Pursuing purity

Ultra high purity gases are increasingly used in Gas Chromatography across a wide range of industry sectors. But why does purity matter so much and is the higher cost of these premium gases justified?

Demand for ultra pure gases for use in gas analysis has soared since the development of Gas Chromatography (GC) in the 1950s. An increasingly divergent range of industries began to use analytical techniques to analyse samples for a wide range of applications, including as a means of quality control during production processes. Today, GC is regarded as intrinsically critical to the production of most processed goods including pharmaceutical drugs, petrochemicals and food products.

As part of their focus on quality, industrial manufacturers have increasingly been using gas analysis to detect and quantify the presence of more components, at much lower concentrations and to a much higher level of accuracy than ever before. As a result, global demand for ultra high purity gases continues to expand rapidly.

Ultra high purity gases are commonly used as a carrier gas, which is used in GC to carry the sample gas through the column so its composition can be determined. A detector sends an electrical signal to a data handling station, which in turn produces a chromatogram showing a series of peaks – each denoting and quantifying a different gas component. In Europe, the most popular carrier gas is helium but other common carrier gases include nitrogen, hydrogen and occasionally argon. Gas purity is vital in GC because critical contaminants such as oxygen, water and hydrocarbons can affect the accuracy of the measurements produced by causing baseline noise, column degradation and adversely affecting the operation of detectors.

While methods of detection can vary according to the application and the nature of the component gases being analysed, the basic principles of operation of the gas chromatograph have changed comparatively little over the years. However, the technology used in GC has continued to evolve and is much more sophisticated in terms of its capabilities. Column technology has also advanced significantly but replacements of these hi-tech components represent a significant on cost, which can quickly mount up in a laboratory that may be operating multiple gas chromatographs.

The first sign that a gas chromatograph is not functioning perfectly is a steady deterioration in the quality of the analytical results. Peaks become less sharp and baseline noise can also become a problem. For the analyst this indicates that the column may need replacing, usually due to impurities in the carrier gas attacking the column. As well as the obvious cost implications, changing the column causes downtime, which has a knock-on effect on productivity.

In a bid to ensure highly accurate analytical results, at the same time as extending the life of columns and minimising downtime, laboratory managers have increasingly chosen to upgrade the quality of the carrier gases they use. For many, the cost savings and accuracy improvements achieved by using higher grade gases are considerable. For example, a laboratory Air Products has been working with recently had been finding that they needed to replace the column in their gas chromatograph every 24-45 days, depending on the nature of the gas sample being tested. This was costing the company a significant amount of money in column costs as well as affecting the accuracy of their analytical results. By switching to ultra high purity gases, featuring Air Products’ proprietary BIP technology, which ensure a high degree of purity at the point of use, the need for column exchange reduced significantly to every 80-104 days. Air Products has recently extended its range of ultra high purity gases, to include hydrogen BIP, in a bid to further improve the analytical accuracy of GC for a wide variety of value-added industrial applications.

This hydrogen BIP technology delivers an exceptional ultra high purity gas product, with dramatically reduced levels of key impurities such as oxygen, water and hydrocarbons compared to conventional hydrogen grades. Fitted with an internal purifier and a unique patented valve system, the technology ensures that the gas consistently meets the highest standard of purity at the point of use. For the laboratory analyst, using this new gas product can significantly reduce lower detection limits and provide an assurance of improved accuracy at the same time as extending the life of the column.

Hydrogen is not new to GC and it has been used in the pharmaceutical industry as both as a carrier gas in a wide range of GC applications and as a detector fuel gas for FID, NPD and FPD for decades. Modern highly-sensitive methods of detection are capable of giving accurate readings for even the most complex samples. This kind of gas analysis is performed at each stage of the production process.

The arrival of ultra high purity BIP hydrogen may present some analysts with an opportunity to further improve analytical accuracy and potentially deliver analytical results more quickly by using hydrogen as a carrier gas. However, helium is expected to remain the carrier gas of choice for the vast majority of users, mainly because it is totally inert and also produces analytical results rapidly and with high accuracy.

In a bid to bring about further improvements and to meet industry needs, research and development work is continuing, exploring ways to make laboratory gases even easier to use as well as maximising their quality and reliability. Complementary technologies can also be used to meet more unusual user demands where cylinder supply is difficult or impossible. For example, when asked to provide a carrier gas for a gas chromatograph being used to test samples in the Amazonian Rain Forest, a compact generator was supplied to deliver the hydrogen, reliably and efficiently onsite.

Pursuing gas purity is likely to remain a key focus for gas suppliers in the future as laboratories increasingly look for higher specification products that can deliver benefits in terms of accuracy, cost-efficiency and reliability.