Improvement in the Reliability of AOAC Official MethodSM 2012.15 for Iodine, Part-2.

Background: In our previous study, the AOAC Official MethodSM2012.15 (Method 2012.15) was modified by adding carbon (as methanol) to the standard and final test solutions for accurate quantification of iodine in infant and special formulas after incomplete matrix oven digestion. However, when an inductively coupled plasma-mass spectrometry (ICP-MS) instrument from a different manufacturer was used, inaccurately low iodine content values were obtained using both the original and modified methods.

Objective: To obtain more reliable values for infant formulas using varying ICP-MS instruments.

Methods: The protocol was modified by changing the ratio of the pump tubing inner diameters (IDs) for the ICP-MS system or by optimizing the internal standards for Method 2012.15.

Results: No significant improvement was observed by changing the ratio of the pump tubing IDs. In the optimization study of the internal standard, when germanium is used as the internal standard, the measurement result of NIST SRM® 1849 was within the certified value range. Furthermore, with the addition of methanol equivalent to 5% to the standard and final test solution based on our previous study, the recovery of the samples was within the certified range of SMPR 2012.008.

Conclusions: This demonstrates that changing the internal standard to germanium and adding methanol equivalent to 5％ to the standard and final test solution, can result in stable measurement even when the ICP-MS specifications were changed.

Highlights: The modified Method 2012.15 provides reliable results even if the instrument is changed by changing the internal standard to germanium.