Frequently Asked Questions (FAQs): GC Accessories

1. What ferrules do I use with my column?
2. How do I connect a fused silica guard column to a fused silica GC column?
3. How do I install a column in my gas chromatograph (GC)?
4. Why can’t I get my Press-Tight connector to seal?
5. What is a drilled Uniliner inlet liner?
6. How do I clean my inlet liners?
7. Why shouldn’t I use liquid leak detectors?
8. What gases will my Restek electronic leak detector detect?
9. What fitting do I need to remove a gas sample from an NPT outlet (such as from a regulator) with a syringe?
10. Can Restek provide replacement filters and catalyst towers for Parker zero air generators?
11. How do I dispose of used gas traps or filters?
12. What liner do I need for…?
13. What septa should I use?
14. How long will my Merlin Microseal last?
15. Can an MXT-Union connector be used to connect fused silica capillary columns with different IDs?
16. Can Restek liners be re-deactivated?
17. Should there be an O-ring between my Restek filter and the baseplate it is mounted on?
18. I need a fitting to…
19. Which injector part is the shell weldment, and which is the weldment?
20. What syringe needle point styles are available?
21. I cannot tell if this is the syringe I want. What do all the letters mean?
22. When should I use a 0.8 mm ID inlet seal, and when should I use a larger ID?

If your question doesn’t appear on the list, please contact Restek’s Technical Service group.
(Remember to include your company name and complete mailing address.)

1. What ferrules do I use with my column?

 

One-piece ferrules are available in two designs: the standard 1/16-inch compression type and the short, compact design. Agilent GCs typically use the compact design at the injector and detector, but we always recommend using the 1/16-inch compression type ferrule at the detector if you are doing GC-MS analysis. Whichever configuration you select, it is essential that you use the corresponding standard or compact nut.

In addition, ferrules are generally available in three compositions: graphite, Vespel, and Vespel/graphite. Composition is usually a matter of preference, but we recommend Vespel/graphite ferrules for GC-MS because they seal with minimum torque, maintain sealing performance under high pressure and vacuum, and are reusable.

The hole in the ferrule should always have a slightly larger inner diameter (ID) than the column’s outer diameter (OD) so that it can compress and seal around the column. For example, a 0.53 mm ID Restek column, which has an OD of approximately 0.7 mm, would require a ferrule with an ID of 0.8 mm.

For more on ferrule selection, see our blogs on ferrule selection and our GC nut/ferrule compatibility chart. You’ll find specific information there for all the major instrument brands.

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2. How do I connect a fused silica guard column to a fused silica GC column?

 

Restek offers several choices. The Defined PressFit connectors and Press-Tight connectors are glass connectors with a tapered internal diameter at each end and are the quickest and least expensive option. The SilTite μ-Union connectors are another alternative; these connectors are constructed of deactivated metal and provide easy installation and a zero-dead-volume, permanent leak-tight connection, which makes them ideal for use with mass spectrometers. A popular and effective option is the MXT-Union connector, which will not break and ensures low dead volume.

Our Vu2 Union connector and SeCure "Y" connector combine the simplicity of a Press-Tight connector with the strength of a metal union and can be used to a temperature of 400 °C.

3. How do I install a column in my gas chromatograph (GC)?

Follow the recommendations on the GC column installation guide, which is included with most columns. If an installation card is not available, visit our capillary column installation guide.

4. Why can’t I get my Press-Tight connector to seal?

 

Defined PressFit connectors and Press-Tight connectors are easy to use, but if they are not properly sealed, they can loosen due to thermal expansion during temperature-programmed runs. The keys to successful sealing are (1) making a clean, square cut on the column, and (2) moistening the end of the column with methanol or acetonitrile before seating it into the connector. A small amount of polyimide resin also helps prevent the seal from separating during temperature cycling.

For complete instructions on using the Press-Tight connector, consult the document included with the product or reference the Universal Fused Silica Press-Tight Connectors instruction sheet here.

