The Specialty Gases division of Welders Supply has been packaging extra high purity gases, extra high pressure cylinder gases, and liquid and gas mixtures since 1978.
Our customers depend on the accuracy of our work, as well as our ability to respond to their demands for unusual gas mixtures and gas products. Common examples fo gas products that Welders Supply provides are:
We offer certified multi-component mixtures in the low part per million range. Our analytic methods include gas and liquid chromatography, infrared, paramagnetic, chemiluminesence, and gravimetric methods.
We obtain the highest purity liquids available and fill our specially prepared cylinders.
To insure that no impurities are introduced, we fill these cylinders using stainless steel piping and diaphragm packed valves. The cylinder of gas is then tested for trace hydrocarbons, trace oxygen and moisture. Further contamination analysis for the higher purity gases is done in our gas chromatograph.
Certification is available if requested. Also, aluminum cylinders are available.
There are 3 basic standards for mixture tolerances:
We also offer EPA Protocol and NIST traceable mixtures.
Primary Standards – This is generally used when the highest accuracy and reliability is demanded. These are prepared on a very accurate balance. Depending upon the components and quantities accuracy can be to 4 places. These mixtures are recommended for critical calibrations and testing.
A signed certificate of analysis is supplied, which includes statements of traceability to NIST and evaluated accuracy. Multicomponent and non catalog Primary standard gases are available on request.
Certified Standards – By far the most common type of standard. This standard is prepared in the lab and analyzed against lab standards by using various analytic techniques such as Gas Chromatography, Infrared, etc.
Tighter blend tolerances and analytical accuracy, as well as a signed certificate of analysis are available upon request.
Unanalyzed Mixture – A blending of components with no actual statement of analysis. These mixtures are used in applications which do not require analytical verification of component concentrations.
Blend tolerance is the range that the minor components will fall into.
Analytical Accuracy is also known as Certification Tolerance. It describes how accurately the mixture was analyzed, or how accurate the preparation was. Analytical Accuracy varies with the type of components and their volume in the mixture.
NIST: This is the National Institute of Standards and Technology, formerly known as the NBS or National Bureau of Standards. There are a number of gas standards sold by the NIST. These mostly deal with environmental issues such as Vehicle Exhaust Testing. The standards each have a number, Example “1680B”. The lab doing the cerfitification to NiST 1680B would have to possess the standard, use it to calibrate the analytic instrument, and provide documentation on the statement of analysis.
SRM: Standard Reference Material, This term is used to describe a NIST material.
Traceability to NIST class S weights: For a large range of requested gas standards there are no NIST gas standards available. The analysis is referenced to highly accurate & costly Class S weights used in conjunction with a gas cylinder balance. This type of preparation can result in 4 decimal place accuracy.
Reactivity & Stability
These two terms come into focus when dealing with reactive & unstable compounds. Some examples of these are Sulphur Dioxide, Nitric Oxide, Hydrogen Sulphide, Ammonia, Low ppm Carbon Monoxide. This type of compound, especially when in the low concentrations, have a tendency to react with the cylinder walls, valves, or balance gas. The only assurance that we have as a producer is to blend and analyze the mixture, wait a number of days, repeat the analysis and compare results. If the concentration remains the same the mixture is said to be stable.
As a general rule of thumb, the lower the concentration of a reactive compound, the shorter the Stable life.