Exposure to chlorate and perchlorate in milk and dairy products can cause harm to human health, with infants and young children particularly at risk. At high concentrations, chlorate and perchlorate are associated with thyroid inhibition and reduced blood oxygenation. Therefore, to ensure consumer safety, robust methods for determining levels of chlorate and perchlorate in milk and dairy products are essential.
Determination of chlorate and perchlorate in milk and dairy products
Ion chromatography (IC) with suppressed conductivity detection is widely used for the determination of chlorate and perchlorate in foods. However, the analysis of milk-based products can be challenging, as matrix components such as proteins, fats, and sugars can interfere with the detection of analytes of interest, leading to inaccurate results. To improve method reliability, time-consuming sample preparation steps such as solid-phase extraction are typically required.
IC coupled with mass spectrometry (IC-MS) has recently emerged as a more sensitive and selective approach for this application. IC-MS enables chlorinated analytes to be more confidently identified using isotope ratios as well as retention times and molecular ion mass, providing greater measurement accuracy while supporting simple and fast sample preparation methods.
The development of advanced column chemistries has further enhanced the reliability of IC-MS techniques. High-capacity, hydroxide-selective anion exchange columns, such as the Thermo Scientific™ Dionex™ IonPac™ AS20 column, provide superior separation of perchlorate from cations and anions across a wide range of sample matrices, achieving more accurate results even at trace analyte concentrations.
A more sensitive and selective approach for chlorate and perchlorate analysis
Chlorate and perchlorate ions were confirmed by matching retention times, m/z, and isotope ion ratios with corresponding authentic standards. Figure 1 shows conductivity and selected ion monitoring (SIM) chromatograms of a vitamin D milk sample spiked with chlorate (m/z 83 and 85), perchlorate (m/z 99 and 101), and their internal standards (m/z 89 and 107, respectively), and highlights the superior selectivity and sensitivity of MS compared with suppressed conductivity detection. The method demonstrated good sensitivity for the detection, identification, and quantification of chlorate and perchlorate ions at concentrations as low as 0.1 μg/L. Calibration curves yielded a linear relationship (r2>0.999) of peak area to concentration for both ions across the range 0.1 to 10 μg/L.
Figure 1. Conductivity and SIM chromatograms of a vitamin D milk sample spiked with chlorate, perchlorate, and their internal standards (1 μg/L).
Using IC-MS to determine chlorate and perchlorate in four milk samples
This method was then used to determine chlorate and perchlorate levels in samples of vitamin D milk, organic whole milk, 2% reduced-fat milk, and fat-free milk. Given the complexity of the sample matrices, isotope ion ratios at the retention times of the internal standards were monitored to confirm the peaks in each sample. Chlorate and perchlorate were found in all four samples, with chlorate content ranging from 152 to 404 μg/L and perchlorate content ranging from the limit of quantification to 7.53 μg/L. Isotope ion ratios for chlorate were all within 25% of the natural ion abundance.
Method precision was evaluated using duplicate injections of the vitamin D milk sample spiked with 1 μg/L chlorate and perchlorate over four consecutive days. The relative standard deviations of the content and retention time for chlorate were 1.22% and 0.60%, respectively, and for perchlorate were 3.34% and 0.17%, respectively, highlighting the excellent precision of this approach. Method accuracy was also validated by determining recoveries of chlorate and perchlorate spiked in vitamin D milk for five replicates at three concentrations (1, 2, and 4 μg/L). Recoveries ranged from 89% to 109%, demonstrating the suitability of this method for chlorate and perchlorate determination.
Finally, the robustness of the system was tested by assessing changes in retention times from more than 900 injections. From the first to the last injection, a retention time change of just 0.24 min was observed for chlorate, while the retention time for perchlorate remained unchanged for the final 200 injections. After 958 injections of standards, deionized water, and matrix extracts, peak shapes remained stable and the column and MS source required no cleaning or maintenance.
Accurate and convenient analysis of challenging food matrices with IC-MS
Advances in IC-MS technologies are delivering impressive improvements in chlorate and perchlorate food testing applications. The IC-MS method highlighted here, using a Dionex IonPac AS20 column and ISQ EC single quadrupole mass spectrometer, achieved sensitive, accurate, and precise chlorate and perchlorate ion measurements in milk with minimal sample preparation.