IS THAT "LABORATORY EQUIPMENT" REALLY SUITABLE FOR ANALYTICAL GAS APPLICATIONS?
Critical laboratory and environmental applications across various industries rely heavily on high purity gases to ensure the accuracy and reliability of analytical results. Contaminants like moisture, oxygen, and hydrocarbons, found in all gases, can compromise the integrity and validity of analytical results. Because different analytical techniques have varying sensitivities to impurities, the first step to ensuring the integrity of analytical outcomes is selecting the appropriate high purity gas for the specific application. Based on the concentration of contaminants, high purity gases are classified by grade and expressed using a “number of nines” in the purity percentage. For example, grade 4.0 gases are 99.99% pure and contain up to 0.01% possible impurities (can include oxygen, moisture, hydrocarbons, and other trace gases). Grade 5.0 
gases are 99.999% pure, containing up to 0.001% possible impurities, and so on (Table 1). By clearly indicating the amount of allowable impurities, this grading system simplifies choosing the right gas for various scientific, medical, and research applications. While ensuring the high purity gas meets the required purity standards of a specific analytical application minimizes the risk of impurities affecting sensitive analytical outcomes, it is only the first step. Common contaminants, naturally present in ambient air, can be introduced into the gas stream at any time by the gas delivery equipment or any of its components.
Materials and Design
Atmospheric contaminants can enter a high purity gas system through leaks, diffusion, or adhesion onto the surfaces of the gas delivery equipment. To this end, the gas delivery equipment used in analytical applications, such as pressure regulators and flow control valves, must be carefully selected. Materials of construction must be compatible with specific high purity gases to avoid adverse reactions or interactions that could compromise the purity of the system. Inert materials like stainless steel and PTFE are preferable to elastomers and highly reactive carbon steel. From inlet to outlet, high-quality construction and precise design features, such as smooth internal surfaces and leak-tight connections, are essential to preserve the purity level of the gas and ensure the success of critical analytical applications.
Pressure regulators constructed with machined brass or 316L stainless steel barstock components are preferable for analytical applications over regulators constructed with forged metal components. Machining a regulator body from a solid bar of cold-drawn metal creates a small internal cavity in the regulator body. The cold-drawing process produces barstock with a very tight grain structure, which prevents the regulator’s internal surfaces from adsorbing impurities. The low internal volume and the tight grain structure make purging contaminants like moisture and oxygen easier. The machining process also results in a surface finish with a very low roughness average (Ra) and a lower wetted surface area. This finish helps to decrease particle shedding and minimize the total area exposed to gases, which lessens the potential for contaminating a high purity gas stream. The robust construction and improved reliability of machined barstock bodies make them a superior choice for high purity regulators and flow control valves, ensuring consistent performance in critical analytical applications.
Pressure regulators and flow control valves used in analytical laboratory applications should have diaphragms made from metals that effectively prevent contamination. Many elastomers, when exposed to high temperatures, release volatile organic compounds (VOCs) and other gases, a process known as "off-gassing." Thus, diaphragms constructed from elastomers such as EPDM, chloroprene, or nitrile are naturally prone to off-gassing when heated by the temperature of the gas or due to flexing of the diaphragm. Additionally, a regulator or control valve is exposed to ambient air each time it gets removed to switch out the gas cylinder. Elastomer diaphragms will absorb moisture and other contaminants from the air. When reconnected, these contaminants are released and eventually enter the gas system. For high purity laboratory applications, 316L stainless steel is the preferred diaphragm material. Stainless steel diaphragms provide excellent resistance to corrosion and chemical reactions compared to those constructed from elastomers. They also offer a lifespan exceeding 10,000 cycles, ensuring reliable performance without introducing contaminants.
Some regulator and control valve designs incorporate a 316L stainless steel diaphragm lined with an elastomer. Although the diaphragm is stainless steel, the seal is created between the regulator body and the elastomer liner. Like an elastomer diaphragm, an elastomer liner absorbs moisture and contaminants, which can diffuse through the material and contaminate the gas stream. Elastomer liners may not be compatible with certain gases and will degrade over time. A poor seal between the body of the regulator and the diaphragm creates a leakage point through which contaminants will enter the system. A 316L stainless steel diaphragm with a metal-to-metal seal (metal regulator body sealing to a metal diaphragm) is the most reliable, leak-free diaphragm construction for any pressure-holding device in a high purity gas system.
