Reference Measurements for Priority and Essential Trace Elements and Methyl Mercury with Isotope Dilution Inductively Coupled Plasma-Mass Spectrometry for Seafood Safety Assessment and CRM Production

Abstract

The continuous release of anthropogenic pollutants into marine environment increase the needs for the development of analytical procedures for their accurate determination in many sample types. Sound strategies for seafood safety monitoring call for measurement systems capable of producing comparable analytical results with demonstrated quality. Method validation, traceability and uncertainty of analytical results are the three milestones to assess data quality. Some trace elements are essential for biological structures, but they can become toxic at concentrations beyond those necessary for their functions; others, are toxic even at very low levels. Their accurate determination in reference samples serves as an important step in seafood safety control and pollution monitoring.Isotope Dilution Inductively Coupled Plasma Mass Spectrometry (ID ICP-MS) has been applied for the determination of the total mass fractions of five trace elements (Cd, Cu, Hg, methyl mercury (MeHg), Pb, and Zn) in marine biota candidate reference material IAEA-476. Because of the complex matrix of the sample and the expected spectral interferences, special care was taken for the validation of the applied methodology, particularly for its measurement step. Reference isotopic measurements were carried out by Sector Field Inductively Coupled Plasma Mass Spectrometer (ICP-SFMS).The entire ID ICP-SFMS measurement procedure was described by mathematical modelling and the combined uncertainty of measurement results estimated. All factors influencing the final results and isotopic equilibrium were systematically investigated. This included the procedural blank, the moisture content in biota samples and all factors affecting the blend ratio measurements (i.e., instrumental background, spectral interferences, dead time, mass discrimination effects as well as the repeatability of measured isotope ratios).Modeling of the entire measurement procedure and the use of appropriate certified reference materials (CRM) enable to assure the traceability of obtained values to the International System of Units (SI).Finally, the developed procedure has been successfully applied in the process of the certification of the International Atomic Energy Agency (IAEA) certified reference material for trace elements and MeHg mass fractions in fish homogenate sample. The excellent agreement between obtained results in the present study and those derived from the IAEA certification campaign for trace elements and MeHg in the same sample matrix further validated the reference methods developed in the IAEA.

Assignation of inorganic mercury and methylmercury mass fractions in a soil matrix certified reference material by two analytical methodologies based on species‐specific isotope dilution mass spectrometry and chromatographic separation

“…After that, the extract (in four replicates) was carefully decanted into a 15 ml polypropylene tube and centrifuged for 10 min at 170 × g to completely separate the solid phase. About 8 ml of extract was collected and used for classical chromatography due to the quantitative separation of MeHg from iHg [8,15,30]. For this purpose, 1 ml of 36% HCl was added to extracts, and solutions were poured into four separate ion exchange columns filled with the AG 1X-8 resin.…”

“…In such a case, the chromatography in the classical state can be proposed as a good alternative to the HPLC, because before SS ID ICP MS measurements the separation of MeHg and iHg is mandatory. It should be highlighted that the separation protocol performed with the classical chromatography was applied before only for biota samples (oyster, scallop, and clam) or fish tissue [8,15,30], which are organic and much simpler matrix than soil material. There was a risk that it would not be possible to elute MeHg effectively in the presence of rich soil components and at the ultratrace level.…”

“…After that, the element recovery need not be quantitative, any losses of a sample or further dilution/evaporation will not concern the isotope ratio and the analytical result will not be affected as only a ratio of the number of isotopes, not an absolute amount of the analyte is measured [11][12][13]. Species-specific (SS) ID MS has a great potential in speciation analysis, among other measurement methods, where interconversion and transformation of species cannot be verified [14][15][16][17][18]. Thus, after spiking and controlling the crucial step of isotopic equilibrium achievement, species conversions can be traceable and corrected as well as mass spectrometer drift [11,18,19].…”

Atomic spectrometry update: review of advances in the analysis of clinical and biological materials, foods and beverages

“…Among several areas of concern, the accurate measurement of potentially toxic elements in marine species is necessary for the purpose of both assuring food safety and monitoring pollution of the marine environment. Garcia and co-workers 28 developed and validated an analytical procedure for ID-SF-ICP-MS, to determine the total mass fractions of five trace elements (Cd, Cu, Hg, Pb, and Zn) and MeHg in a candidate CRM (IAEA-476) based on fish homogenate. To evaluate the measurement uncertainty of the results, they used the approach of mathematical modelling, taking into account all factors that may have an influence on the final result, in particular during the measurement step, such as isotopic equilibrium, instrumental background, spectral interferences, dead time, mass discrimination effects, and the repeatability of the measured isotope ratios.…”