Improving LC-MS Separations with On-Site Nitrogen Generation

Interview conducted by Jake WilkinsonJun 20 2016

LC-MS is a highly powerful analytical technique that combines the exceptional separation power of liquid chromatography with mass spectrometry, a highly sensitive chemical identification technique. As a result LC-MS can be used to determine the constituents of complex chemical mixtures and this capability means LC-MS systems are found in most advanced chemical and life sciences laboratories. In order to function LC-MS systems needs a nitrogen supply, which can be either static (in the form of cylinders or dewars) or dynamically generated on site.

AZoM spoke to Greg Stringfellow, of Peak Scientific, about how their on-site nitrogen generators can be used to improve the quality and efficiency of LC-MS separations whilst also saving laboratories money in the long term.

What is the role of Nitrogen in LC-MS (Liquid Chromatography - Mass Spectrometry)?

Nitrogen is typically used to effectively eliminate the solvent of a sample in order to prevent it passing through from the ion source to the quadrupole and the detector.

Solvent removal is essential to maximize the sensitivity of an analysis and to prevent any erroneous results.

What mass spectrometry ionization methods are used in conjunction with Nitrogen?

Nitrogen is used in different ways depending on which ionization method is employed.

In electrospray ionization (ESI) detectors, nitrogen is used as a nebulizer gas to produce a mist of charged droplets which results in the separation of the solvent and the ionized sample. The ionized sample then passes through to the quadrupole(s) and to the detector.

In atmospheric pressure ionization (API) detectors, nitrogen is used to spray the sample solution into a heater where ionization occurs.

In other systems, nitrogen can be used as a ‘curtain gas’ to facilitate the separation of sample and solvent ions and to prevent passage of solvent into the vacuum chamber of the mass spec.

As you can see, nitrogen is essential for a range of LC-MS applications!

A view down the path charged analytes travel in a mass spectrometer. The quadrupole that separates the analytes in order of their mass can be seen in the distance. Jens Goepfert | shutterstock.com

How important is the purity of the nitrogen used for LC-MS separations? What control do researchers have over this?  

All of Peak’s generators have been tested and approved by each of the major instrument manufacturers to ensure that excellent results are obtained by our customers. Depending on which system requires nitrogen, we have a number of tailored solutions to provide the right quality of gas that will ensure the best results.

In LC-MS, most applications recommend 95% pure nitrogen because oxygen, which makes up the remaining 5% of the gas, has not been found to be detrimental to analysis when supplied by a gas generator.

When developing nitrogen generators in close cooperation with LC-MS manufacturers, we have found that contaminants, such as phthalates and butylated hydroxytoluene (BHT) have significantly more impact on the quality of the analysis results than O₂ content. As a result of this we take great care to only include high quality components which are phthalate and BHT free in the design of our products.

Peak Scientific supply a range of nitrogen generators which can be directly integrated into LC-MS systems.

How does on-site gas generation impact lab workflows?

Having a gas generator in place ensures that that Lab Managers and staff can focus fully on their analysis as they will not need to monitor gas levels in cylinders. Instead, the gas is supplied on demand from Peak’s generators, as and when it is required.

Furthermore, from time to time customers can experience supply issues or delays with cylinders which can have a consequential impact on the turn-around time of samples, delaying important research. A Peak gas generator will eradicate these possibilities ensuring maximum efficiency at all times.

In addition to this, LC-MS typically require more than 20 L of nitrogen per minute. For a typical 8 hour working day this can equate to 9,600 L of nitrogen. This is a significant volume of gas, which would mean replacement of a cylinder per day. This is not just cumbersome, but also comparatively expensive. The return on an investment for a LC-MS nitrogen generator is typically around 12 months depending on the level of LC-MS usage and the nitrogen model purchased.

Are there any analytical advantages of using nitrogen that is generated on-site over nitrogen stored in a cylinders or dewars?

With a Peak generator you will have consistency in your results, whereas with cylinders this is not always entirely the case as impurities in the gas can vary from cylinder to cylinder. Also, cylinders require to be changed periodically and this can allow air and impurities to be introduced to the analytical system which can have an impact on results if not purged out fully prior to running samples. These impurities can harm the quality of data from LC-MS experiments.

Furthermore, when you consider the safety advantages of a generator which only generates gas on demand versus a cylinder or dewar that stores massive amounts of Nitrogen gas which can very quickly cause an asphyxiating atmosphere in the event of a leak, then this makes generators a popular choice for LC-MS users.

What options for LC-MS nitrogen generation do Peak Scientific offer and in what type of lab is each system most suitable?

Peak works alongside all the major manufacturers of LC-MS systems to ensure that we have gas solutions that meet the requirements of all their instruments. Many have different gas flow requirements, and some need not only N₂ but also dry air, and Peak can provide solutions for them all.

Our portfolio is vast and we have solutions for single and multiple LC-MS systems. We can also provide generators with or without internal compressors, depending on whether the customer has their own suitable in-house air supply.

The list of industries that use LC-MS in their labs is extensive and each of their gas requirements will be unique dependent on the factors just mentioned, but Peak will have a solution for all their needs.

The Genius NM32LA is one of the most popular nitrogen gas generators in Peak Scientific's extensive portfolio.

What impact does on-site gas generation have on the environment?

We see generators as being far more environmentally friendly than cylinders and customers who make the switch-over are reducing their carbon footprint. Yes, generators require a power supply to operate, however Peak’s engineers have ensured that they are as efficient as can possibly be. Only one delivery is required for the generator, whereas many customers have regular drop-off’s from cylinder trucks, which has a huge impact on the environment as does the purification and compression processes for cylinder gas.

To put it into perspective, a Peak nitrogen generator supplying 32 liters per minute of nitrogen to an LC-MS will produce over 9.5 million liters of nitrogen before needing to be serviced. This volume of gas is equivalent to over 1000 nitrogen cylinders, all which need to be transported to the customer site, usually on a weekly or monthly basis.

Peak has developed all reasonable ‘due diligence’ controls to ensure that our products comply with the principles and requirements of the European RoHS (Restriction of Hazardous Substances) Directive 2011/65/EU. Similar directives in the United States and China, for example, have also been captured within this program. Peak also fully complies with its obligations towards the European WEEE (Waste of Electrical and Electronic Equipment) Directive 2012/19/EU.

Where can our readers find out more about how on-site gas generation could benefit their lab?

More information about Peak and our products can be found on our website which contains a “Learn” section that includes informative application notes, user stories and testimonials.

You will also find information on our gas generators for GC, TOC, FTIR and many other applications within. We are more than happy to answer any questions that you may have regarding our products, just call one of our offices worldwide.

About Greg Stringfellow

Greg Stringfellow is a Product Manager at Peak Scientific, and has been with the company for 5 years.

Greg studied business at the University of Strathclyde before working with distributors globally in the gas detection market for a number of years with GMI in Inchinnan, then the food safety market thereafter with Neogen Europe.

When Greg moved to Peak he was entrusted with the role of Gulf Regional Sales Manager, tasked with building relationships with distributors in the Middle East.

His roles have developed throughout his time at Peak and is now proud to be part of their Product Management team.