WDXRF Analysis of Traces in Aqueous Solutions

Analysis of toxic elements and heavy metals as traces in aqueous solutions is becoming increasingly crucial in view of the environmental issues. Such analysis demands high sensitivity and accuracy of measurement.

In XRF, the analysis of liquids can be performed with ease and minimum sample preparation.

Instrument

The Thermo Scientific™ ARL™ PERFORM’X series spectrometer used in this analysis is a 2500 Watt system. This system is configured with four collimators, six primary beam filters, two detectors, up to nine crystals, helium purge and Thermo Fisher Scientific’s 5GN+ Rh X-ray tube for best performance from ultra-light to heaviest elements owing to its 50 micron Be window. This new X-ray tube fitted with a low current filament guarantees an unmatched analytical stability month after month.

Due to a clever management of power, this spectrometer can function up to 2500 W without needing external water cooling. The ARL PERFORM’X offers the ultimate in sample analysis safety and performance. Its exclusive LoadSafe design includes a series of features that prevent any issue during sample pumping and loading. Liquid cassette recognition prevents any liquid sample to be exposed to vacuum by accident. Over exposure safety automatically ejects a liquid sample if X-ray exposure time is too long.

The Secutainer system protects the main chamber by vacuum collecting any loose powders or liquid in a specially designed container, easily removed and cleaned by the operator. For spectral chamber protection, the ARL PERFORM’X employs a helium shutter built for absolute protection of the user’s goniometer during liquid analysis under helium operation. It divides the main chamber from the goniometer chamber. During liquid analysis, helium gas is added only in the main chamber keeping the goniometer under vacuum and a stable temperature.

This allows a fast change-over from vacuum to helium environment, keeps helium consumption to a minimum, and guarantees the best analytical repeatability. In the “LoadSafe Ultra” optional configuration, a special X-ray tube shield offers total protection against sample breakage or liquid cell rupture.

Sample Preparation and Results

Solutions with different concentrations of individual elements are prepared by diluting standard solutions with a blank solution. Therefore solutions with 2, 5, 10 and 100 ppm were prepared from a regular solution of 1000 ppm and measured so as to derive calibration curves. Limits of detection for the many elements were calculated from these curves.

Figure 1 illustrates a scan on a sample containing trace quantities of Hg and As in a water solution. Table 1 lists the lines used, crystal-detector combinations and usual limits of detection obtained for the different elements. X-ray tube conditions were fixed at 60 kV and 41 mA. Cd is measured with a main beam filter to eliminate overlap from rhodium tube lines.

Figure 1. XRF scan showing traces of Hg and As in water.

Table 1. Analysis parameters and typical limits of detection (100 s counting time).

FPC= flow proportional counter
SC = scintillation counter
* = Cd is analyzed with a primary beam filter to suppress overlapping lines due to the rhodium anode of the X-ray tube

For guaranteed values the above limits of detection should be doubled.

Conclusion

The analysis of aqueous solutions can be performed quickly and with ease using the mid power sequential XRF spectrometer ARL PERFORM’X at 2500 W. The limits of detection for toxic elements and heavy metals range from 0.2 ppm up to 1 ppm in 100 seconds counting time. Thus, the ARL PERFORM’X is well-suited for the analysis of typical industrial water or waste water.

Using this mid-power XRF spectrometer also allows the installation to be simpler as it does not require external water for X-ray tube and anode cooling, thereby eliminating the need for neither tap water, nor a water cooler.

Additionally, the operation is made simple through the most advanced sophisticated Thermo Scientific OXSAS WDXRF software which works under the latest Microsoft Windows^® 10 package.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers.

For more information on this source, please visit Thermo Fisher Scientific - Elemental Analyzers.