Elemental and statistical analysis of small individual urinary stones using TXRF spectrometry

Due to the small quantity of most of the extracted human urinary stone samples, there is an urgent need for an analytical technique that is able to perform a multi-elemental quantitative analysis for a small fraction of these samples. In the present work, a few milligrams of different types of urinary stones were microwave digested in ultra-pure nitric acid, and the elemental determination was achieved by total reflection X-ray fluorescence (TXRF). The elements P, S, Ca, Fe, Cu, Zn, Se, and Sr were detected in most of the different stones. However, the trace elements: K, Ti, V, Cr, Mn, Ni, As, Pb, and U were also found in a certain number of samples. Furthermore, inductively coupled plasma optical emission spectrometry (ICP-OES) was used and the elements Mg, Ti, Mn, Cu, Zn, and Cd were determined. A good agreement between the results of TXRF and ICP-OES was obtained with respect to the elements Ti, Mn, Cu, and Zn. Cadmium and magnesium were only determined by ICP-OES. More attention was given to the existence and the spectral interference of As-K-alpha and Pb-L-alpha as well as As-K-beta and Br-K-alpha in a limited number of urinary stones. Based on the analysis of variance and Pearson's correlation analysis, an additional statistical analysis study was performed in terms of quantified elements and the types of urinary stones. Calcium has a remarkable positive correction with Ni, Zn, and P, whereas a negative correlation was found with K, S, and Cu. Based on the hierarchical cluster analysis, the square Euclidean showed four main groups of urinary stones starting with high to trace amounts of calcium oxalate. Furthermore, the squared Euclidean showed further subgroups of the urinary stones. The role of certain elements in terms of forming or inhabiting the urinary stone formation was discussed. Uranium was determined in a limited number of urinary stones using TXRF and ICP-OES. The origin of the uranium may be the drinking and groundwater. Uranium could be accumulated in the urinary stones from these sources. In addition, the divalent uranium compounds can deposit on the surface of hydroxyapatite crystal, which is one of the main compounds in the urinary stones.

Automated summary

A multi-elemental quantitative analysis technique was urgently needed for small quantities of human urinary stone samples. Microwave digestion with ultra-pure nitric acid and total reflection X-ray fluorescence (TXRF) were used for elemental determination in this study. P, S, Ca, Fe, Cu, Zn, Se, and Sr were detected in most urinary stones, while trace elements K, Ti, V, Cr, Mn, Ni, As, Pb, and U were found in some samples. Inductively coupled plasma optical emission spectrometry (ICP-OES) was also used for element determination. Statistical analysis and cluster analysis were conducted to explore the relationship between quantified elements and stone types. The role of certain elements in urinary stone formation was discussed, and the presence of uranium in some stones was confirmed.