Gas Management Supplies for GC Labs
A clean gas stream is critical to the quality of your GC analysis and the reliability of your analytical results. Carrier gas must contain less than 1 ppm of oxygen, water vapor, and other trace contaminants for stable baselines on all detectors and to prevent column degradation, shortened column lifetime, and increased stationary phase bleed. Clean fuel gases and make-up gases are also essential for stable detector baselines. Your gas management system must deliver a high-purity gas stream from your source to your instrumentation without introducing contaminants. Restek offers the products you need to assure a clean, leak-free gas management system. If you need assistance in configuring your system, contact your Restek representative to discuss your application requirements.
Questions to consider when building your gas management system:
- What gases do you require and at what purity?
- What flow rates and/or pressures are required?
- Are you using gas generators or high-pressure cylinders?
- What type of tubing and fittings are needed to build your system?
- What type of gas purifiers should you install in your system?
Once the components needed for your system are established, you will need to determine the most appropriate way to configure your gas management system. Figures 1 and 2 are typical configurations: Figure 1 illustrates a system that uses gas generators and Figure 2 shows a system configured for use with high-pressure cylinders.
Figure 1: Gas management system configuration using gas generators.
Figure 2: Gas management system configuration using gas cylinders.
Gas Generators
- Dependable gas supply
- Consistent gas purity
- Safe and economical
Gas generators eliminate the downtime, constant monitoring, and routine maintenance associated with using cylinders. Gas generators produce gas continuously and reliably, without the interruptions that can be experienced during cylinder changes or delays in delivery when using gas cylinders.
A pure and consistent gas supply is needed for reproducible analytical results, but gas purity can vary from cylinder to cylinder in a way that is difficult to control. Dirty or rusted cylinders can also introduce contaminants and particulates into your gas stream. Gas generators eliminate these problems by continuously generating clean and pure gas.
Gas generators are a safe, compact, and virtually maintenance-free source of high-purity gas. Routine maintenance is minimal and since generators don’t store gas at high pressures, they are not as hazardous as gas cylinders. Gas generators can be placed in your lab in close proximity to your instruments, eliminating the need for a remote, isolated storage area. Depending on your specific analytical flow requirements, most gas generators can supply gas to multiple GCs in your lab.
Gas generators are typically less expensive than gas cylinders in the long term. Gas generators offer an unlimited source of high-purity gas, which is available on demand. Cylinders appear to be less expensive initially but, if used continuously, have a significant replacement and resupply cost.
Hydrogen Gas Generators
Hydrogen gas generators produce hydrogen through the electrolysis of water. For operation, these generators require an electrical outlet and a source of deionized water. Restek offers a number of Parker Balston hydrogen generators that can produce flow rates from 100 mL/minute up to 1,300 mL/minute at maximum pressures of 175 psig.
Zero Air Gas Generators
High-purity air is essential as a fuel gas for flame ionization detectors (FID) in order to produce stable, low-level baselines. Zero air gas generators from Parker Balston can turn in-house compressed air into ultra-pure air with less than 0.1 ppm hydrocarbon levels. Varying models are available with flow rates from 1,000 mL/minute up to 30,000 mL/minute at pressures ranging from 40 to 125 psig.
FID Gas Stations
FID gas stations combine a hydrogen generator and zero air generator into one unit. Parker Balston FID gas stations provide both ultra-high purity grade hydrogen gas and zero air for flame ionization detectors. Different models are available and can supply fuel gases for up to six FIDs.
Nitrogen Gas Generators
Nitrogen gas generators produce pure nitrogen from compressed air. Parker Balston nitrogen gas generators produce ultra-pure nitrogen for use as GC carrier gases, make-up gases, and low-flow sample concentrators. Models are available to supply nitrogen at flows from 1 to 75 liters per minute.
Gas Cylinder Accessories
Handling Gas Cylinders
When using high-pressure gas cylinders, there are a number of accessories that should be used in order to safely handle and install cylinders in your gas management system. Dropped gas cylinders are very dangerous and can become flying projectiles if the cylinder valve is damaged. A cylinder holder will safely secure your cylinder to a wall in your lab, preventing it from accidentally toppling over and discharging its contents. Restek also offers protocol wall mounts for gas regulators, tools, and flame arrestors.
