Many applications require very high purity, inert gases to blanket hazardous chemicals or as protective atmospheres. The electronics and semiconductor industries use ultra-high purity specialty gases as part of the production process for each of these applications, there are several contaminants that need to be controlled at the point of production, during transport and storage as well as the point of use. We offer a full suite of sensors, instruments, and complete analyzer systems capable of detecting all trace impurities in gases down to low parts per trillion.
We offer the following measurands:
Moisture is the most common contaminant that needs to be removed, but, because it is so prevalent in the atmosphere, simply drying the gas during manufacture is not always enough. The ultra-high purity gas must also be checked for trace moisture after storage and tool downtime, as well as regularly at points in the process to ensure moisture has not found its way back in.
The presence of trace oxygen in gas is often a good indication of leaks in the system. In the case of UHP nitrogen and argon, small traces of O2 may be present after the cryogenic air separation process.
In complex specialty gases it’s often necessary to detect traces of several contaminants ranging from traces of gases (eg oxygen, nitrogen, helium) as well as traces of oil and other hydrocarbons. UHP O2, N2 and Ar also may be contaminated with trace hydrocarbons after processing and storage.
This article describes the solutions available for ensuring the quality of UHP gases and looks at the best practices for sampling.
The purity of gases required vary from application to application. In the table below we have listed some typical purities for gases by application:
| Gas Type | Purity | Maxmium moisture content |
| R744 Refrigerant Grade CO2 | 99.9% | < 10ppm |
| Synthetic Air | 99.99% | ≤ 5ppm |
| High Purity Nitrogen | 99.999% | ≤ 3ppm |
| High Purity Argon | 99.9995% | ≤ 0.5ppm |
| Neon | 99.996% | <1ppm |
| Krypton | 99.999% | <3ppm |
| Xenon | 99.9995% | <0.1ppm |
| Oxygen | 99.98% | < 5ppm |
| Hydrogen | 99.999% | < 1ppm |
| Helium | 99.999% | <5 ppm |
| Octafluorocyclobutane (C4F8) | 99.999% | 1 ppm |
| Difluoromethane (CH2F2) | 99.995% | 2 ppm |
| Tetrafluoromethane | 99.999% | 1 ppm |
Not all moisture sensors are capable of measuring trace moisture down to the very low parts per billion needed for UHP gas quality. We are unique in our offering of a range of trace moisture measurement technologies to suit the needs of varying applications and budgets.
| Technology | Benefits | Is it for me? |
| Ceramic Metal Oxide Moisture Sensor |
Our sensors have been developed especially for these high purity applications providing measurements down to low parts per billion. Historically proven as a suitable measurement technology with the benefit of being easy to install and maintain. Highly cost-effective. |
These small sensors are easy to install and maintain, making them a cost-effective option. Typical installation is on UHP feed gas supplies to manufacturing tools. |
| Chilled Mirror | Provides highly accurate, fundamental measurements of dew point with minimal drift. Capable of providing moisture content readings down to parts per billion. | For measurements of dew-point, Chilled Mirror Hygrometers provide the greatest accuracy and reliability. As a premium product, they are often used by gas manufactures as a standard during production for quality control. |
| Quartz Crystal Microbalance | Provides fast, precise measurements of moisture content down to 100 ppbV. | Another premium product, QCM analyzers require minimal maintenance. If the main interest is for moisture content rather the dew point temperature, then QCM technology is a good choice. |
Suggested instruments for moisture measurements in UHP gases:
Provides highly accurate and repeatable measurements of frost-point down to –90 °C with minimal drift. Often used in semi-conductor manufacture where precise control of moisture in essential.
The latest addition to the S8000 range has the capability to measure frost points down to –100 °C, with no need for external cooling.
Using the latest developments in quartz crystal microbalance technology, the QMA401 measures moisture content from 0.1 ppmV to 2000 ppmV with a fast response in both dry to wet and wet to dry transitions. It requires minimal maintenance and offers a low lifetime cost.
Learn more about QMA401.| Technology | Benefits | Is it for me? |
| Galvanic Electrochemical | These sensors are small, easy to use, install and are highly cost-effective. Key benefits include low power consumption and the ability to use air as a calibration gas. They are accurate for measurements of trace oxygen from 0-10 ppm. | Electrochemical sensors are chemically resistant and can be used when trace hydrocarbons are present. |
| Zirconium Oxide | These solid-state, non-depleting sensors are suitable for a wide range of trace O2 applications. They provide reliable and stable measurements in the range of 0-10 ppm. | The sensors are non-depleting, with a service life of between 3 to 5 years, making the cost of ownership low. |
Suggested instruments for trace oxygen measurements in UHP gases:
Based on AII’s high-performance galvanic oxygen sensors, the GPR-1600 has a lower detection limit of 50 ppb O2. It offers a typical sensor lifetime of around 24 months to keep cost of ownership and maintenance to a minimum.
Designed to measure trace oxygen in inert gases such as nitrogen, carbon dioxide, helium an argon, the XZR400 features a fast-responding zirconium oxide sensor. With a lower detection limit of 100 ppb, it is suitable for a range gas purity applications.
Learn more about XZR400| Technology | Benefits | Is it for me? |
| Plasma Emission Detector (PED) | Used in conjunction with gas chromatograph systems, these detectors allow a wide range of gases and trace impurities to be detected in very low parts per billion. | PED technology can be configured to detect a wide range of impurities in backgrounds of Ar or He. The detector must be used in conjunction with a gas chromatograph system. |
| Flame Ionisation Detector (FID) | Detects hydrocarbon gas concentration as part of a gas chromatograph system. Lower detection limits of low parts per million are possible. | FIDs respond to all hydrocarbon gases, including methane. The detector must be used as part of a gas chromatograph system. |
Suggested instruments based on PED and FID technology:
This modular process GC combines the functionality of two GCs in one. As well as offering users the option to use PED, FID and TCD detectors, dedicated moisture and oxygen sensors can also be integrated.
The LD8000 MultiGas is an online gas analyzer to monitor trace N2, O2, H2O, CnHm in Helium. The compact 4U unit has been designed to meet the requirements of the Helium cryogenic installations for online measurement.
Learn more about LD8000 MultiGas
Using the FID, LD2000 offers users a complete solution for monitoring UHP bulk gases to detect trace hydrocarbons. Easy to install with a small footprint.
| Technology | Benefits | Is it for me? |
| Thermal Conductivity Sensor | This technology is used to measure the purity of the gas itself, rather than moisture content. ie. oxygen in Nitrogen or Argon in Nitrogen | Choose this technology if determining the purity of the gas itself is the main concern, rather than looking for moisture content. Thermal Conductivity analyzers can be used to quickly discover leaks of air into a system and are often used as part of quality assurance during manufacture. The larger the difference between the thermal conductivity of the gas of interest and the background gases, the low the limit of detection. |
| Thermal Conductivity Detector (TCD) | Used in conjunction with a process GC, the TCD allows measurements from % to ppm in binary gas mixtures |
The type of sensor or analyzer is only one part of the equation when it comes to making accurate measurements of moisture or other trace impurities in high purity gas: the materials and components in the sampling system play a vital role. Choosing unsuitable materials or failing to provide adequate sample condition will greatly affect the reliability of the measurements.
Control over the flow of gas and stream selection are especially crucial for process gas chromatographs and online trace impurities analyzers. LDetek offer a wide selection of traps, pressure regulators and gas purifiers for use with their own analyzers and other ranges.
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