Development of a comprehensive method for hair and nail analysis using laser ablation-inductively coupled plasma-mass spectrometry

Hair and nails have been increasingly used in human biomonitoring (HBM). The advantages of these samples are non-invasive sampling, stability, and ease of storage. Elemental analysis using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a promising approach to retrieve information about long-term exposure to toxic elements; however, the lack of standardized analytical protocols hinders its application. In this work, Mn, Cu, Zn, Sr, Y, Pb and U were selected as model elements for developing analytical methods. Several critical aspects of the method were evaluated. We found that line scan resulted in higher reproducibility in nail analysis as compared to spot scan. Nail samples with a thickness of 0.5 mm were found to be best for LA-ICP-MS analysis. Regarding the sample cleaning, contaminants on hair were effectively removed by successive washing of acetone and ultrapure water; results were validated by the cross-section images of hair. Pre-ablation with a laser energies of 0.06 mJ per pulse and 1.03 mJ per pulse using higher scan rate and spot size were shown to be an effective method to remove the contaminants on undyed nails and dyed nails, respectively. Dried droplet calibration using element-enriched filter paper as calibration standards was developed for the quantification of elements. A new preparation of pressed pellet of hair CRM powder with sodium tetraborate was employed to validate the method. The recoveries of the model elements ranged from 97.2 to 105.4 %. Our study demonstrates that LA-ICP-MS can be used for high throughput elemental analysis of hair and nail samples, and has potential application in future HBM studies.