Specialty Gas Mixtures are used in various applications. Such type of mixtures are defined generally by their function rather than their chemical properties. SIGAS manufactures majority of the more common Two component, Three component and multi-component mixtures. These mixtures can be categorized as below:

1. Calibration Gas Mixture
2. Special Application Mixture

Types of Mixture Standard:
SIGAS has simplified the ordering method by standardizing mixture gases into three categories.

1. Primary Standard
2. Secondary/Certified Standard
3. Unanalyzed Standard

Primary Standard:
SIGAS has prepared this standard by weighing the gas component on a high sensitivity balance using NIST certified weights. This method results in the closest tolerance available. Additional verification of mixture accuracy is then performed by quality control analysis. Primary Standard is used when your application demands the highest mixture accuracy and reliability.

Certified Standard:

SIGAS prepare this standard by using partial pressure and gravimetric techniques. Certified Standards are analyzed mixtures used widely in various laboratories, Instrumentation calibration, environmental control measurements, biological and medical applications, and chemical process.

Unanalyzed Mixtures:

Theses mixtures are produced using the same technique as the Certified Standard, but they are not checked by analysis. Unanalyzed mixture should only be used where accuracies are not critical.

• Mixtures containing low molecular weights depending on their concentration.
• Multi-component mixture depending upon the type, number, and concentration of components.
• Mixture containing components which presents adsorption, stability, or other blending problems.

While referring the above table, you must understand the Blending Tolerance and Certification Accuracy. Blending tolerance is the maximum deviation from the required concentration of the minor component where as Certification Accuracy is the maximum deviation from the certified value of the minor component.

Blending Restrictions:
Every mixture has a characteristic dew point curve, which is a series of pressure / temperature relationships at which the gas will begin to condense to a liquid. This may result in a change in the composition of the gas phase. To eliminate the possibility of condensation, the cylinder pressure is reduced, keeping it below the dew point pressure.

Restrictions due to Reactivity and Stability:
Some gases when mixed become instable, reactive, or may be adsorbed onto the walls of the cylinders due to their chemical and physical properties. Sometimes these reactions take place only under pressure or may be due to the material of cylinders. SIGAS technical team will advise you of the problem and will suggest you the right kind of cylinders.

Restriction due to Flammability:
SIGAS can prepare the mixtures containing an oxidant and a flammable, but only under very stringent conditions. SIGAS will not prepare the mixture in which the flammable and oxidant concentrations exceed both of the lower explosive limit of the flammable and the minimum oxidant required for combustion. SIGAS will also not produce the mixtures in which these two parameters are exceeded at high pressure during filling. There are many criteria used to determine the safety of a blend containing an oxidant and a flammable. SIGAS technical team will evaluate your specific requirement and will offer you a alternative product, suitable and safe for use.

Method of Trace-ability:
Mixtures supplied by the Specialty Gas Division of SIGAS are traceable to NIST standards by the following methods:

• Mixtures may be certified directly against NIST standard reference gas
• Mixtures are compared to the secondary standard that have been analyzed by comparison to NIST standard reference gas.

In the case of non-availability of NIST standard reference gas, the mixtures are analyzed by comparison with gravimetrically prepared Primary Standard produced by SIGAS and made on precision balance using weights traceable to NIST.