Energy dispersive x-ray fluorescence analyzers (ED-XRF) are increasingly being used for low level detection of elements in complex matrices due to advances in XRF instrumentation and the desire to perform non-destructive analyses. The X-Calibur, manufactured by Xenemetrix, is one example of an instrument that provides the user with the flexibility to easily change multiple parameters (measurement conditions) to achieve optimal accuracy when quantifying different elements of interest.
The ability for the instrument operator to set various conditions (some are detailed below) is of greatest interest to laboratories that have a wide range of material analysis occuring during a day, such as organizational quality control labs, general testing labs, and academic laboratories. By pre-setting these operating conditions, the user will be able to quickly switch from one condition to another depending on the measurement goal. This wil save set-up time, increase analyzer accuracy and most likely extend the life of major components.
The first step in method development to ensure good signal is to utilize the minimal voltage required to excite the element of interest. Increasing the voltage beyond the ionization energy of the target element will increase the baseline noise by producing interfering x-rays from heavier elements. For example, if measurement of Nickel (Ni) was desired, with an excitation energy of 7.477kV, by only applying 9kV of voltage, the elements beyond Ni in the periodic table are not excited. This results in less interfering x-rays and an increased signal of the peak of interest. Understandably, when the measurement of a heavier metal is desired, such as Gold (Au), an increase in baseline is expected due to the higher voltage required. However, an increase in the signal can be achieved by increasing the amperage.
Filters can also be used to increase the signal of contamination level elements. Filters essentiallly absorb x-rays in the field of interest that would interfere with the detection of these elements. For example, light elements such as Phosphorus (P) do not require the use of a filter because of the lower voltages used. As previously noted, this would produce an increased baseline. However, it would be advantageous to use a Titanium (Ti) filter if measuring low levels of Mangenese (Mn), to diminish interference from other transition metals that may fluoresce from the matrix.
Secondary targets are also worth mentioning as they can increase the flexibility of the instrument to allow for the detection of a larger array of elements. For example, Molybdenum (Mo) is a common source in x-ray tubes; however, if the measurement of low level Sulfur (S) in petroleum is desired, the analyst would find that a Molybdenum (Mo) source emits x-rays that interfere with the measurement of Sulfur (S). By using a secondary target such as Silver (Ag), the interfering x-rays are removed, thereby allowing the sample to be hit with the secondary x-rays that maintain the characteristics of the target and do not interfere with the measurement of low level Sulfur (S).
This is just another benefit that ED-XRF technology offers an end-user. Contact an Application Specialist to discuss how multiple conditions may benefit your laboratory or review more information on Xenemetrix analyzers that offer the option - The X-Calibur allows the functionality to easily change filters or voltages to obtain an optimal signal in a complex matrix. Other models, such as the EX-6600 Laboratory Spectrometer, would allow for the use of secondary targets as well.