Ever wonder why two labs can test the same sample and get different results, or why one XRF analyzer can cost $20K while another tops $200K? The truth is, you are not alone; not all XRF is created equal.
The two most common techniques are Energy Dispersive XRF (EDXRF) and Wavelength Dispersive XRF (WDXRF). EDXRF and WDXRF use different approaches to elemental analysis, which can impact many factors, like accuracy and speed.
Each of these techniques offers its own advantages, limitations, and ideal applications. Choosing the right one is more than a technicality. It can mean the difference between rapid screening and lab-grade precision, which can directly affect your productivity and profitability.
In my years-long XRF journey, I have worked extensively with both of these techniques. In this article, I am going to walk you through their fundamental differences, what each of these techniques is, how they work, and where they are used the most.
Fundamental differences between EDXRF and WDXRF
Bringing the comparison full circle: EDXRF or WDXRF?
| Factor | EDXRF | WDXRF |
| How it detects elements | Measures X-ray energy using semiconductor devices | Measures X-ray wavelengths using diffraction crystals |
| Resolution (distinguishing close elements) | Sharp peak, very little peak overlap | Very sharp peaks with almost no peak overlap |
| Instrument power | Lower power (4–100 W), meaning a smaller footprint, lower costs, and often portable or transportable options | Higher power (200 W–4 kW), meaning bigger and more expensive instruments, but also higher sensitivity |
| Element range | Sodium to Uranium (11Na to 92U) | Beryllium to Uranium (4Be to 92U) |
| Cost | $15,000 - $100,00 | $80,000–$500,000+ |
EDXRF and WDXRF differ in how they resolve and detect characteristic X-rays. EDXRF uses semiconductor detectors to directly resolve the energy of the X-rays emitted from the sample to identify and quantify the elemental composition of a material. Alternatively, WDXRF uses analyzing crystals and diffraction to indirectly resolve the X-ray wavelengths to perform elemental analysis.
A good thing to understand is that there is a relationship between the energy and wavelength of X-rays. The formula E (keV) =12.4/λ (Å) shows how the energy of a photon is related to its wavelength, where E is the photon energy in kiloelectronvolts (keV) and λ is the wavelength in angstroms (Å). Since energy and wavelength are inversely proportional, shorter wavelengths mean higher energy, while longer wavelengths indicate lower energy.
EDXRF uses semiconductor detectors (commonly Silicon Drift Detectors, or SDD) to measure the energy of all fluoresced X-rays at once, providing a high total count rate and enabling fast, simultaneous analysis of multiple elements. However, resolving signals that are very close in energy can require additional consideration.
In contrast, WDXRF separates X-rays by wavelength using analyzing crystals, and counts them individually with detectors (gas-filled proportional counter or scintillation counter) capable of handling high count rates. This enables highly precise analysis and accurate identification of overlapping signals. The tradeoff is that, in sequential instruments, measurement time increases in proportion to the number of elements analyzed.
Another key distinction is power. Power refers to the system’s ability to generate X-rays. Higher power means more X-rays are produced, which results in a stronger signal from the elements in the sample.
EDXRF typically operates at lower tube power because, when semiconductor detectors are used, the optics can be positioned close to the sample. This makes it well-suited for portable and benchtop instruments.
In contrast, WDXRF requires higher-powered X-ray tubes because its longer optical path and use of analyzing crystals reduce efficiency. Therefore, stronger excitation is needed to reliably measure elements at low concentrations, which also means the instruments tend to be larger.
Because EDXRF systems generally operate at lower power, their analytical range typically spans from sodium (11Na) to uranium (92U). Some high power WDXRF systems can extend this range down to beryllium (4Be).
Thanks to their streamlined design, EDXRF spectrometers are generally lower in cost, with handheld and benchtop models ranging from $15,000 - $100,000. This makes them ideal for industrial quality and process control. WDXRF spectrometers are typically more expensive, with models ranging in price from $80,000 - $500,000 or more. WDXRF spectrometers are more expensive due to their higher-power X-ray tubes, complexity, and having more moving parts, yet they can deliver more precise results for the more challenging applications.
To learn more specifics about cost, read the article: How Much Does an XRF Spectrometer Cost?
In XRF, a sample is exposed to primary X-rays, which excites the atoms in the sample. This excitation happens when the incoming X-rays have enough energy to knock electrons out of the inner shells in the atom, creating vacancies. Electrons from higher energy shells then drop down to fill these gaps, releasing energy as characteristic secondary (fluorescent) X-rays. These are then analyzed and used to calculate elemental concentrations.
Want to learn more about how XRF works? Visit an article: What is X-ray Fluorescence (XRF)?
EDXRF systems use primary beam filters to shape the background X-rays or use secondary targets to remove the background X-ray signal. The EDXRF detector then simultaneously detects the X-rays emitted from the sample.
In EDXRF, the detector captures both the energy and intensity of the fluorescent X-rays. As a result, multiple elements can be quantified concurrently. There are two excitation approaches used in EDXRF: direct and indirect.
