Helium Usage by the EDX Helium Purge Unit, and Alternative Analytical Methods

Three L/min of helium gas are used by the EDX series helium purge unit. Analysis starts after a 3- minute flow, and the same flow rate is used during analysis.5- minute analysis, usage is as follows. (3+5) min × 3 L/min = 24 L As a result, 24 L of helium gas are consumed per analysis. Note that the flow rate cannot be changed, as this would have an impact on the analysis results.

In measurements under atmospheric conditions, fluorescent X-rays generated by the sample are absorbed by the nitrogen and oxygen in the air. This results in reduced,sensitivity, particularly at the low energy end (light elements). For this reason, light element analysis is generally performed under vacuum conditions. However, liquid samples cannot be measured in a vacuum:as an alternative, the vacuum is replaced with helium gas, which absorbs fewer fluorescent X-rays than nitrogen or oxygen. The smaller the atomic number, the smaller the absorption, so replacement with gases with a molecular weight comparable to or larger than air (with an average molecular weight of 28) is ineffective. In addition, hydrogen gas, which has a low molecular weight, cannot be used for safety reasons. Therefore,the only alternative is helium gas.

In terms of X-ray fluorescence spectrometry, the drip filter paper method is often used to analyze liquid samples.With this method, droplets of the liquid are dripped onto the filter paper, and analyzed after drying. A dried sample is used, and nabling analysis to be performed under vacuum conditions.