Tackling low Z element quantification with TXRF

Abstract

Total Reflection X-ray Fluorescence (TXRF) is a powerful analytical technique used to detect and quantify low Z elements in various scientific and industrial applications. The detection limits of TXRF are impressive, with the ability to detect elements in the parts per billion (ppb) range, making it an ideal technique for trace element analysis. However, as the atomic number of elements decreases, it becomes increasingly demanding to quantify their chemical composition. To address this issue, we have calibrated our low Z spectrometer at the Atominstitut to quantify samples consisting of Na, Mg, Al, K and Ti with Ca as internal standard with very good agreement to a NIST 1643f reference. The experimental setup of our instrument consists of a 900 W X-ray tube with a chromium anode and a line focus. We have used a multilayer monochromatorto produce a narrow energy bandpass of about 300 eV. In addition, we use a silicon drift detector with an ultra-thin 70 nm detector window (SiN) to minimize absorption and enable efficient detection. We measure under rough vacuum conditions of about 1 mbar to reduce air scattering and absorption effects We also calibrated our instrument at th ree angles of incidence, twice below and once above the critical angle of our PMMA reflectors. Our results showed that the result is invariant to the angle of incidence below the critical angle, further demonstrating the reliability and reproducibility of our measu rements. We also quantified carbon samples by measuring a mean value for the blank reflector and subtracting this value to obtain the concentration. As all surfaces are covered with a natural carbon layer, subtracting the blank value improved the accuracy and precision of our measurements. Our results showed good agreement between the measured and true concentrations, indicating the effectiveness of our calibration method. Furthermore, we measured an elemental depth profile using X-ray photoelectron spectroscopy (XPS) to investigate the elemental composition of the sample surface. Our results showed that up to 60 at% of the surface is carbon, which is consistent with our previous observation that a natural carbon layer covers all surfaces. In conclusion, our study demonstrates the utility of TXRF for the accurate and precise quantification of low Z elements. Our calibration method allows reliable measurements of trace elements with detection limits in the parts per billion range. The use of TXRF in conjunction with careful calibration and validation can provide valuable insight into the chemical composition of materials, environmental samples and biological systems.