Energy Dispersive X-ray Fluorescence (EDXRF) FAQs

Q1.

What is EDXRF used for?

A1.

EDXRF spectrometry is well recognised as a tool for the qualitative and quantitative determination of major and minor elements in a wide range of sample types. EDXRF's versatility stems from its rapid, non-destructive, multi-element determinations from ppm to high weight percent of elements from oxygen (O) through uranium (U). It can perform these measurements across a wide array of sample matrices: liquids, solids, slurries, powders, pastes, and thin films. EDXRF is also well suited for semi-quantitative determination of elemental content in complete unknowns. Typically free from sample preparation requirements, the XRF technique has broad appeal to research, industrial, and quality assurance analysts. However, it does not provide information on the chemical state of the elements.

Q2.

Can you give examples of applications of XRF?

A2.

Here are just a few examples, many of which relate to Quality Control:

• metals composition
• coatings thickness and composition
• jewelry analysis and certification
• scrap metal sorting/waste re-cycling
• geological and minerals mining samples
• cement, china clay, lime, phosphates etc
• coal and oil
• ceramics and glass
• pulp and paper
• chemicals, catalysts, etc
• plastics, polymers, rubber etc
• engine oil analysis for wear characterisation
• manufacturing process quality control
• agriculture, food, pharmaceuticals etc
• forensics
• art authentication
• archaeology
• environmental e.g. air particulates, contaminated land, fly ash
• materials research

Q3.

A3.

A typical spectrometer uses an X-ray tube to bombard the sample with X-rays of sufficient energy to knock out the inner shell electrons of the sample atoms. Electrons from outer shells then drop down into the vacant inner-shell positions, and characteristic X-rays are given off. This is known as X-ray fluorescence (XRF). In the energy-dispersive technique (EDXRF), the energies of the X-rays emitted by the sample are measured using a Si-semiconductor detector and are processed by a pulse height analyser. Computer analysis of this data yields an energy spectrum which defines the elemental composition of the sample. Essentially, the energy of the peak gives the element identification, and the number of X-rays counted in the peak gives the amount of the element present in the sample.

Q4.

What is the lightest (lowest Z) element that can be routinely quantified with a 'light element option' (EX-3600 or EX-6600) EX-Series Jordan Valley XRF spectrometer? What is the appropriate minimum detection limit?

A4.

Fluorine at 1-2%. Qualitative analysis down to carbon is possible.

Q5.

What is the lowest minimum detection limit (MDL) that can be successfully measured with the EX-Series XRF spectrometers (best case)? What is the most important factor influencing EDXRF detection limits?

A5.

(a)1-2ppm in as-received samples. Significantly better than this with pre-concentration.
(b)Matrix factors i.e.:

• particle size
• other elements
• absolute coefficients and fluorescence yields
• relative concentrations

Q6.

Does XRF require sample preparation?

A6.

In many cases, no preparation is required. This is especially true of homogenous samples like solutions. However, some inhomogenous samples require grinding and pressing prior to analysis for best quantitative results (e.g. for geological samples, etc). If solutions can be pre-concentrated or dried, then proportionately better MDLs can be obtained (see Q5).

Q7.

How long does analysis take?

A7.

Typically from 10 seconds to 30 minutes depending upon sample matrix, elemental concentrations, and desired precision and detection limits. The latter depend on the standard deviation of the X-ray peaks.

Q8.

What is standard deviation? What is the relative deviation? Why is this important in XRF?

A8.

Counting statistics dictate that the goodness, or standard deviation, with which one knows the area of a peak (peak integral) is proportional to the square root of the area (counts): n^½ here n = gross counts for the element of interest (EOI) peak. The relative standard deviation (%RSD) is given by: % RSD = n^½/n × 100. What this says is that the larger the analyte peaks, the better we know the size of that particular peak. Obviously, a larger peak will afford superior reproducibility (better precision) and lower minimum detection limits (MDL) than a smaller peak! As an example, consider two peaks of areas 4 and 16 counts; they can afford a "sigma" of 2 and 4 respectively. The % RSD are then 50% and 25%. Notice that a quadrupling of the peak area (equivalent to increasing the analysis time by a factor of four) halves the % RSD. EDXRF instruments normally provide % RSD's between 10% and 0.5%.

Q9.

What are the principal advantages of JVAR's EDXRF spectrometers over WDXRF instruments?

A9.

• initial cost
• cost of operation
• ease of use
• simultaneous elemental measurement
• flexibility
• suitable for non-technical personnel
• speed of analysis
• no routine maintenance needed
• see all elements, expected and unexpected

Q10.

How do the various EX-Series models differ, and what are their strong points?

A10.

The key points are presented in the main Jordan Valley section of this website.

Q11.

What principal characteristic differentiates the EX-3600 from the EX-6600? What advantage does each type of instrument have over the other?

A11.

The EX-6600 instrument features, in addition to direct excitation like the EX-3600, secondary target excitation. In the secondary target mode, the X-ray tube illuminates a variety of target materials (one at a time); each target then emits its monochromatic characteristic X-ray lines. The resulting monochromatic X-radiation excites the sample material and affords a spectrum with greatly enhanced S/N ratio (up to a factor of 10 better). This improvement is due to the fact that the EX-6600 detector in the secondary target mode does NOT see a sample spectrum superimposed on top of scattered broadband (Bremsstrahlung) radiation (always seen in direct excitation instruments like the EX-3600). The disadvantage of secondary target excitation is that, like source excited benchtop instruments, only a few elements can be efficiently excited at any one time. In contrast, the direct excitation mode of all EX-Series spectrometers can be used to simultaneously excite all elements from Na through U.

Q12.

Are Jordan Valley's instruments difficult to use?

A12.

No. Once set up (and Staplethorne and Jordan Valley personnel can help you with this), they can be routinely operated by non-technical support staff.

Q13.

Are the instruments expensive?

A13.

JV products are breaking new ground in cost-effective high quality XRF instrumentation. Entry level instruments start at around 20% of the price of well known wavelength dispersive systems.

Q14.

Are JVAR EDXRF instruments hazardous?

A14.

The instruments are designed (and surveyed many times to ensure) so that no radiation escapes the unit. The radiation measured at the instrument's surface, at maximum power, is not different than background. Safety interlocks prevent accidental exposure if the sample compartment is opened during analysis.

Q15.

Who are Jordan Valley and Staplethorne?

A15.

Jordan Valley is a long established Israeli company, with a major subsidiary in Texas and expert technical representatives throughout Europe and many other trading areas. Staplethorne, their UK representative, is a company that carries out technical research, product development, and marketing and support of instrumentation for non-contacting/non-intrusive elemental analysis. Staplethorne are also capable of creating specific application procedures and adapting products to meet specific customer needs, and offer UK-based service and support.

Q16.

What support can I get in the UK?

A16.