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Different applications call for different high-quality gas mixtures. The main mixture types are described below.
Specific instrument calibration gases
An instrument is called “specific” if it measures one specific substance (or family of substances) only and cannot be used for others. Specific instruments are typically calibrated with a zero gas and one or more span gases. Zero gas is normally a pure gas not containing the component to be measured, and is as similar to the matrix of the measured sample as possible. Normally this is synthetic air or nitrogen. The purity of the zero gas must be sufficiently high for the application in question (grade 5.0 to 7.0). For a typical single-point calibration, the span gas will ideally have ppm concentrations corresponding to 90% of the ppm value to be measured (if measuring 50 ppm, for instance, the span calibration point will be 0.9 x 50 = 45 ppm.).
At Linde, our standard mixtures therefore have concentrations corresponding to 90% of typical ppm values to be measured, always ensuring that we can offer you the products that perfectly match your individual needs.
General instrument calibration mixtures
An instrument is described as “general” if the instrument can be used to analyse a wide variety of chemical substances. General instruments like gas chromatographs (GC) are often calibrated by creating a calibration line or curve covering the intended measuring range.
Our standard products are used to generate the calibration points for these lines or curves. Highly optimised production processes and analysis methods allow us to offer calibration mixtures that accurately match your requirements for precision while satisfying all applicable standards (e.g. for manufacturing tolerance, measurement uncertainty and traceability). The accuracy of our instrument calibration mixtures gives you the reassurance that your analytical results are always accurate.
Threshold monitor mixtures
Special monitors are used to identify occupational or fire hazards and warn employees accordingly. These are specific instruments that raise an alarm when a pre-set concentration of the substance monitored is reached. High-quality gas mixtures for these types of applications typically have half- and full-time weighted threshold limit value concentrations for the substance in air (if this is not possible, nitrogen is used). The typical concentrations for flammable products are 20, 40, 50, and 60% of the Lower Explosion Limit (LEL). Bump test gases are a typical example of gases required for this threshold monitoring.
Here also, our threshold monitor mixtures work within narrow blending tolerance and analytical uncertainty ranges to give you the accuracy you need. In addition, by offering a selection of typical concentrations at 20, 40, 50 and 60% LEL, these mixtures can make a valuable contribution to safety in the workplace.
Most liquefied hydrocarbon mixtures are supplied in a cylinder where head space has been pressurised using a high-purity inert gas such as helium. This prevents the lighter hydrocarbon components from separating after final production. To maintain composition during use, the mixture may be supplied in a cylinder using a dual port valve to allow additional pressure to be fed into the cylinder to maintain the head space pressure.
We also offer customised mixtures provided they are compatible with the chemical and physical properties of the gases requested and that they do not compromise our strict product stewardship policy. Safety is always our number one priority.
For more information please consult our product catalogue.