Elemental assessment of dried and ground samples of leeches via portable X-ray fluorescence†
Determination of elemental concentrations in animal tissues is critically important due to the extensive use of animal tissues in food and medicine. Traditionally, elemental analysis has mostly relied on laboratory-based methods, such as inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Portable X-ray fluorescence (XRF) spectrometry, which has been widely applied in soil and rock analysis, has rarely been used to quantify elements in animal tissues. In this pilot study, the effectiveness of using pXRF to determine elemental concentrations in leeches was demonstrated. The effects of the moisture content and compaction (density) on pXRF readings were experimentally quantified. The penetration depth of X-rays in leech samples is generally <15 mm. For leech samples with different thicknesses (thicknesses ranging from 2.5 mm to 15 mm), measured pXRF elemental concentrations were found to decrease with increasing sample thickness in a power function, the square of the correlation coefficient (R2) of which was 0.96 and 0.89 for Zn and Fe, respectively. Therefore, the thickness correction for intermediate sample thickness is possible in future analysis, enabling a more accurate analysis for samples with insufficient sample mass. The detection limits determined for As and Cu in dried and ground leech samples with a thickness of ∼15 mm were ∼5 and ∼20 mg kg−1, respectively, which were equal to/lower than the regulatory limits for both food and medicine. The pXRF measured concentrations of S, K, Fe, Cu, Zn, and As were highly correlated with ICP results (R2 ≥ 0.92), with the exception of Ca (R2 = 0.81). Simple linear regression models were employed to predict the ICP-based elemental composition of 15 leech samples using pXRF elemental data as inputs; the validation results were quite good for all the studied elements (R2 ≥ 0.92). Thus, pXRF shows great potential for safety control of elemental concentrations in food and medicine.