5. What is a drilled Uniliner inlet liner?

 

The drilled Uniliner was designed and developed specifically for making direct injections in an Agilent GC equipped with electronic pressure control (EPC). A hole in the wall of the liner, near the inlet end or the outlet end, equalizes pressure and makes the liner compatible with EPC.

The pneumatics for EPC in the Agilent GC consist of two pressure sensors, one upstream from the injector and one downstream from the injector, at the split vent. When a standard Uniliner inlet liner is used for direct injection, it is sealed to the analytical column. Consequently, there is no downstream flow of carrier gas to the pressure sensor at the split vent. A pressure difference between the two sensors is detected and the upstream sensor overcompensates, causing a high-pressure malfunction and shutdown of the GC. The drilled Uniliner allows a portion of the carrier gas to escape from the liner and equalize the pressure at the two sensors. The drilled Uniliner requires no software or hardware modifications, or flow adjustments. For optimum performance, we advise using drilled Uniliner inlet liners in splitless mode.

6. How do I clean my inlet liners?

All liners gradually become dirty and the surface becomes active, making them unsuitable for most samples. Cleaning a liner will never return the liner to its original level of deactivation, and in many cases, it is cheaper to replace the liner and ensure high quality and consistent deactivations.

To clean a liner with no visible deposits or discoloration, it is best to rinse the inside with the following solvents in sequence:

1. methanol,
2. then methylene chloride,
3. then hexane.

Use a cotton swab or pipe cleaner to gently scrub the inner surface of the liner, but be very careful not to scratch the liner and thereby remove the deactivation layer. If deposits are visible or the liner is discolored, it may be necessary to ultrasonicate the liner in methanol, then methylene chloride, and then hexane. Some deposits must be removed by heating the liner to 450–500 °C for one hour. These temperatures will remove some deactivation layers but will not harm a Siltek coating. Higher temperatures can soften the liner itself. Heat treating a liner to remove stubborn organic matter will remove the deactivation, not remove all of the organic matter or other non-chromatographable material, and will require re-deactivation. Re-deactivation processes available to chemists in the lab require time and reagents, are somewhat dangerous, and produce toxic waste materials. Furthermore, the quality of the re-deactivation is never as good as the original liner deactivations. When all costs are considered, replacement often is less expensive.

7. Why shouldn’t I use liquid leak detectors?

Some common liquid leak detectors, such as Snoop products, are soap solutions. These solutions are easily drawn into the pneumatic system, analytical column, and detector by Venturi flow. Because soap solutions can cause irreparable damage to a GC column, they should never be used. If necessary, you can use a 50/50 mixture of water and isopropanol as a liquid leak detector that will not damage your column. Many liquid leak detection fluids have limited usefulness on hot fittings (i.e., above 100 °C) because they boil away. A Restek electronic leak detector is always the best choice because it is more sensitive, and it will not damage the column.

8. What gases will my Restek leak detector detect?

The Restek electronic leak detector will detect minute leaks of any commonly used carrier, fuel, or make-up gas with a thermal conductivity different from air. The reference gas inlet on the back of the leak detector draws in ambient air for comparison to the gas sample drawn into the sample probe stylus. A thermal conductivity difference between the two indicates a leak, and the leak is revealed by both an LED display and an audible tone.

*Caution: The Restek electronic leak detector is designed to detect trace amounts of hydrogen in a noncombustible environment. It is NOT designed for determining leaks in a combustible environment. A combustible gas detector should be used for determining combustible gas leaks under any condition. When using it to detect hydrogen, the Restek electronic leak detector may only be used for determining trace amounts in a GC environment.

9. What fitting do I need to remove a gas sample from an NPT outlet (such as from a regulator) with a syringe?

 

For a 1/8" NPT outlet, use male connector cat.# 23133 (for a stainless-steel fitting) or cat.# 21841 (for a brass fitting), and a Shimadzu plug septum. For a 1/4" NPT outlet, use male connector cat.# 21942 (for a stainless-steel fitting) or cat.# 21842 (for a brass fitting), and a 9.5–10 mm septum.

