Gas purity validation is performed using a TOC (Total Organic Carbon) measurement, carried out using a gas chromatograph with an FID detector. This measurement shows the total carbon content, divided into volatile (TOC v) and non-volatile (TOC nv). This can then be checked against the specification.
The measurement is performed by pumping controlled air through the channels of the product to be tested using a ‘tenax’ tube. Any carbon compounds present are absorbed and chemically bound to the tenax material. The tube is then heated in a gas chromatograph, causing the carbon compounds to ‘evaporate’ and become measurable.
In the GC detector, the carbon compounds are converted into electrons. By measuring these electrons, it becomes clear how much and which carbon compounds were present. If the requirements are slightly exceeded, the channels can be flushed with XCDA, followed by a new TOC measurement. If the requirements are significantly exceeded, the product will need to be cleaned again.