Determination of iodine in polyamide by inductively-coupled plasma/mass spectrometry

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

Background

In our previous study, the AOAC Official MethodSM  2012.15 (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.

Challenges and trends for halogen determination by inductively coupled plasma mass spectrometry: A review

RATIONALE

In this review, works published in the past 25 years for fluorine, chlorine, bromine, and iodine determination in several matrices by inductively coupled plasma mass spectrometry (ICP-MS) were covered. Usually, the determination of halogens has been performed by ICP-MS using a previous sample preparation step or, more recently, by direct analysis of solid or liquid samples.

METHODS

Methods based on combustion, extraction, pyrohydrolysis, sample dilution in organic or aqueous medium, and wet digestion, among others, are discussed. Moreover, the recent applications of methods based on laser ablation (LA) and electrothermal vaporization (ETV) coupled to ICP-MS are discussed.

RESULTS

The main challenge for methods using sample preparation has been to obtain a final solution compatible with ICP-MS, as well as to overcome problems related to analyte losses and contamination. Interferences due to the presence of dissolved organic compounds in solution, enhancement or suppression of ionization of analytes, and related matrix effects have been of concern when using ICP-MS. For the determination of halogens by ICP-MS using LA and ETV systems, some limitations related to the difficulty of calibration are pointed out, impairing the widespread use of this approach.

CONCLUSIONS

A critical view is presented for further halogen determination by ICP-MS, mainly for matrices considered difficult to digest using conventional protocols.