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

Abstract

The toxicity, bioavailability, and mobilization of elements within the biosphere is dependent on its species. CE has emerged as a strong separation technique for elemental speciation. Conventionally, CE has been coupled with UV-vis, C⁴ D, PIXE (proton-induced X-ray emission), and ICP-MS. UV-vis and C⁴ D are not elemental sensitive detection methods, PIXE requires the etching of the detection window resulting in a very brittle capillary, and ICP-MS is an expensive large footprint instrument. Here, we aim to develop an elemental specific detector, XRF (X-ray fluorescence spectrometry), for use with CE. A custom-built micro-XRF was tested and static LODs were determined for 19 elements (Ca-U) with both unmodified (20-926 ppm) and modified capillaries (20-291 ppm). A custom-built CE was combined with the micro-XRF and separation of Ca²⁺ and Co²⁺ was obtained. Sr²⁺ coeluted with Ca²⁺ in the mixture, but because of the elemental sensitivity of XRF, the Sr and Ca signals could be separated. After successful testing of the micro-XRF, the feasibility of using a low-cost X-ray source and detector was tested. Even lower LODs were obtained for Ga and Rb, showing the feasibility of a smaller, low-cost XRF unit as an elemental specific detector. However, the buffer selection that can be conveniently used with XRF is currently limited due to capillary corrosion, likely correlated to radiolysis.

Keywords: CE; Elemental speciation; XRF.