A very simple and rapid method for the determination of total mercury in fish samples using the Direct Mercury Analyser DMA-80 was developed. In this system, a previously weighted portion of fresh fish is combusted and the released mercury is selectively trapped in a gold amalgamator. Upon heating, mercury is desorbed from the amalgamator, an atomic absorption measurement is performed and the mercury concentration is calculated. Some experimental parameters have been studied and optimised. In this study the sample mass was about 100.0 mg. The relative standard deviation was lower than 8.0% for all measurements of solid samples. Two calibration curves against aqueous standard solutions were prepared through the low linear range from 2.5 to 20.0 ng of Hg, and the high linear range from 25.0 to 200.0 ng of Hg, for which a correlation coefficient better than 0.997 was achieved, as well as a normal distribution of the residuals. Mercury reference solutions were prepared in 5.0% v/v nitric acid medium. Lyophilised fish tissues were also analysed; however, the additional procedure had no advantage over the direct analysis of the fresh fish, and additionally increased the total analytical process time. A fish tissue reference material, IAEA-407, was analysed and the mercury concentration was in agreement with the certified value, according to the t-test at a 95% confidence level. The limit of quantification (LOQ), based on a mercury-free sample, was 3.0 µg kg(-1). This LOQ is in accordance with performance criteria required by the Commission Regulation No. 333/2007. Simplicity and high efficiency, without the need for any sample preparation procedure, are some of the qualities of the proposed method.
A method for the determination of total mercury in fresh fish and shrimp samples by solid sampling thermal decomposition/amalgamation atomic absorption spectrometry (TDA AAS) has been validated following international foodstuff protocols in order to fulfill the Brazilian National Residue Control Plan. The experimental parameters have been previously studied and optimized according to specific legislation on validation and inorganic contaminants in foodstuff. Linearity, sensitivity, specificity, detection and quantification limits, precision (repeatability and within-laboratory reproducibility), robustness as well as accuracy of the method have been evaluated. Linearity of response was satisfactory for the two range concentrations available on the TDA AAS equipment, between approximately 25.0 and 200.0 μg kg(-1) (square regression) and 250.0 and 2000.0 μg kg(-1) (linear regression) of mercury. The residues for both ranges were homoscedastic and independent, with normal distribution. Correlation coefficients obtained for these ranges were higher than 0.995. Limits of quantification (LOQ) and of detection of the method (LDM), based on signal standard deviation (SD) for a low-in-mercury sample, were 3.0 and 1.0 μg kg(-1), respectively. Repeatability of the method was better than 4%. Within-laboratory reproducibility achieved a relative SD better than 6%. Robustness of the current method was evaluated and pointed sample mass as a significant factor. Accuracy (assessed as the analyte recovery) was calculated on basis of the repeatability, and ranged from 89% to 99%. The obtained results showed the suitability of the present method for direct mercury measurement in fresh fish and shrimp samples and the importance of monitoring the analysis conditions for food control purposes. Additionally, the competence of this method was recognized by accreditation under the standard ISO/IEC 17025.
The development and validation of a simple, reliable and fast method for the determination of cadmium and lead in fish and shrimp by GF AAS, following sample freeze-drying and tetramethylammonium hydroxide (TMAH) solubilization, is presented. The method development was achieved by sequentially applying factorial designs until optimization within the bilinear approximation of the method was accomplished.As such, seven experimental parameters were initially studied, which were considered important for the determination of cadmium and lead in seafood samples using TMAH solubilization. The validation of the method was completed in order to comply with international food regulations and method accreditation under ISO 17025. In this sense, the following parameters were evaluated: linearity, limits of detection and quantification, precision, recovery (trueness), specificity and robustness. Linearity of response was satisfactory for the concentration ranges of both analytes. The residuals for both elements were homoscedastic and independent, with normal distributions. Limits of quantification (LOQ), based on signal standard deviation for low-in-cadmium and lead samples, were 6.25 mg kg À1 and 31.25 mg kg À1 , respectively. These figures are in accordance with performance criteria required by the Commission Regulation (EU) no 836/2011. The repeatability of the method, calculated from the analysis of seven sample replicates at two concentration levels of cadmium and lead, by the same analyst, was usually better than 10%. Recovery was estimated from the repeatability evaluation, lying in the range of 84% to 99% for cadmium, and 94% to 107% for lead. Furthermore, a wide evaluation of the method robustness was performed during the method optimization. Thus, the results showed the suitability of the developed method for the determination of Cd and Pb in fish and shrimp by GF AAS, following TMAH solubilization for food control purposes. Additionally, the use of sequential factorial designs in order to achieve bilinear optimization of the method was proven to be a very valuable tool, by sharply reducing optimization time and the number of experiments.
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