10. Can Restek provide replacement filters and catalyst towers for Parker zero air generators?

Yes, we supply maintenance kits: cat.# 21646 for Model 75-83NA, cat.# 21647 for Models HPZA-3500, HPZA-7000, HPZA-18000, HPZA-30000, and catalyst towers: cat.# 22005 for Model 75-83NA, cat.# 22004 for Model HPZA-3500, cat.# 22006 for Model HPZA-7000, cat.# 22007 for Model HPZA-18000, and cat.# 22008 for Model HPZA-30000. Note: To keep costs down, catalyst towers are shipped from the supplier.

11. How do I dispose of used gas traps or filters?

Because components in the trap/filter; use of the product; and local, state, and federal regulations can all vary; you should contact your waste disposal company for guidance. Neither the seller nor the manufacturer has a program available to return gas traps or filters for disposal.

Related blog articles:

• Contents Inside Your Baseplate Trap
• SDSs for 22010, 22011, 22014, and 22015 (Indicating Oxygen & Moisture Traps/Filters)

12. What liner do I need for…?

In order to select the proper liner, you must first know your application needs:

• Split injection is typically used for samples that are dirty and/or have a broad range of analyte concentrations. Split injection must quickly and completely vaporize the sample into a homogenous cloud, and there are numerous liner designs that achieve this. The most common is the straight tube packed with fused silica wool. Alternate designs include the laminar cup, frit splitter, cup splitter, cyclo, baffle splitter, and mini-Lam splitter, all of which are designed to facilitate rapid, homogenous vaporization, yield reproducible performance, and minimize molecular weight discrimination.
• Splitless injection is typically used for trace-level analyses. Generally, the liner should have a taper design (single, double, or recessed) to help contain the vapor cloud in the liner during the extended hold time and to minimize the breakdown of compounds sensitive to catalytic decomposition from contact with metal inlet surfaces. The single taper design is used with a single column; the recessed design can be used for a dual-column application. Both are routinely packed with fused silica wool.
• Direct injection liners connect the column to the bottom of the inlet sleeve. This allows the sample to be swept directly into the column, eliminating injection port discrimination and sample contact with hot metal surfaces. Direct injection liners are available for packed column or capillary splitless injectors. We recommend a drilled Uniliner inlet liner for capillary split/splitless injection ports.

All liners, regardless of application, should always be deactivated. We also recommend that, whenever possible, they be packed with deactivated glass or fused silica wool to facilitate uniform sample vaporization and trap nonvolatile residue, thereby preventing column contamination.

13. What septa should I use?

Select septa based on the injection port temperature you will use. Generally, septa with lower thermal limits are softer, and thus are easier to seal or to pierce with a needle. However, softer septa are more prone to damage caused by overtightening the septum nut, and this can reduce the life of the septum. Change all septa regularly, regardless of their thermal limits, to avoid coring and bleed. Use Thermolite Plus septa at inlet temperatures* up to 350 °C, and premium non-stick BTO septa to 400 °C. For tips on preventing septum problems, read our helpful technical article.

*Note: Due to differences in inlet design, the actual septum temperature for a given inlet set point can vary by manufacturer. Restek recommends using only BTO septa in older Thermo TRACE and Focus GCs. For Thermo TRACE 1300/1310, 1600/1610 GCs, this recommendation does not apply; septa can be used to their maximum recommended temperature. For 17 mm inlets, the maximum temperature is 330 °C (for Thermolite Plus the max. temp. is 300 °C).

14. How long will my Merlin Microseal last?

Merlin Microseal lifetimes can vary widely depending on sample composition, operating conditions, and laboratory environment. Usual lifetime ranges from as few as 1,000 to well over 10,000 injections. For more information, consult the Merlin Microseal User Manual.

