variety of tools to practice their craft. In a pinch, tools that are somewhat inappropriate can be used to make do, but the rapidity and ease with which the right tool gets the job done make it well worth the expense of obtaining what's needed for the job.

ABOUT THE COLUMN EDITOR

John V. Hinshaw

John V. Hinshaw "GC Connections" editor John V. Hinshaw is a Senior Scientist at Serveron Corporation in Beaverton, Oregon, and a member of LCGC's editorial advisory board. Direct correspondence about this column to the author via e-mail: LCGCedit@ubm.com