In recent months, the growing shortage of helium has gained national attention and raised concerns of availability and cost among users. Laboratories in particular rely on helium for analytical applications, as well as tasks other than its primary use as a carrier gas, i.e., blowing off samples, operating valves, purging gas, and more.
The helium shortage is expected to improve this year, but the current tight supply is causing many laboratories to consider converting their gas chromatography systems to utilize hydrogen instead of helium to counteract rising costs and localized supply issues. Hydrogen does have benefits when optimally set up and maintained; however, the conversion process is quite complex and extremely time consuming.
Considerations prior to hydrogen conversion
Many steps need to be considered and addressed before converting to hydrogen. Labs must be properly vented, and a review of the electrical classifications of rooms must be conducted to ensure that National Fire Protection Association (NFPA) regulations and local fire codes are met, since hydrogen will be vented in directly. Manifolds and regulators need to be checked for leaks because hydrogen molecules will pass through a leaking connection at a faster rate than helium molecules. If stainless steel tubing is used as the gas line, it must be 316 stainless steel GC grade. If less than 316, hydrogen will cause the tubing to become embrittled, increasing the possibility that the line will break and vent hydrogen into the lab. If tubing cannot be confirmed as 316 stainless steel, it should be replaced.
The GC’s internal gas lines need to be checked for leaks and some lines may need to be rerouted. The entire inlet and detector systems should be cleaned to remove contaminants. The column should be replaced, or one meter of the front removed and the column reconditioned. In some low-flow situations, labs may need smaller i.d. columns to enable the correct backpressure for the system. Next, labs must consider the new linear gas ranges, flow rates, split ratio volumes, make-up gas rates, and hydrogen flow to the detector that must be optimized or changed. Peak identifications also need to be revalidated and quantified. Also, the effort to switch to hydrogen may not provide complete separations and may result in peak coelutions. This multistep conversion process from helium to hydrogen is not always successful and interrupts the work flow of the laboratory, resulting in lost time and additional cost.
Staying the course with helium
Conversion to hydrogen is commonly being promoted and may appear to be a quick fix to shortage and cost concerns. However, labs should take a look at the potential savings in helium usage that is being wasted through delivery equipment leaks, incongruous systems, standard operating procedures (SOPs), and nonprocess applications. Addressing these conservation opportunities can result in significant savings.
By shifting focus from conversion to conservation of helium with the three steps outlined below, labs will typically experience a 20–50% savings in their current helium usage, more consistent results, and extended column and component life, making conservation an alternative—and, most times—better solution than conversion.
1. Determine actual usage
A lab should determine its actual usage to quantify how much helium is being wasted from leaks, permeation, and tasks apart from its carrier gas capabilities. Actual gas process flows should be measured and compared to the monthly amount of helium delivered by cylinders and tanks to pinpoint just how much helium is being misused. Labs should measure gas flows for each GC inlet system using helium. This will provide flows for the column, make-up gas, split vent, and septum vent.
Most GC applications use less than 13 standard cubic feet of helium if running 24 hours a day, 7 days a week for 30 days. Therefore, one cylinder of gas can typically support six GCs using helium for four or more months (capillary GC with dual 0.25-mm-i.d. columns). This typical gas usage value does not include the use of a gas saver mode. Moreover, if the GC’s gas saver mode is engaged, this usage is reduced even further.
Figure 1 shows typical GC gas usage. To determine the gas flows of 13 cu ft/month for a GC, the following calculations and values were used. The formula Fc = 60 πr2ū was used to determine the column flow, where:
Figure 1 – Typical GC gas usage.
Fc is the column flow; π = 3.1415; r2 = radius of the column or, in our case [(0.25/2)/10]2 = .0001562; and ū = average linear gas rate for helium of 20 cm/sec.
This yields a column flow of 0.59 cc/min. To determine the split ratio flow at the split vent, a typical split ratio of 100/1 for a 0.25-mm-i.d. capillary column was used. To obtain this split ratio, the splitter flow would need to be at 59 cc/min., or 59/.59 = 100/1. The septum vent flow is still at 3 cc/min and the make-up gas is at 39 cc/min:
- Column flow: 0.59
- Splitter flow: 59.00
- Septum flow: 3.00
- Make-up gas flow: 39.00
Total: 101.59 cc/min
Converting cc/min to cu ft/month, a factor of 0.0649 is used, or 101.59 × 0.0649 = 6.59 cu ft/month, or with two inlets per GC = 13.1 cu ft/month per GC.
A lab will often discover that usage numbers are significantly smaller than what is being delivered and consumed each month. Helium is wasted due to leaks, permeation, being multipurposed, and other sources of loss throughout the lab. Once the quantities of actual usage become clear, waste or misapplication may be corrected to help conserve supply.
2. Evaluate changeout processes
If a lab’s gas supplier recertifies cylinders ultrasonically, instead of using older hydrostatic methods, there is no need to change out cylinders in the lab at 500 psi, as is done per SOPs written long ago. This modification in changeout process can significantly reduce monthly helium usage. Since most GC applications require only 50–70 psi, cylinders can be changed out at 100 psi. A cylinder changed at 500 psi has 54 cubic feet of gas remaining, yet a cylinder returned at 100 psi has only 12 cubic feet of gas left in the cylinder. This results in a 20% savings and is a major aid in conserving helium. Additionally, now that cylinders are recertified per the Department of Transportation (DOT) standards prior to filling using an ultrasonic test method, lower pressures may be used without risk of contamination.
3. Assess gas delivery equipment
Figure 2 – Check valve CGA cutaway on a regulator.
Finally, laboratories should conduct an evaluation of all gas delivery equipment to assess areas of leakage and potential helium savings. Each gas cylinder connection, referred to as a CGA, should have a check valve built into the nose of the nipple to prevent large volumes of ambient air from entering the system during cylinder changeout. This will eliminate the need to purge air out of the lines that entered during the changeout process, preventing high volumes of air from flowing through purifiers and shortened column life. Air removal requires waste and time investment, so this simple integrated check valve in the CGA will make a significant impact on operations, as well as conservation efforts (see Figure 2).
It is also recommended that labs identify and discontinue use of any flexible hose with a PTFE inner core. PTFE is permeable by both helium and hydrogen, and causes a 5–8% loss of each cylinder’s volume. It also allows for permeation of oxygen and moisture into the system, contaminating the gas, possibly damaging the columns, and causing baseline disturbances. Instead, flexible hoses should contain 316 stainless steel cores. These are leaktight in all gas services, including helium, and are specially cleaned for analytical applications.
Additional gas handling equipment that should not be used in a helium line application includes packed valves, lubricated ball valves, rubber diaphragm regulators, and tubing properly cleaned for GC applications.
By evaluating actual usage, current processes, and gas delivery equipment, a laboratory can typically conserve 20–50% of its helium usage—a savings significant enough to negate the need for an expensive and time-consuming conversion to hydrogen. By working toward conservation, laboratories can maximize their helium supplies during a shortage, and can ensure they remain more efficient and cost-effective long after a shortage is resolved.
Frank Kandl is Product Manager, Specialty Gas Equipment, Airgas, Inc., 259 N. Radnor Chester Rd., Radnor, PA 19087, U.S.A.; tel.: 610-687-5253; e-mail: email@example.com. Reginald Bartram is a Gas Chromatography Consultant and past president of the Chromatography Forum of Delaware Valley.