Rapid Elemental Analysis Spectroscopy Methods

Figure 4. Elemental fortificant distribution analysis of cereal with laboratory micro-XRF.

Image Credit: Bruker

HHXRFs configured with internal libraries of standard alloy and metal grades and compositions identify the contaminants. However, to determine the source of foreign bodies, an XRF audit of all equipment on the production floor is performed first. Simple 30 second test results of all metal surfaces that come in contact with food, or have a potential for breaking, provide a production floor matching catalog. This contains the metal or alloy grade and elemental composition of each piece of equipment, component, piping, or part tested. When more than one source of an identified contaminant is possible from the matching catalog, spectral fingerprint matching is used to take a closer look. Advanced qualitative PC software for HHXRF is used to match the spectral fingerprint of the contaminant to that of its source.

How EDXRF Measures Elements Quickly

Atomic spectroscopy is the most commonly recommended technique for evaluating the elemental composition of samples. It analyzes the interaction between light (energy) and matter (samples). EDXRF is a non-destructive, versatile, and fast spectroscopy technique with minimal sample preparation requirements; and, it can be designed as a laboratory or portable analyzer.

In a way, EDXRF is like a high-powered flashlight that sees beyond what humans can. When the light source is turned on to illuminate a sample, it “sees” the energy of any elements present. It also “senses” how much of those elements are present by their energy’s magnitude. For example, when EDXRF illuminates a sterling silver coin, it detects silver at 22.163 keV and copper at 8.046 keV; and, it determines the coin’s composition to be 92.5 percent silver and 7.5 percent copper.

Figure 5. Ultra-trace analysis capability of arsenic in rice with mobile TXRF.

Image Credit: Bruker

The process of EDXRF elemental analysis of a sample is as follows:

• Energy from an EDXRF source aimed at a sample can eject the sample’s atoms’ inner orbital electrons;
• Outer electrons move into those voids to regain stability;
• While moving in, the outer electrons generate energy characteristic of elements in the sample;
• Resultant energy is detected and processed to determine which elements are present in the sample;
• EDXRF spectrometry results are represented as graphs or spectra showing intensity as a function of energy; and
• The intensity (number of photons) measured at a given element’s energy determines its relative abundance or concentration.

Benchtop EDXRF. These analyzers have the widest range of elemental detection, from light elements such as carbon to heavy elements such as americium with short analysis times, high precision, and excellent detection limits. They are the most versatile in

Figure 6. Internal camera view of metal fragment contaminant in analysis window of handheld XRF.

Image Credit: Bruker

terms of setting up user specific calibrations for virtually any analysis scenario. And, they typically have the most advanced and comprehensive qualitative and quantitative data analysis software capabilities available.

Benchtop EDXRF analyzers are closed-beam systems that can be configured with air, helium, nitrogen, or vacuum atmospheres. Closely coupled thin window X-ray tubes with power up to 50 watts and 50 kV excitation voltage for direct excitation, automatic filter changer selection and high energy resolution silicon drift detectors (SDD) enable the wide elemental analysis and low detection limit range. They are self-contained with a touch screen for user-friendly routine analysis and a variety of connectivity ports. Options typically include internal cameras, automatic sample changers and spinners.

Micro-XRF. This elemental analysis technique with a spatial resolution significantly smaller than conventional EDXRF enables micron size sample analysis. It is especially helpful for analyzing small particle wear debris found during production or particle inclusions in plastic film found during packaging. When micro-XRF is combined with sophisticated elemental mapping software, it is ideal for studying the distribution of nutrients in foods, such as produce, and of fortificants on foods, such as cereal and snacks.