It is often not easy to distinguish between industrial gases and laboratory gases or special gases. Most of the compressed gases have industrial applications, in fact compressed gases are considered as industrial gases. For this reason, in order to distinguish between industrial gases and laboratory gases, in addition to application, other factors such as complexity, degree of purity, and assurance of composition should also be considered.
Compressed gases are often grouped into 5 unrelated families: atmospheric, fuel, refrigerant, toxic, and those with no clear relationship to other families. The division of these families is somewhat arbitrary and usually based on the origin of the gas, the type of use, or the chemical structure of the gas. Laboratory gases can belong to any of these families, basically they are industrial gases that have been upgraded to a higher level. The dictionary defines the word special as: extraordinary, special, high efficiency or quality standard, so special gas can be defined as a gas with excellent characteristics for special applications. These gases are prepared by laboratory methods to measure, eliminate or minimize the undesirable characteristics in the gas. For special gas mixtures, a precise combination of the concentration of the mixture components is necessary.
Special pure gases
Pure gas is a special gas that is used as a gas for laboratory instruments. Such as chromatographs, mass spectrometers and other types of analyzers and detectors. Manufacturers of these ultra-sensitive instruments usually specify the degree of purity of the pure gases used in their instruments. For example, high-purity helium without moisture is used as a carrier gas in these instruments. When an unwanted impurity is present, the performance of these laboratory instruments is impaired or the instrument itself may be damaged. As a rule of thumb, when the degree of purity (sometimes as high as 99.9999%) is high, or when the amount of impurity is low, a pure gas can be considered as a special gas.
Special pure gas is well used in the production of semiconductors and other similar controlled applications. They are also used to check and control the quality of pure bulk gas. Carbon dioxide is a good example, CO2 (drinkable) gas used in the production of carbonated drinks can be considered as a bulk gas. Because it is used in large quantities. On the other hand, the degree of purity is very important in health; Therefore, to calibrate the instrument used to control the purity of bulk CO2. A special pure CO2 in which all the small impurities are carefully measured is required.
Laboratory gas mixtures (special)
Most of the special (laboratory) gases also exist as a mixture. When it comes to the components of the mentioned special mixture, we face some limitations; Especially gas mixtures that are often used with a variety of analyzers for process control and regulatory compliance. Some specific gas mixtures are somewhat standardized and may include 3 or 4 components such as nitric oxide or sulfur dioxide mixtures, which are used by utilities (water, electricity, oil, etc.) to calibrate the system. Continuous monitoring and emission (CEMs) are used. Other mixtures may be quite complex, for example, containing 30 or more constituents. In order to verify the accurate measurements of the constituents of the mixture, a standard reference material (SRM) is usually used. It provides traceability to common measurement standards from recognized metrology institutes (such as the National Institute of Standards and Technology (NIST)). Certain mixtures usually have components measured on the parts per million and parts per billion scale (PPM & PPB).
Laboratory analyzes for quantification of components and impurities in a particular gas mixture are always important and sensitive. For each cylinder that contains a specific mixture, an official document known as a certificate of authenticity or product quality management is prepared. For some specific pure gases, this certificate includes the following: concentration values for all contents, composition method, type of laboratory analysis, reference standard used to prepare the gas mixture, and expiration date.
Expiration date is the period of time that the components of a mixture remain within a certain limit of the determined concentration. Depending on the stability of the ingredients, shelf life can range from 6 months to 2 years or more. In order to increase the useful life of the gas mixture, special cylinder preparation processes such as noble gas preparation can be used to condition the inner walls of the cylinder.
Specialty gases are not usually used in bulk quantities like industrial gases and are supplied in high-pressure aluminum or steel cylinders that contain more than 3,000 pounds per square inch (psig) of pressure. For this reason, they are sometimes called cylinder gases or capsule gases. The cylinder itself usually does not include the price of the particular gas inside it and must be returned to the gas supplier when the gas is empty. A small monthly rental (for the cylinder) is usually paid until the cylinder is returned. Many special gases are also available in small, portable cylinders that do not need to be returned. Other special containers include bottles that are often used in laboratories and floating piston type cylinders that are used to store volatile liquid mixtures.