CE-XRF-initial steps toward a non-invasive elemental sensitive detector for liquid separations

Area of Science:

• Analytical Chemistry
• Environmental Science
• Spectroscopy

Background:

• Elemental speciation is crucial for understanding element behavior in the biosphere.
• Capillary electrophoresis (CE) is a powerful separation technique for elemental speciation.
• Existing CE detectors (UV-vis, C4D, PIXE, ICP-MS) have limitations in sensitivity, cost, or practicality.

Purpose of the Study:

• To develop and evaluate X-ray fluorescence spectrometry (XRF) as an elemental specific detector for CE.
• To assess the performance of a custom-built micro-XRF system for elemental detection.
• To explore the feasibility of a low-cost XRF unit for elemental speciation applications.

Main Methods:

• A custom-built micro-XRF detector was developed and tested.
• Static limits of detection (LODs) were determined for 19 elements using modified and unmodified capillaries.
• The micro-XRF detector was coupled with a custom-built CE system for elemental separation experiments.

Main Results:

• Static LODs for 19 elements ranged from 20-926 ppm (unmodified) and 20-291 ppm (modified capillaries).
• Successful separation of Ca2+ and Co2+ was achieved using CE-XRF.
• Elemental sensitivity of XRF enabled signal separation of coeluting Sr2+ and Ca2+.
• A low-cost XRF unit demonstrated feasibility with even lower LODs for Ga and Rb.
• Capillary corrosion, linked to radiolysis, currently limits buffer selection for XRF detection.

Conclusions:

• Custom-built micro-XRF is a viable elemental specific detector for CE, offering high sensitivity and cost-effectiveness.
• The developed CE-XRF system successfully separated and distinguished elements, even when coeluting.
• Further research is needed to address buffer compatibility issues for broader application of XRF with CE.