One of the most critical areas for obtaining the best results is instrument installation and set-up. Without the right equipment and supplies, chromatographers run the risk of compromizing an instrument's potential to deliver the required level of performance. Here are some important do's and don'ts for installation and set-up.

Do Obtain a Preinstallation Checklist From the Instrument Manufacturer and Follow It

Instrument manufacturers are the best source of information about installation requirements. Following such guides is a very good habit to acquire. Detailed lists of the correct supplies and services that an instrument will require are readily available. For example, the electrical supply must be of the correct voltage and frequency, it must be properly grounded and it might require an individual connection and circuit breaker. Additional considerations, such as power filtering, surge suppressors and uninterruptible power supplies (UPSs), are important for the data handling system associated with an instrument. Also, the laboratory temperature and humidity should fall within specified guidelines. An approximate British thermal unit (Btu) output rating for an instrument helps estimate the load on laboratory air-conditioning systems. Sometimes adding a number of new gas chromatographs requires an upgrade to existing heating, ventilating and air conditioning (HVAC) systems.

The types of gases that the instrument requires depend upon the installed inlets and detectors. Capillary inlets and trace-level detectors need higher-grade gases than packed inlets or thermal conductivity detectors. The installation checklist will specify additional items such as tubing, filters and basic supplies. Appropriate gas supplies should be on-hand before an instrument arrives in the laboratory.

Many preinstallation checklists provide detailed plumbing diagrams for commonly configured combinations of inlets and detectors. Another good source of this information is available in Bulletin 898, "Gas Management Systems for GC", from Supelco (Bellefonte, Pennsylvania, USA). This publication includes a wealth of general information on gas chromatograph installation as well as detailed diagrams of appropriate connections for many combinations of pneumatic components. It covers tanks, gas generators, regulators, tubing, on–off valves, fittings, multi-tank manifolds, gas filtering, leak detection and multi-instrument installations. The brochure also contains ordering information for many recommended components.

Don't Wrap Gas Fittings with Lots of Pipe-Sealing Tape

The logic behind this practice is that more is better. I have seen white tape where it will do no good, on high-pressure tank fitting threads that do not provide a seal in the first place, as well as on the nipple-and-cup sealing surfaces where the tape is more probable to cause a leak than prevent one. Sometimes sealing tape even shows up wrapped around the ferrules of 1/4 or 1/8 in. swaged tubing fittings. The correct application of sealing tape is two layers applied to the threaded portion of pipe or tapered fittings before assembly. Remove all old tape and residue beforehand, and do not over-tighten: one-half to one turn beyond finger tight is all that is required. Wrap the tape in a direction so that it doesn't unravel when the fitting is screwed in. Never apply tape to swaged or compression fittings. Instead, use new ferrules when required.

Do Use the Correct Grade of Carrier and Detector Gas

Good, clean supplies of carrier and detector gases are well worth the expense. Get into the habit of using the right gas grade from a reliable source as the first requirement for establishing the best supply. Be sure that your gases are manufactured specifically for GC use. Select the gas grades specified by the instrument manufacturer for the exact inlet, column and detector. Although a lower grade might work, you risk encountering problems later on as contaminants accumulate or the column degrades more rapidly than it should.

Gas generators are an attractive alternative to tanks as air and hydrogen sources. The rising cost of helium carrier gas is making the switch to hydrogen more and more attractive: the cost of a high-purity hydrogen generator can be recovered after producing the equivalent of as few as eight tanks. Gas generator delivery capacities are limited, though. One generator will support a limited number of instruments, so be sure to determine in advance the total flow requirements from the number of carrier channels and detectors in use.