Manifolds and Switchover Systems
High-purity automatic switchover systems provide a continuous supply of high-purity gas to your gas management system. Continuous gas supply is achieved by setting the two regulators at slightly different pressures and discharging one side of the system at a time. This allows for the replacement of a depleted gas cylinder without interrupting the gas supply.
Pressure Regulators
The job of a pressure regulator is simple: it reduces the pressure of a gas source to a safe working pressure. However, there are many variables that need to be considered when choosing a pressure regulator. Does your application require a stainless steel or brass regulator? Do you need a single or dual stage regulator? What type of gas are you regulating and what is the desired delivery pressure? Your choice in a pressure regulator will depend on your application and where the regulator will be placed in your gas management system.
Ultra-High Purity Regulators
Restek offers ultra-high purity (UHP) pressure regulators in chrome-plated brass and stainless steel bodies. Both are ideal for applications requiring gas purities of 99.995% or greater, such as those used in carrier and fuel gas supplies. These pressure regulators are made from cold drawn bar stock, which results in smooth, reduced internal dead-volumes, making them ideal for high-purity applications. In situations where corrosive gases are used or where the regulator is in a corrosive environment, stainless steel bodies are required.
Dual-Stage Pressure Regulators
A dual-stage pressure regulator provides more precise pressure control by reducing the gas source pressure to the desired delivery pressure in two steps. They are recommended for supplying gas where constant delivery pressure is critical, especially if your gas source is a high-pressure cylinder. As the cylinder gas is used, the inlet pressure to the regulator from the cylinder decreases. A dual-stage regulator compensates for the decrease and maintains a constant delivery pressure; whereas, a single-stage regulator does not.
Single-Stage Pressure Regulators
A single-stage pressure regulator reduces the pressure of the gas source to the desired delivery pressure in one step. It does not provide the precise control of delivery pressure that can be achieved with a dual-stage pressure regulator. Single-stage pressure regulators should be used for applications where you can monitor and regulate the pressure downstream.
In-Line Regulators
Line regulators are single-stage pressure regulators that are used to provide point-of-use pressure monitoring and control. These pressure regulators are installed directly into gas lines, immediately before your instrumentation, to ensure the appropriate gas pressure is being delivered to your instrument. A dual-stage or single-stage pressure regulator should always be installed upstream of the inline regulator to ensure adequate pressure control.
Pressure Regulator Connections
Restek ultra-high purity pressure regulators come with a variety of different connection fittings for attachment to different high-pressure gas cylinders. In the United States, Compressed Gas Association (CGA) fittings are used and designed for different gas service. In the European Union, German Institute for Standardization (DIN) fittings are used to make these connections, and British Standard (BS) fittings are used in the United Kingdom. Table I indicates the appropriate fitting for each type of gas typically used in setting up your gas management system. We recommend you confirm the fitting needed with your gas cylinder provider prior to ordering fittings.
Table I: Choose fittings for your pressure regulator based on gas type.
|
CGA |
DIN 477 |
BS341 |
|
|
Helium |
580 |
#6 |
#3 |
|
Hydrogen |
350 |
#1 |
#4 |
|
Nitrogen |
580 |
#10 |
#3 |
|
Air |
590 |
#9 |
#3 |
|
Argon |
580 |
#6 |
#3 |
|
P5 (Argon:Methane) |
350 |
#1 |
#4 |
Tubing and Fittings
Precleaned Tubing from Restek
The integrity of a gas management system can be compromised by using tubing that has not been precleaned. Residual dirt, machine oil, and polycyclic aromatic hydrocarbons from the manufacturing process often found in different types of tubing will lead to problems later on. Restek uses proprietary cleaning methods to preclean copper and stainless steel tubing for plumbing your gas management system.
Tubing
Restek offers both stainless steel and copper tubing precleaned and ready to use. The best choice for plumbing your gas management system is stainless steel tubing, which should always be used for hydrogen gas lines. Type 304 stainless steel tubing is the most commonly used variety. Copper tubing is also available and is the most economical choice for plumbing your gas management system.
