“Where is my helium tank? I thought we had a few coming in this week.” This was a colleague of mine in April when he was at 500psi left on his helium tank before starting a project.
While we should have all expected this to happen at some point, I don’t know that most operators were prepared for this helium rationing to come on so swiftly. Like many out there, manufacturers are also being hit with a ‘force majeure’ from gas suppliers unable to meet supply requests. Let’s discuss how to potentially keep the lab going. This is going to be broken into two main parts; first we are going to go over those that cannot switch to an alternative gas and the second will be pointers on how to switch over to an alternative gas.
Part 1: I can’t switch to an alternative gas, what can I do to help get through?
Before starting, please be aware that contacting the GC instrument manufacturer is a must if questions about the system arise. As a manufacturer of gas chromatography instruments, there are a few systems, I’m sorry to say, CANNOT be converted over to alternative gases based on design or system requirements. An example of this would be the Shimadzu BID-2030 (barrier discharge ionization detector); it requires helium and there is no alternative gas that can be used. In situations like this or those where the method is unable to be adjusted, saving as much gas where you are able is key. There are a few questions users should consider:
- Are their parameters within my current method that could be optimized?
- How much am I really running the system and what is the turnaround needed?
- Are there finances available to purchase items to help in the rationing of gas?
First, consider the method parameters being used. Are there things that could change without affecting the sample? Is it possible to adjust the split flow after your sample has made it to the column? For example, in a splitless injection after the sampling time, the split flow might be set higher than necessary. Consider if that flow could be lowered; keep in mind, some of this will be dependent on samples being run. For those running a split injection with a high split flow, does it make sense to hold that high split flow for the whole run? It may be possible to lower it sometime after injection. Another simple adjustment would be to use an alternative makeup gas. If you are using helium as a makeup gas for a detector like FID (flame ionization detector), you may be able to convert to another gas like nitrogen with no noticeable change to sensitivity.
If optimization of the method is not an option for the lab, consider how much the system needs to be at operating conditions. If no one ever runs samples on the weekend, maybe it is time to come up with a weekend soft shutdown/standby. Depending on the detectors, it might be worth reviewing if a daily standby can be used too. The key is to make a method that requires the least amount of gas used (which may require turning down temperatures) and has the fastest turnaround time for the needs of the lab. An example of a simple standby method would be lowering the column oven to room temperature with a minimal flow through the column. A method like this can easily be added as a last line in any sample sequence, so the system goes into this standby at the end of the batch.
The trick to the standby method is figuring how long your system takes to get back to a ready state. We can also build a method that brings all possible temperatures down to room temperature and then bring the gas flows to the lowest allowable level. Understanding how long your system takes to come to ready from cold is key! While you may think that temperature is going to take the longest to come back to original settings, it’s almost always how long the detector takes to stabilize that determines when a system is ready. For example, something like an FID can be ready from cold in about 30 min whereas an ECD (electron capture detector) could take up to a day to stabilize. Each detector has its own needs and requirements for turnaround. Typically, this type of soft-shutdown method works best for weekends or more than a few days where the system will not be utilized, but needs to be able to come ready with some speed. In these situations, the detector will need turned off (i.e., extinguish the FID flame, turn of the ECD current), the heat to all of the heated zones turned to room temperature, and flow lowered so that the minimum is being used. I like 40°C, personally, because the system can still control the temperature, but it is low enough to not damage the system. I also use less than 1mL/min column flow with a very low split flow. Depending on the detector gases used, you can lower or potentially shut off the gases. This works well because the gas flow through the system keeps the unit on with gas flowing but is using the least amount of gas because the temperatures are low. For extended periods of time, a full shutdown might be OK.
One thing I would NOT recommend is shutting down your GC or GC-MS systems every night. These systems are meant to be left on; however, no one ever said they had to be at method operation parameters. Consider coming up with a standby method or soft shutdown that meets your laboratory needs. Also, contact your system manufacturer; with new systems, many manufacturers are building standby functions into their systems and software to make this process simpler than ever before!
The final option for conservation is going to require financial means and a call to your instrument manufacturer. In some cases, manufacturers have optional assemblies that can be added to existing units that can help save on gas. An example would be something that allows you to select the gas being used on the system. An optional item like this can run an analytical gas (helium) and then switch to a standby gas (like nitrogen or hydrogen) when the system is not needing to be operational. There are other tools like this that can help you if you are truly stuck using helium gas for your GC system.
While it may seem impossible to continue to use helium with this rationing going on, there are ways to make it work. Within my lab, we use a combination of all of these tricks for systems like the BID-2030 mentioned above to accomplish the projects we need to work on. It’s not always easy, but there are ways to minimize the anxiety of when will the next cylinder of helium show up.