15. Can an MXT-Union connector be used to connect fused silica capillary columns with different IDs?

Fused silica adaptor ferrules will enable you to use an MXT-Union connector to join fused silica capillary columns with different IDs.

16. Can Restek liners be re-deactivated?

Restek offers re-deactivation services for polymeric and base-deactivated liners. Pricing is available on request and depends on the number of liners returned—the more liners you return, the lower the re-deactivation cost per liner. Contact Restek Customer Service for more information or a quote. Often a liner simply needs to be cleaned, not re-deactivated. See "How do I clean my inlet liners?" above for details. Note that Restek Premium liners cannot be re-deactivated. Also, Siltek liner re-deactivation is not available through Restek, but more information can be found here.

17. Should there be an O-ring between my Restek filter and the baseplate it is mounted on?

To protect the baseplate, it is shipped with a cover, also called a "flush cap," held in place by a universal ring nut. There is a large O-ring (about 1 inch in diameter) between the baseplate and the flush cap. Sometimes this O-ring falls out, leading the user to question if the O-ring should be on the baseplate when attaching a filter. The O-ring should stay with the flush cap. If the O-ring is left on the baseplate, the filter will not seat properly and there will be no flow through the system. The proper procedure is (1) unscrew the universal ring nut, (2) remove the flush cap and O-ring, (3) attach the filter cartridge, and (4) then secure it by screwing the universal ring nut back on the assembly.

18. I need a fitting to…

Two basic types of fittings are used for analytical instrumentation: National Pipe Thread (NPT) and compression, both of which are available in stainless steel or brass. Stainless steel is the best choice for fittings that will be routinely loosened and tightened; the threads on brass fittings are more susceptible to damage caused by repeated tightening. Never mix stainless steel fittings with brass fittings because of the potential for damage to the softer brass by the harder steel. Similarly, stainless steel fittings generally should be used with stainless steel tubing, brass fittings with copper tubing. For more on fitting selection, view our blog article.

19. Which injector part is the shell weldment, and which is the weldment?

The shell weldment in an Agilent 5890 GC is a boxlike part that attaches to the top of the GC with screws. The inlet body projects down from the shell weldment and extends into the injector heater block. The liner (typically glass) is placed in the inlet body. The gas-line port that projects from the side of the shell weldment, near the top, is the split vent. The weldment, which looks like a cap, screws down on top of the shell weldment. The septum is placed in the weldment and is held in place with the septum nut. The gas lines that connect to the weldment are for the carrier gas and septum purge gas. (The carrier gas line has the smaller ID.) For help selecting replacement weldments and shell weldments, view our blog article.

20. What syringe needle point styles are available?

Restek offers several different point styles on syringe and needle products. Choose one based on your application. Other styles are available on request.

21. I cannot tell if this is the syringe I want. What do all the letters mean?

Codes on a syringe indicate the type of needle (fixed or removable), the point style or shape of the needle, and other information. For convenience, we usually also list the manufacturer's part number in the same table as the syringe.

From cemented to removable needles, and from PTFE luer lock to special syringe fittings, syringe barrel terminations create the interface between a syringe and its mating connection. For your reference, we describe the most common Hamilton/SGE terminations below.

22. When should I use a 0.8 mm ID inlet seal, and when should I use a larger ID?

The 0.8 mm ID inlet seal is used for all single-capillary column installations-whether the column is 0.25 mm, 0.32 mm, or 0.53 mm ID. The 1.2 mm ID inlet seal is used for a dual-column installation with 0.25 mm and 0.32 mm column IDs. A 1/16-inch ID opening inlet seal is used for the installation of two 0.53 mm ID columns or a micropacked column.

Note: Most single-column installation fittings (i.e., nuts) do not work with dual-column installations or dual-hole ferrules. For these applications, a kit such as cat.# 27185 or 20645 may be needed (e.g., with Agilent injection ports) in addition to a different inlet seal.