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

1. Helium Gas Usage

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.

2. Substitution with Other Gases

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.

3. Measurement Methods for Light Elements in Liquids as an Alternative to Helium Gas Purge Measurement

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.

  Liquid Method Drip Filter Paper Method
Pretreatment Place it in a sample container covered with a film Drip it onto the filter paper, and then dry it
Atmospheric Gas Helium None (vacuum)
Materials Used for Pretreatment
· Sample container
· Polypropylene film (5 mm thick)
· Filter paper marked with a ring
Advantages and Disadvantages (Advantage) The liquid can be measured as is, so it is simple.
(Disadvantage) The helium purge option is required for light elements.
(Disadvantage) X-rays from light elements will be absorbed by the film.
(Disadvantage) About 4 mL of the liquid sample is required.
(Advantage) Measurements can be performed under vacuum conditions.
(Advantage) Only a small amount (100 mL) of liquid sample needs to be dripped onto the filter paper.
(Disadvantage) Production repeatability will be low for samples such as organic solvents and oils that will diffuse beyond the confines of the ring on the filter paper.

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