Knowing the Answer Can Make a Big Difference in Analytical Test Results
Laboratory gases will always play a significant role in the everyday life of anyone working in any lab. A gas chromatograph (GC) or a mass spectrometer (MS) is just a sizable paperweight without gases. But with the myriad gases and gas grades to choose from and gas company representatives who are not always up to speed on the upper end of the specialty gas spectrum, how does one make the best choice?
Industrial gases versus specialty gases
Standard gases that are used in tasks such as welding or metal cutting are called “industrial gases.” Tanks are filled with the gas of choice for the application and shipped out to the customer. When the tank comes back empty it is simply refilled, and out the door it goes again.
This is not the case with specialty gases. A specialty gas must meet or exceed a particular set of specifications and should never be allowed to leave the gas company’s gas lab until the cylinder in question has proven its worth under great scrutiny. Using ultra-high-purity (UHP) helium as an example, let’s walk through the process involved in earning the coveted “ultra high purity” status. First, the cylinder is fitted with a positive open/ closed valve that ensures a high level of leak integrity. Second, the cylinder must be treated to a baking process to remove any contaminants from the inside of the cylinder walls. The tank is placed in an oven and baked for eight hours at 140ºF. During the baking process, the tank is purged with an inert ultra high purity gas and then quickly placed under vacuum. This purge/ vacuum sequence is repeated seven times during the eight-hour baking period.
The purpose of this process is to break the polar bond of any existing moisture molecules that have affixed themselves to the inside of the cylinder walls. This thermal energy transfer frees the molecules from the cylinder walls and the purge/vacuum process removes the contaminants from the tank. Trapped within these moisture molecules are other harmful contaminants such as hydrocarbons and particulates. When this process is complete, the cylinder is clean enough on the inside to accept and maintain the integrity of an UHP gas. We can introduce our prepared cylinder (now under vacuum) to its new occupant, the UHP helium. Once the cylinder is filled it goes to the lab, where chemists put the cylinder through a battery of tests to check for contaminants such as moisture, total hydrocarbons and oxygen. Once the cylinder has passed that test, it moves on to the gas chromatograph to again prove its worth. Passing the analysis by the GC earns the tank a shrink-wrapped valve and a place within the “specialty gas” family. If these procedures are not followed, it is akin to putting clean milk in a dirty thermos—you are going to get dirty milk out. Dirty gas delivered to equipment that is expected to utilize UHP gases will cause adverse results.
Trying to save a few dollars on gas purchases might seem like a frugal thing to do, but it can come back to bite the unsuspecting buyer. If a gas company is not quite up to speed with specialty gases and their applications as well as the adverse results to the customer’s equipment, it may very well deliver an industrial gas to a life science or R&D lab. The results can be very damaging for the end users. Industrial-grade helium used in a GC will jam the columns with moisture in the hundreds or thousands of parts per million (PPM) level and render the test results useless. Another contaminant that will wreak havoc is hydrocarbons, which will surely be in excess and cause additional problems. This scenario always results in a repeat of the failed analysis, repeat processes, replacement of the gas tank and repair work to the GC along with a considerable dose of aggravation. Any gas that needs to meet a particular specification is a specialty gas and is truly special. Trying to replace a specialty gas with an industrial gas in order to save a few dollars at the onset will surely cost the buyer considerably more money downstream.
Ultra-high-purity helium must meet the following specifications:
|Moisture (H2O)|| |
|Total hydrocarbons (THC)|
By contrast, industrial-grade helium may have many hundreds or even thousands of PPM of each contaminant.
Gas-related equipment is critical
Even with the right UHP helium in your lab, you are not yet ready to deliver it to your process. The gas pressure regulator that goes on the tank is as important as the gas grade itself. If an industrial-grade regulator is put on an ultra high purity gas cylinder, the gas will be contaminated right back down to an industrial grade quality. Industrial-grade regulators commonly have neoprene diaphragms, and neoprene is a hydrocarbon (contaminant). They also have a very low leak integrity and can draw moisture (contaminant) into the gas stream along with a dose of oxygen (contaminant) from the air.
A good choice for UHP helium is a pressure regulator that has a leak integrity of 1 x 10-9. It will also have stainless steel diaphragms and Teflon and Tefzel seats and seals. This regulator will maintain the integrity of the UHP helium and deliver it to your process as intended, with no issues.
Don’t forget the process line either. We would hate to go through all the trouble above just to have someone put a rubber-based hose on the regulator to deliver the gas to process. UHP helium requirea stainless steel hose with a stainless steel core. A standard stainless steel pigtail is commonly Teflon lined, and very fine helium molecules will find their way right through the Teflon and out into the atmosphere. Go the last step to ensure the integrity of the gas by purchasing the right hose.
Now you have the right grade of gas, the right regulator and the right hose to deliver the gas to process. What is left to do? Enjoy your analytical test results without fear of contamination from the gases or gas-related equipment.
Partner your business with a gas company that has the answers to your questions and has the right people in the field with a broad knowledge base regarding the products they sell and the equipment you use. Be sure there is an elevated level of service that goes along with your gas purchases.