Certification of Marine Toxins by Quantitative NMR and Isotope Dilution MS at the Highest Metrological Level

Markus Obkircher, R&D, Merck, Buchs, Switzerland

Since the presence of marine toxins in shell fish and sea food in general is an emerging problem, fast and sensitive LC-MS methods were established very recently for food testing.^[1] Therefore, the access to well characterized reference materials for a precise and accurate quantitation of these different toxins is now a crucial need of the testing laboratories. Unfortunately, the isolation, synthesis and purification of these compounds or their stable isotope labeled analogs is very challenging and lot sizes are typically in the range of few mg.

In order to achieve certification of such small batches under ISO/IEC 17025 and ISO Guide 34 double accreditation at the highest metrological level, a combined setup of qNMR^[2],[3] and Isotope Dilution MS was successfully established.

In a first step, the concentration of a dissolved toxin is determined by a series of ¹H-HP^®-qNMR measurements. The received certified mass fraction is subsequently applied in an LC-IDMS experiment that results in a certified concentration for the stable isotope labeled analog. IDMS experiments are also carried out to determine the homogeneity and stability contribution to the overall uncertainty.

The setup was validated by the defined and well characterized system caffeine-¹³C₃-caffeine. An intra-laboratory comparison (3 persons, 3 days, 2 balances, 2 different reference solutions) of independently prepared caffeine/¹³C₃-caffeine standards and sample solutions showed an overall variation +0.2/-0.2 µg/g of the measured concentrations. After demonstration of the robustness of the method, several saxitoxin derivatives were analyzed and certified using the same methodology.

[1] M. J. Boundy et al, Journal of Chromatography A, 1387, 1-12, 2015.

[2] M. Weber, Ch. Hellriegel, A. Rueck, R. Sauermoser, J. Wuethrich, Accreditation and Quality Assurance, 18(2), 91-98, 2013

[3] M. Weber, Ch. Hellriegel, A. Rueck, J. Wuethrich, P. Jenks, Journal of Pharmaceutical and Biomedical Analysis, 93, 102-110, 2014.


Certification of Marine Toxins by Quantitative NMR and Isotope Dilution MS at the Highest Metrological Level Markus Obkircher, R&D, Merck, Buchs, Switzerland Since the presence of marine toxins in shell fish and sea food in general is an emerging problem, fast and sensitive LC-MS methods were established very recently for food testing.^[1] Therefore, the access to well characterized reference materials for a precise and accurate quantitation of these different toxins is now a crucial need of the testing laboratories. Unfortunately, the isolation, synthesis and purification of these compounds or their stable isotope labeled analogs is very challenging and lot sizes are typically in the range of few mg. In order to achieve certification of such small batches under ISO/IEC 17025 and ISO Guide 34 double accreditation at the highest metrological level, a combined setup of qNMR^[2],[3] and Isotope Dilution MS was successfully established. In a first step, the concentration of a dissolved toxin is determined by a series of ¹H-HP^®-qNMR measurements. The received certified mass fraction is subsequently applied in an LC-IDMS experiment that results in a certified concentration for the stable isotope labeled analog. IDMS experiments are also carried out to determine the homogeneity and stability contribution to the overall uncertainty. The setup was validated by the defined and well characterized system caffeine-¹³C₃-caffeine. An intra-laboratory comparison (3 persons, 3 days, 2 balances, 2 different reference solutions) of independently prepared caffeine/¹³C₃-caffeine standards and sample solutions showed an overall variation +0.2/-0.2 µg/g of the measured concentrations. After demonstration of the robustness of the method, several saxitoxin derivatives were analyzed and certified using the same methodology. [1] M. J. Boundy et al, Journal of Chromatography A, 1387, 1-12, 2015. [2] M. Weber, Ch. Hellriegel, A. Rueck, R. Sauermoser, J. Wuethrich, Accreditation and Quality Assurance, 18(2), 91-98, 2013 [3] M. Weber, Ch. Hellriegel, A. Rueck, J. Wuethrich, P. Jenks, Journal of Pharmaceutical and Biomedical Analysis, 93, 102-110, 2014.

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