Inductively Coupled Plasma Mass Spectrometry Method for Analysis of Iodine and Bromine in Feed and Multiple Biological Matrices from Dairy Cattle

The simultaneous determination of bromine and iodine in biological and feed-related samples by inductively coupled plasma mass spectrometry (ICP-MS) is challenged by matrix effects, analyte carryover, and the potential loss of volatile halogen species during sample preparation. This study aimed to develop and validate a sensitive and robust ICP-MS method for determining total bromine and iodine in total mixed ration (TMR), milk, urine, feces, ileum, and duodenum. Samples were prepared using a common alkaline extraction procedure with tetramethylammonium hydroxide (TMAH) followed by centrifugation, filtration, and matrix-specific dilution. Bromine and iodine were measured in SQ-KED and TQ-O2 acquisition modes. Matrix-specific dilution, additional washing between samples, and the introduction of 0.5% ammonium hydroxide (NH4OH) as a rinse solution alongside the existing 0.2% TMAH wash effectively reduced analyte carryover and improved signal stability. Matrix-matched spike-recovery experiments yielded recoveries of 95.7–110.7%, with relative standard deviations of 0.4–5.5% and the majority below 2.5%. Limits of detection (LODs) ranged from 0.01 to 0.25 µg/L, while matrix-dependent lower limits of quantification (LLOQ) ranged from 1.0 to 2.0 µg/L for bromine and from 0.2 to 1.0 µg/L for iodine. Among the evaluated approaches, 81Br TQ-O2 and 127I SQ-KED yielded the overall recoveries closest to 100% across the matrices included in the real-sample analysis and were therefore selected for reporting these results. Bromine and iodine in digested TMR samples remained stable during 30 days of storage at 5 °C. Application to samples from a dairy-cow feeding experiment demonstrated the method’s suitability for detecting treatment-associated differences in bromine and iodine concentrations. The method provides a practical and reliable analytical workflow for determining total bromine and iodine across diverse biological and feed-related matrices.