Comparison and optimization of analytical techniques for accurate phosphorus determination in high-titanium geological samples

Abstract

The precise assessment of phosphorus in geological samples with high titanium levels poses analytical difficulties because of interferences from titanium-rich compositions in the matrix. To precisely quantify phosphorus, this study assesses and optimises several analytical techniques, such as X-ray fluorescence (XRF) and inductively coupled plasma optical emission spectrometry (ICP-OES) after sample preparation by acid digestion (AD), peroxide fusion (PF), pressed pellet (PP), fused bead (FB) and microwave-assisted extraction (MAE). The samples were certified reference materials (CRMs) containing titanium. When combined with a proper sample preparation method such as MAE, ICP-OES showed greater accuracy, whereas XRF scan offered quick, non-destructive analysis but had sensitivity limits. From the 6 methods that were tested, the best recoveries (83.1–100 %) of certified values were consistently obtained by MAE/ICP-OES followed by AD/ICP-OES analysis among the studied procedures and FB/XRF (98.3–105 %), demonstrating its efficacy in breaking down resistant mineral phases and overcoming matrix interferences. The relative standard deviation (RSD) ranged between 0.25 % and 2.1 % for MAE/ICP-OES and 0.30–5.3 % for FB/XRF, indicating good precision. Based on the ANOVA results, the phosphorus concentrations obtained from the different analytical methods showed statistically significant differences across all the CRMs analysed (P < 0.05). However, MAE/ICP-OES and FB/XRF proved to not be contributing to the significant difference when assessed using an Honesty Significant Difference (HSD) test. These findings demonstrate that MAE/ICP-OES and FB/XRF methods provide more accurate, precise and repeatable phosphorus quantification in samples rich in titanium. In addition to phosphorus, the samples were also analyzed for associated metal oxides and rare earth elements, which commonly co-occur in high-titanium geological matrices. These determinations were essential to assess matrix interferences and improve the reliability and accuracy of phosphorus quantification methods.