Determination of Ultratrace Level Perchlorate in Liquid and Powdered Baby Formula

Perchlorate is a widespread contaminant in the United States.1 Research has demonstrated its presence in various media, including water, soil, various foods, and also human biological fluids, such as urine and breast milk.2-6 Perchlorate causes an adverse health effect by competitively inhibiting iodide uptake by the thyroid gland because it exhibits a much higher selectivity factor than iodide.7 The reduced uptake of iodide inhibits thyroid hormone production, which is essential for proper protein expression, neuronal differentiation, and other functions.6 Certain populations, for example, infants and children, may be at higher risk due to their greater dependency on milk products and higher consumption/ body weight ratio. Health Implications of Perchlorate Ingestion, a report issued by NAS, has strongly encouraged continued research on the potential exposure routes and adverse effects of perchlorate contamination in sensitive populations.8 Analytical methods for perchlorate quantification include ion chromatography (IC), equipped with various anion-exchange columns, and conductivity and/or mass spectrometric (MS) detections.5,6,9,10 The high sensitivity and selectivity of MS detection makes it a highly preferred method for complex sample matrices. Thus, MS detection provides greater data confidence while minimizing labor-intensive sample preparation. This study describes an IC-MS/MS method for ultratrace-level perchlorate analysis in both liquid and powdered baby formula. Without sample enrichment, perchlorate in baby formula matrix can be quantified at low parts-per-trillion (ppt) levels with simple sample preparation. Linear calibration was established in the range from 20 ppt to 10 parts-perbillion (ppb), with a coefficient of determination (r2) greater than 0.999. Recovery was achieved at 103% and 114% by spiking 5 ppb perchlorate in two samples. Repeated injections of standards showed %RSDs from 1.82% (100 ppt) to 7.36% (10 ppb); repeated injections of one prepared baby formula sample showed %RSD of 3.63%; and repeated assays (n=3) of samples showed %RSD from 1.63% to 3.55%. Perchlorate was found in every tested sample of commercially available infant formula obtained from local markets, ranging from 1.02 to 2.43 ppb. EXPERIMENTAL SECTION Ion Chromatography Conditions System: ICS-3000 RFICTM system Column: IonPac® AS16 and AG16 hydroxide-selective anion exchange columns (2 mm) ASRS® 300 self-regenerated suppressor (external water mode) Column Temp.: 30 oC Flow Rate: 300 μL/min Mobile Phase: Isocratic 45 mM hydroxide generated from EGC-II KOH cartridge Solvent: 150 μL/min acetonitrile delivered by AXP-MS pump Detection: 1st detector: Suppressed Conductivity 2nd detector: TSQ Quantum AccessTM Mass Spectrometer Mass Spectrometric Conditions: System: TSQ Quantum Access Triple Quadrupole Mass Spectrometer Interface: Electrospray Ionization (ESI) Source Spray Voltage: 4000 V Sheath Gas: 40 arbitrary units Auxiliary Gas: 5 arbitrary units Ion Sweep Gas: 15 arbitrary units Capillary Temp: 300 oC Collision Gas: Argon at 1.8 mTorr Operating Mode: Selected Reaction Monitoring (SRM) Analyte Parent Ion Product Ion Collision Energy Perchlorate 99.1 83.2 24 Perchlorate 101.1 85.1 24 Perchlorate-O4 107.1 89.2 24 Leo (Jinyuan) Wang, Stacy M. Henday, Charles Yang, William C. Schnute Dionex Corporation, Sunnyvale, CA, USA; Thermo Fisher Scientific, San Jose, CA USA Determination of Ultratrace Level Perchlorate in Liquid and Powdered Baby Formula