Part 2: I’m not restricted to my carrier gas; how do I switch?
Before starting, please be aware that contacting the GC instrument manufacturer is a must if questions about converting to alternative gases arise. Once the lab has confirmed that it is OK to change to an alternative gas there are a few things the need to be considered:
- What are my gas options?
- Am I worried about sensitivity?
- Is it important to keep the method as close to the current one or should I optimize it?
- My company is worried about the safety of switching to hydrogen, what should I do?
The first question most ask is, what gases can be used? Typically for GC, many users switch to hydrogen, nitrogen, or in some cases argon. Helium is by far the best from an overall use standpoint, but hydrogen is a close second when it comes to pros for use. The first hurdle to picking an alternative gas is understanding the pros and cons of use. Hydrogen can speed up an analysis, but in many cases cannot be used as a detector makeup gas. Nitrogen and argon are typically less expensive as far as gases go, but they see longer run times and less sensitivity. Hydrogen and nitrogen also have an advantage in that generators can be used instead of tanks. It is possible that when switching to an alternative carrier gas, the manufacturer may recommend a second alternative detector makeup gas. Many of these factors need to be considered when starting the search for the alternative gas.
The next challenge when talking about converting is understanding that there will be a change in sensitivity and not for the better. There is a reason many applications are on helium; it gives the best sensitivity. While that is true, users need to look at their individual methods to determine how much sensitivity is required for the analysis they are running. For example, on GC-MS, if I know that I can do with about half of the sensitivity I have now then I can easily switch to hydrogen. Each GC detector (including MS) has a different loss of sensitivity when you change the gas. If sensitivity is of no concern or there is a level of loss that can be handled, the system will require a slight method change.
While it may seem scary, changing to an alternative carrier gas is simple. You can just change the gas and let the method parameters adjust themselves in the software. This will in no way optimize your system nor is it guaranteed to give the best-looking chromatography. Luckily, there are numerous programs out there like the Restek EZGC Method Translator1 to help take the guesswork out of updating a method. In programs like this one, users input the carrier gas type and basic parameters for what is currently set in the method and the system then does the calculations on the backend to give you the best parameters to match the method you currently have or better.
Figure: Restek EZGC Method Translator with example parameters.
I’ve used programs like this as a starting point to know what needs changed when moving to a new carrier gas type.
Another challenge to consider is that the carrier is often used as the makeup gas for the detector. You will need to consider this if you have something like an FID. Most cases, users just use the carrier gas for makeup. If you switch your system to hydrogen as your alternative carrier, adding that hydrogen to the makeup (in the same amount as helium) can throw off the required fuel ratio for the detector. Check with the manufacturer for acceptable detector makeup gas options.
The final question that comes up ALL THE TIME in my groups’ technical support queue: “I want to switch to hydrogen, but my lab has safety concerns. What do I need to switch over?” The biggest concern we hear is customers concerned with explosions in the lab. It takes over 4% of hydrogen to fill a space for it to be explosive. In the standard laboratory with normal ventilation and staff moving through the lab, the likelihood of it happening is low when following manufacturers guidelines. In many cases, it will be recommended to use gas cylinders as a lower incoming primary pressure and checking for leaks regularly is important. Where this can be especially important is in the GC oven. It is important to maintain a leak-free environment in the GC for optimal performance but integral when using hydrogen as carrier. Many manufacturers have optional hydrogen sensors that can be installed into the GC with audible alarms to let users know if there are leaks in the system. Another option would be to consider using a hydrogen generator instead of using a tank of gas. Generators also come built with safety features like automatic shutdowns and only generate more pressure as the system is being used.
In general, switching to an alternative gas is easy but some considerations need to be made to determine what is best for each individual lab. It is also important to consider the options for if changing gases just won’t work. While many operators are feeling the challenges of converting, know that you are not alone in this journey!
References
- Restek EZGC Flow Calculator Tool: https://www.restek.com/en/technical-literature-library/brands/EZGC-online-tools/
About the Author: Nicole Lock is the GC Product Manager at Shimadzu Scientific Instruments and a member of the Labcompare Editorial Advisory Board. Nicole graduated from Seton Hill University with a Bachelor of Science in Chemistry. She started her career as a service engineer in a small third-party service organization repairing multiple brands’ GC and GCMS units. This skill set led Nicole to Shimadzu where she has spent the last 15 years working in both the service and marketing department representing the GC and GCMS product lines. Her passion is helping new customers find answers to their unknown problems and current customers make the most of the systems they use every day.