X-Ray Fluorescence (XRF) spectrometry is a non-destructive analytical tecnique based on the characteristic emission of X-Ray photons by atoms when returning to the ground state after an excitation. This property is used to obtain elemental information from different types of materials in several fieds.
The basic Energy-Dispersive XRF (ED-XRF) set-up consists of an X-Ray tube as the excitation source, a sample housing and a semi-conductor detector which allows to discriminate between different energy photons. The angles between the incident X-Ray beam, the sample and detector are equal to 45 degrees in order to minimize the scattered background.
TXRF is founded on the same principles of the EDXRF with, however, one significant difference. In contrast to EDXRF, where the primary beam strikes the sample at an angle of 45 degrees, TXRF uses a glancing angle of a few milliradians with the detector positioned very close to the sample at 90 degrees.
Owing to this grazing incidence, the primary beam is totally reflected by a flat substrate (carrier) onto which the sample is deposited in liquid/slurry form and then dried in order to leave only a thin residue film, ideally some nanometer thick. The total reflection condition provides an enhanced fluorescence excitation, while the reduced thickness allows to get rid of any matrix effect: thus, the signal to background ratio is enhanced and for each element a simple linear relationship between its characteristic fluorescence peak intensity and concentration exists.
Quantitative analysis can be performed by adding an internal standard to the sample solution/suspension, i.e. an element which is not present in the original sample (usually Ga, Sc, Co or Y). Then a small droplet, about 5-100 μL, is taken from the solution/suspension with the internal standard and deposited onto the carrier.
The technique is generally non-destructive and it is suitable for solids, liquids, powders and alloys. Depending on the sample, analysis can be carried out on the "as is" specimen or after a treatment step, e.g. dilution, digestion, ashing, on-site enrichment etc. In many cases, the correct sample preparation is instrumental in getting low LOD and accurate qualification.
- No matrix effects
- A single internal standard greatly simplifies quantitative analyses
- Calibration and quantification independent from any sample matrix
- Simultaneous multi-element ultra-trace analysis
- Several different sample types and applications
- Minimal quantity of sample required for the measurement (e.g. 5-10 μL)
- Unique microanalytical capabilities for liquid and solid samples
- Excellent detection limits up to pg/g (ppt) or pg for all elements from sodium to plutonium
- Excellent dynamic range from ppt to percent
- Possibility to analyse the sample directly without chemical pretreatment
- No memory effects
- Non destructive analysis
- Low running cost