EDS & WDS - The Differences and Uses

EDS -  Energy Dispersive X-ray Spectroscopy 

WDS -  Wavelength Dispersive X-ray Spectroscopy

Energy-dispersive X-ray spectroscopy (EDS) and wavelength-dispersive X-ray spectroscopy (WDS) are two techniques used to determine the elemental composition of materials. Although both methods involve the detection and analysis of X-rays emitted from a sample, they differ fundamentally in their approach. EDS is often referred to as a qualitative analysis technique, and WDS is often referred to as a quantitative analysis technique.

All-In-One (EDS) | One-From-All (WDS)

EDS employs a semiconductor detector to measure the energy of emitted X-rays. This detector captures the entire energy spectrum simultaneously, enabling the identification of multiple elements within a single measurement. In contrast, WDS utilizes a crystal monochromator to separate X-rays based on their wavelengths. By adjusting the crystal's orientation, specific X-ray wavelengths can be isolated and their intensities precisely measured.

It's all in the details:

WDS boasts superior energy resolution compared to EDS, allowing it to resolve closely spaced X-ray lines and differentiate elements with overlapping emissions. This high resolution makes WDS the preferred choice when accuracy and precision are paramount. Conversely, EDS exhibits greater sensitivity to lower-energy X-rays.

Faster Vs. More Accurate:

EDS offers faster data acquisition due to its ability to measure the entire X-ray spectrum concurrently. This rapid analysis makes EDS suitable for applications requiring quick elemental information across a wide energy range. WDS operates more slowly, as it necessitates scanning through different crystal positions to select specific X-ray lines.

*LMAC Lab Note: For this reason our lab uses EDS to get a "realtime" assessment of a sample's overall modality (mineral composition) before doing more time consuming WDS analysis. We also use EDS to map BSE image shades to their respective mineral phases. This allows us to choose appropriate analysis points by their shade rather than doing EDS before selecting every single point. EDS can also be extremely useful for identifying obviously terrestrial minerals without the need for WDS. One example of this is when we use EDS to distinguish between non-meteoritic metals or oxides, and the meteoritic iron-nickel alloys kamacite and taenite.

Uses and Integrations:

EDS is frequently coupled with both electron probe microanalyzers (EPMA) and scanning electron microscopes (SEM) for elemental analysis. WDS cannot be integrated with scanning electron microscopes (SEM). EDS and WDS are almost always integrated with electron probe microanalyzers (EPMA) for both fast and precise elemental analysis, especially in geological and metallurgical samples where realtime qualitative analysis, and quantitative high accuracy and resolution are critical.

In conclusion, EDS and WDS both provide valuable elemental analysis capabilities, but their distinct detection methods, resolutions, speeds, and applications cater to different analytical needs. While the choice between EDS and WDS depends on the specific requirements of the analysis and the characteristics of the sample under investigation, they are often used in concert with EDS being used as the preliminary analysis technology and with WDS used to drill down more accurately into what was initially identified using EDS.