Two Candidate Natural K‐Feldspar Reference Materials for In Situ Pb Isotope Measurement

Accurate and precise in situ Pb isotope measurement in K‐feldspar by laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS) requires matrix‐matched, isotopically homogeneous K‐feldspar reference materials (RMs) to correct for instrument‐induced mass bias. Although the Shap and Albany K‐feldspars are widely utilised, expanding the suite of available RMs is imperative to enhance quality assurance and control (QA/QC) and improve inter‐laboratory data comparability. This study presents the systematic characterisation of two natural K‐feldspars, KFS‐04 and KFS‐05, as new candidate RMs. Major and trace element measurements classify both samples as orthoclase. The Pb mass fractions range from ~ 90 to ~ 165 μg g ‐1 , while the Pb isotopic composition is homogeneous at the micrometre scale. In situ LA‐MC‐ICP‐MS analyses of the KFS‐04 and KFS‐05 K‐feldspars yielded mean 208 Pb/ 204 Pb ratios of 38.705 ± 0.029 (2 s, n = 299) and 38.689 ± 0.028 (2 s, n = 303), 207 Pb/ 204 Pb ratios of 15.693 ± 0.012 (2 s, n = 299) and 15.697 ± 0.011 (2 s, n = 303), and 206 Pb/ 204 Pb ratios of 18.270 ± 0.023 (2 s, n = 299) and 18.326 ± 0.022 (2 s, n = 303), respectively. These in situ data are consistent with the solution‐based analysis data determined by SN‐MC‐ICP‐MS, which yielded mean 208 Pb/ 204 Pb, 207 Pb/ 204 Pb and 206 Pb/ 204 Pb ratios of 38.7118 ± 0.0087 (2 s, n = 5), 15.6916 ± 0.0029 (2 s, n = 5), and 18.2705 ± 0.0036 (2 s, n = 5) for KFS‐04, and 38.6964 ± 0.0225 (2 s, n = 4), 15.6923 ± 0.0084 (2 s, n = 4), and 18.3260 ± 0.0101 (2 s, n = 4) for KFS‐05. The demonstrated isotopic homogeneity and matrix‐matching characteristics suggest that KFS‐04 and KFS‐05 are robust candidate RMs for in situ Pb isotope measurement.