Potential Natural Scapolite Reference Materials for <i>In Situ</i> Cl and Br Measurement by <scp>LA</scp> ‐ <scp>ICP</scp> ‐ <scp>MS</scp>

The mass fractions of Cl and Br in melt, fluid and mineral phases are crucial for tracing geological processes, exploring ore deposits and assessing environmental impacts of volcanic halogen degassing. However, the scarcity of well‐characterised reference materials for in situ Cl and Br measurement remains a significant challenge. Here, a suite of gem‐quality scapolite samples from world‐wide was characterised by laser ablation ICP‐MS, electron probe microanalysis (EPMA) and instrumental neutron activation analysis (INAA). The results revealed reproducible mass fractions in scapolite samples TSNY (3.63 ± 0.13% m/m Cl; 319 ± 12 μg g ‐1 Br), MDJ (3.01 ± 0.20% m/m Cl; 225 ± 16 μg g ‐1 Br), and BX (2.76 ± 0.07% m/m Cl; 251 ± 15 μg g ‐1 Br), which were identified as optimal calibration materials across a broad range of Br mass fractions. Additionally, samples SM (2.76 ± 0.13% m/m Cl; 1186 ± 146 μg g ‐1 Br), AFH (3.92 ± 0.14% m/m Cl; 44 ± 3 μg g ‐1 Br), and XJ (3.82 ± 0.10% m/m Cl; 42 ± 3 μg g ‐1 Br) served as effective secondary reference materials for quality monitoring purposes. Ablations were conducted with a 90 μm spot size, 5 Hz repetition rate and 100 ms dwell time, with 35 Cl and 81 Br identified as the preferred isotopes for accurate Cl‐Br quantification. The scapolite samples demonstrated excellent calibration performance, with 2 RSD and bias values between 6 to 7% and 0.8 to 1.6%. This work provides a reliable set of reference materials for Cl‐Br measurement, enhancing the precision and accuracy of LA‐ICP‐MS in geological research.