There’s something in the air
14 Feb 2013 by Evoluted New Media
It may not be something you have thought of before – but have you ever wondered where the specialty gases that are used in your laboratory every day come from? Calibration gas mixtures used for calibrating analytical instruments such as gas chromatographs and continuous emissions monitoring systems are blended to very high accuracy and typically come with ultra-low levels of critical impurities resulting in more consistent and accurate analyses.
Creating each gas mixture starts by sourcing the necessary raw materials – the gas components. Air Products owns and operates over 300 air separation plants in more than 40 countries that extract the nitrogen, oxygen and argon from atmospheric air. The air is liquefied down to cryogenic temperatures of around –196oC. The liquid air is then distilled in a column, which separates the air into pure nitrogen, oxygen and argon – these can then be shipped as a cryogenic liquid to one of the European specialty gas mixing plants in Keumiee in Belgium, Sant Celoni in Spain or Worcester, UK.
Many ultra-high purity gases such as hydrogen, carbon monoxide and helium are produced by Air Products using a variety of technologies. For example, helium is extracted from certain natural gas sources. The helium is formed as a result of the radioactive decay of many heavy elements, such as uranium and thorium. High concentrations of helium are sometimes found in natural gas reserves, when they are capped with impermeable rock that traps the helium. More unusual and exotic gas components are sourced from an extensive global network of specialist suppliers. In total almost 400 gas components are used to produce an enormous range of calibration mixtures for a wide range of analytical applications.
Designed to order for each analytical application, it is not unusual for these calibration mixtures to contain 30 or 40 gas components, and in some instances many more. Making these high-specification mixtures, using precise quantities of many different gases, is not an easy task and requires a great deal of skill and knowledge to ensure the product is blended to ensure a high level of accuracy and stability.
In the drive for accuracy, a growing number of pharmaceutical, petrochemical and other companies now require calibration mixtures that are certified by an ISO 17025 accredited laboratory and an ever wider range of such products are becoming available.
During production, a variety of tried and tested cylinder filling techniques and cylinder treatments are used to ensure that each gas mixture is accurate, highly stable and of a consistently high quality. These techniques have been developed based on years of experience in the production and supply of ultra-high purity gases and calibration mixtures and draw on detailed knowledge about how individual gas components behave, at varying pressures and in different combinations. By applying the right cylinder treatment and using the appropriate filling technique - the stability and shelf life of a gas mixture can be significantly improved. Specialist filling techniques are used for calibration mixtures at ppb or even ppt concentrations or when making mixtures containing highly reactive compounds, where long-term stability is critical but difficult to achieve.
For many pure gases used in laboratories, advances in cylinder technology have meant that external purification is no longer necessary to guarantee a consistently high standard of purity. In particular, Air Products’ BIP technology is providing gases with less than 10 ppb oxygen and less than 20 ppb moisture from the first to the last molecule in the cylinder. This obviously removes a significant hassle factor for the operator by eliminating the need for any external purification equipment – potential leaks are eliminated and no maintenance is required.
Next time you calibrate your analytical equipment, spare a thought for the care and attention involved in developing a gas product that meets your requirements and helps you to deliver accurate measurements every time.
By Gary Yates, Air Products’ European Product Manager Analytical and Laboratories