Fittings
When assembling your gas management system, all of your connections should be metal-to-metal connections. This ensures a leak-free connection, which is important for preventing contaminants from entering the gas stream. O-rings, gaskets, and sealing reagents should be avoided when plumbing your system to avoid contamination of the tubing and gas chromatograph. Swagelok compression fittings are ideal for making your connections, and both stainless steel and brass fittings are offered in ¹⁄₄", ¹⁄₈", and 1⁄₁₆" sizes.
Setting Gas Flows and Checking for Leaks
Once your gas management system is assembled, it should be checked for leaks. Leaks allow moisture, oxygen, and other airborne contaminants to enter your system, as well as accelerating the consumption your gas supply. Detecting leaks with soap-based liquids should be avoided as they can contaminate your gas stream and gas chromatograph. The Restek electronic leak detector is the ideal accessory for inspecting your gas management system for leaks. The Restek leak detector can be used to determine if your system is leaking helium, hydrogen, argon, nitrogen, and carbon dioxide.
Once you have determined that your system is leak-free, you can set your gas flows with the Restek ProFLOW 6000 electronic flowmeter. This flowmeter measures flow from 0.5 mL/min up to 500 mL/min with an accuracy of ± 2% or ± 0.2 mL/min, whichever is greater. The ProFLOW 6000 flowmeter is even Ex rated so that it can be used to measure flow rates of flammable gases, such as hydrogen.
Gas Purifiers
Gas purification is essential in your gas management system. Carrier gases must contain less than 1 ppm of oxygen, water vapor, or any other trace contaminant to prevent column degradation, shortened column lifetime, and increased stationary phase bleed. Contaminants cause ghost peaks to appear during temperature programming and degrade the quality of analytical data. The expense of using high-purity gases in combination with carrier gas purifiers will be offset by longer column lifetime and less instrument maintenance along with better instrument sensitivity. Gas purifiers are available for specific types of contamination (moisture, hydrocarbon, or oxygen) or as a combination of filters that provides broader protection. These purifiers can be installed in-line or using a quick-install baseplate system.
Moisture Removal
Moisture in carrier gas lines will prematurely degrade oxygen and hydrocarbon traps and increase detector noise (particularly with ECDs). As a precaution, you should install a moisture trap before the hydrocarbon and oxygen traps on all carrier gas lines. Moisture traps should also be installed on fuel gas lines, especially if using a gas generator.
Hydrocarbon Removal
Use a hydrocarbon trap if your gas has a potential source of hydrocarbon contaminants (e.g., an oil pump in an air compressor) or if you suspect you are observing carrier gas ghost peaks. Install the hydrocarbon trap after the moisture trap to prevent moisture from degrading the hydrocarbon-trapping ability of the activated carbon in the hydrocarbon trap.
Oxygen Removal
Oxygen is a GC column killer and it can enter the system at any connection that is leaking. Because oxygen can enter a gas line at any fitting, the oxygen trap should be the last connection before the gas line enters the chromatograph. Oxygen traps should only be used to clean fuel and carrier gas streams with very low moisture content because water can react with the oxygen trapping and indicating media. They are recommended for use with high-purity gas cylinders and palladium-purified hydrogen generators (H2PEMPD). Palladium purification lowers oxygen and moisture concentrations in the hydrogen gas to levels compatible with oxygen traps. Oxygen traps should not be used with PEM hydrogen generators because they lack palladium purification and, thus, the hydrogen gas they produce through the electrolysis of water can contain a high concentration (percent levels) of water. Oxygen traps (including triple filters) are not suitable for gas streams with moisture concentrations greater than part-per-million levels and damage can result if they are used under high moisture conditions. In addition, oxygen traps should never be used on air gas lines.
Leak Checking
To prevent column degradation, increase column lifetime, and decrease stationary phase bleed, carrier gas supply lines need to be leak-free to prevent the introduction of oxygen. This can be monitored by frequently leak checking all carrier gas system connections using the Restek electronic leak detector.
Rely on Restek for Gas Management
An effective gas management system is essential to obtaining accurate, reliable GC results. Restek offers the products and expertise to help you set up and maintain the right system for your lab. Whether you use gas generators or freestanding cylinders, we have the equipment you need to ensure a reliable, high-purity gas stream to your GC instruments.