Direct excitation
The primary X-ray beam from the tube passes through a filter to minimize background noise and is then used to excite the sample directly.
Indirect excitation
The primary X-rays from the tube strike a secondary target, which then emits X-rays to excite the sample. This geometry greatly reduces background noise and improves the peak-to-background ratio for enhanced sensitivity.
Figure 1: Direct vs indirect EDXRF
WDXRF uses primary beam filters to shape the background X-ray noise. The fluorescent X-rays emitted from the sample first go through a collimator (or a slit), which makes the X-rays more parallel. One or more crystals are then used to diffract the X-rays at a specific wavelength to detect the secondary X-rays from specific elements. A detector is placed at a particular angle to read the X-ray intensity from the targeted elements.
There are two types of WDXRF: sequential and simultaneous.
Sequential WDXRF
Measures elements one at a time by mechanically moving the crystal and detector to collect intensity for each wavelength, providing high precision for a wide range of elements.
Figure 2: Sequential WDXRF
Simultaneous WDXRF
Employs multiple fixed channels to simultaneously measure several elements, increasing throughput, making it ideal for high-volume quality control environments.
Figure 3: Simultaneous WDXRF
EDXRF: The tube produces the primary X-rays by accelerating electrons toward a metal anode (commonly made using palladium, silver, or rhodium), where the impact generates the X-rays used to excite the sample.
WDXRF: Just like EDXRF, the tube produces the primary X-rays used to excite the sample. X-rays are generated by accelerating electrons toward a metal anode (such as palladium or rhodium).
EDXRF: These filters are placed between the X-ray tube and the sample. They work by filtering out certain energies, which helps reduce background noise, effectively creating “quiet spots” in the spectrum.
WDXRF: As with EDXRF, these filters are positioned between the X-ray tube and the sample. They selectively absorb parts of the tube spectrum, reducing unwanted background and enhancing the clarity of element peaks for more precise measurements.
In indirect EDXRF, secondary targets are placed between the X-ray tube and the sample. Unlike the beam filters, which simply reduce background radiation, a secondary target creates a monochromatic excitation beam that is directed at the sample. This beam not only improves detection limits but also helps eliminate background noise.
In WDXRF, these crystals are used to diffract (separate) the fluorescent X-rays emitted by the sample based on their wavelengths. As a result, it enables elements to be differentiated and allows for these elements to be measured precisely. There are various types of crystals used in WDXRF, each used to optimize the sensitivity and resolution for specific elements.
EDXRF: The detector is used to measure the energies of the X-rays emitted from the sample. This enables it to identify the elements in the sample and determine their concentrations. The most common detectors used in EDXRF are silicon drift detectors (SDD) and positive-intrinsic-negative (PIN) diode detectors.
SDDs provide greater resolution and sensitivity, making them ideal for applications requiring precise elemental analysis. In contrast, PIN diodes have moderate resolution, which is effective for elemental measurements where high resolution is not essential.
WDXRF: After the X-rays are diffracted by the analyzing crystals, the intensity of the X-rays is measured by a detector. This enables the identification and quantification of the elements in the sample. For WDXRF, flow-proportional counters (F-PC) and scintillation counters are commonly used detectors, each suited to analyze different element ranges based on their detection characteristics.
F-PCs are generally used for elements such as magnesium, aluminum, and silicon, as they provide better sensitivity for these lighter elements. Conversely, scintillation counters are a more robust option that are used to analyze heavier elements, such as iron, nickel, and copper.
To learn more about EDXRF, visit: What is EDXRF?
To learn more about WDXRF, visit: What is WDXRF?
EDXRF is favored when speed, simplicity, and versatility are essential. Its ability to measure multiple elements simultaneously with minimal sample preparation and lower costs makes it ideal for situations where throughput and convenience matter more than high levels of sensitivity. Some common EDXRF applications include:
WDXRF is preferred for applications where maximum resolution, precision, and accuracy are necessary. By measuring elements sequentially (or simultaneously with advanced systems), WDXRF provides enhanced spectral separation and lower detection limits, which makes it the best option for complex or trace-level analysis. Some common WDXRF applications include:
In many industries, these techniques aren’t exclusive but complementary. EDXRF offers rapid, on-site analysis with reliable quantitative results, while WDXRF provides laboratory-grade precision and high-resolution data.
To learn more about what XRF can analyze, visit this article: What XRF Can and Can’t Analyze: A Guide for Beginners
Choosing between EDXRF and WDXRF ultimately comes down to the analytical needs for your specific application. EDXRF is a versatile technique that excels at rapid, multi-element analysis, making it ideal for high-throughput environments or routine quality control. WDXRF is valued for its superior spectral resolution and higher accuracy, making it the go-to choice for trace elemental analysis and more complex applications.
Both techniques are an integral part of elemental analysis, each playing an important role with its own unique advantages. The best choice, whether EDXRF, WDXRF, or a combination of both, will depend on your application. Hopefully, after reading this article, you have a better understanding of the differences between EDXRF and WDXRF. If you still have questions, you can reach out to one of our experts to learn more about each technique and find the right XRF solution for you.