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Robuustheidsbepaling L-cysteïne toevoeging t.b.v. totaalkwikbepaling met Instrumentele Neutronen Activeringsanalyse

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Robuustheidsbepaling L-cysteïne toevoeging t.b.v. totaalkwikbepaling met Instrumentele Neutronen Activeringsanalyse

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This paper describes the robustness determination and optimization of L-cysteine addition for total mercury content determination by Instrumental Neutron Activation Analysis (INAA).
Instrumental Neutron Activation Analysis is an analysis technique to measure concentrations of chemical elements regardless of their chemical and physical state. Samples are being irradiated with neutrons originating from a nuclear reactor. After capturing a neutron, the atom becomes instable and emits different kinds of radiation, of which gamma radiation is one. Semi-conductor spectrometers are used to measure these gamma-rays. INAA has shown to be sensitive enough to quantify mercury, however loss of mercury takes place during irradiation. Previous research has shown that adding L-cysteine to DORM-2 reference material eliminates mercury content loss. This occurs during irradiation which leads to heating of samples. The result is evaporating of volatile methyl mercury. This outcome has not been shown in different matrices or other sample preparation and measurement parameters. In the current method no extra procedure is performed to reduce Hg loss. Hence, recoveries of around sixty percent were determined for mercury content determination.
In order to meet the necessity of adding mercury content determination in samples to the multi-element analysis, an existing method was expanded.
Element calibration of mercury on all laboratory of INAA spectrometers was planned to be carried out. However due to long-term adjustments to the NPT spectrometer and faulty neutron source, the calibration is yet to be executed.
The influence of irradiation time on the loss of mercury was determined. This was found to be instantaneous, meaning that already at the minimum amount of time which is available at the neutron source, the measured mercury content was too low as compared to the certified value. Without addition of L-cysteine, therefore, methyl mercury in a reference material or sample cannot be determined reliably.
The powder solution with crushed L-cysteine powder added during sample preparation led to the best results. Attempts to omit several steps of this method contributed to lower measured mercury content i.e. more loss of mercury.
Using too little L-cysteine for the powder solution method can also likewise lead to less containment of mercury content. Adding a small amount of L-cysteine on top of and underneath samples does not suffice, its outcome is lower measured mercury content, especially when the total amount of mercury consists of methyl mercury, such as in animal tissue. After thorough literature research, coating the used sample capsules with L-cysteine was deemed too impractical, expensive and therefore not an option.
Surrounding samples with L-cysteine blanks in the irradiation facilities has not led to the expected effect: lost mercury originating from the nearby samples did not get trapped in the blanks. This approach therefore was found not to be an option.
The used L-cysteine was tested for impurities and its effects on the multi-element analysis. Traces of several elements were found to be present. However these small traces did not have a negative influence on the content determination of the multi-element analysis.
The addition of the L-cysteine powder mixture for routine determination of mercury content is robust enough to be implemented and a candidate for method calibration and validation.

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OrganisatieHogeschool Leiden
OpleidingChemie
AfdelingFaculteit Techniek
PartnersReactor Instituut Delft
Datum2016-11-22
TypeBachelor
TaalNederlands

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