Helium Leak Integrity
The leak integrity of any device can be described by the rate at which helium, a tiny inert atom, penetrates its seals. A mass spectrometer is used to measure helium leak integrity in a process known as helium leak detection. The leak rate is expressed in standard cubic centimeters (scc) per second (sec). For example, a pressure regulator with a helium leak integrity rating of 1 × 10⁻⁸ scc/sec, the minimum for most high purity applications, allows the volume of a cubic centimeter of helium (He) to escape in approximately 3.1 years. A helium leak integrity rating of 1 × 10⁻⁹ scc /sec means it takes ten times longer, or 31 years, for the same volume of gas to escape. Higher helium leak integrity minimizes the risk of gas leaking out of the regulator, thus preventing external contaminants from diffusing into the system. Furthermore, when gas is in flow conditions, a higher helium leak integrity rating mitigates the phenomenon known as the Venturi effect. In the context of pressure-reducing devices, the Venturi effect is the pressure drop that occurs as gas flows through a narrowed passage. This pressure drop potentially creates a suction effect, which can draw in contaminants from the surrounding environment. By preventing the infiltration of external contaminants, the integrity of a high purity gas stream is preserved, ensuring reliable and accurate performance in those sensitive analytical applications where gas purity is paramount.
It is important to remember that not all high purity regulators are created equal. Regulators designed for high purity applications are more costly than regulators intended for general-purpose use. Due to the high amount of machining involved, barstock bodies are more expensive to manufacture than forged bodies, and stainless steel diaphragms and seals cost more than elastomers. High-quality materials and precision manufacturing influence helium leak integrity, a crucial factor for preventing system leakage. Be wary of so-called “laboratory-grade” equipment that does not feature a helium leak integrity rating suitable for analytical applications. Similarly, although a device may contain high purity regulators, it is not necessarily high purity equipment. Any device suitable for high purity applications must have a helium leak rating of 1 × 10⁻⁸ scc/sec or better for the device as a whole. When in doubt, insist on a device-specific helium leak certification. While often a nominal extra charge, the cost is quickly recovered when compared to the application expense from inadequate equipment.
CONCOA high purity pressure regulators, control valves, and manifold switchovers are engineered to support the stringent demands of critical laboratory applications. All CONCOA high purity devices are designed for at least a 1 × 10⁻⁸ scc/sec helium leak rate and each assembly is leak-checked with helium using a mass spectrometer before it leaves the factory. Based on application requirements, CONCOA high purity gas controls and systems are offered in brass, chrome-plated brass, or 316L stainless steel barstock, with 316L stainless steel diaphragms and metal-to-metal seals. CONCOA 300 Series regulators feature a leak integrity rating of 1 × 10⁻⁸ scc/sec, while 400 Series regulators boast a leak integrity rating of 1 × 10⁻⁹ scc/sec. For laboratory applications requiring a continuous supply of high purity gas without pressure fluctuations, CONCOA offers a variety of manifold switchovers in 316L stainless steel or brass, featuring a helium leak integrity rating of 1 × 10⁻⁸ scc/sec. The 526 or 527 Series pressure differential switchovers can be used with one cylinder per side or with a manifold header for increased storage capacity. If higher levels of automation are required, CONCOA’s AutoSwitch 2 provides fully automatic priority assignment from high pressure cylinder sources for lights-out operations. For cryogenic liquid supply systems, CONCOA’s IntelliSwitch II is a reliable and cost-effective solution that provides fully automatic switchover using liquid cylinder primary and high pressure or liquid cylinder reserves. Finally, if analytical applications require chemical inertness, CONCOA’s SilcoNert® 2000 pressure differential switchover is available. By ensuring high-quality construction, precision manufacturing, and minimal leakage, CONCOA pressure regulators, control valves, and automatic manifold switchovers preserve the high purity levels of gases required to support critical laboratory applications in technology, healthcare, and scientific research.