Method modified AOAC 2015.01 in the microwave conditions and the addition of HCl during sample digestion for simultaneous Pb, Cd, Hg, and As in infant formula using ICP-MS: a method validation

The presence of heavy metals in infant formula has become a global concern. The most common method to determine heavy metals is AAS. However, as this technique is lacking in several aspects, including the instrument’s low sensitivity, a more sensitive instrument such as ICP-MS is necessary. The Inductively Coupled Plasma Mass Spectrometry (ICPMS) was used in accordance with the standard method AOAC 2015.01 with modifications on the microwave condition and the addition of hydrochloric acid (HCl) during the sample digestion process. The modified standard method requires a validation process. This research aimed to validate the method of analysis for the determination of Pb, Cd, Hg, As in infant formula using ICP-MS and its application in formula milk. This research consists of five stages: 1) instrumental performance; 2) homogeneity test; 3) method orientation; 4) method validation; and 5) the application of the validated method to other products. The findings in the research were: the method linearity was confirmed at working concentration 5-30 µg/kg for all the heavy metals with R2 value of nearly 1,000; the method limits of detection (LOD) were 0.74 µg/kg (Pb), 0.41 µg/kg (Cd), 0.08 µg/kg (Hg), 0.50 µg/kg (As), while the method’s limits of quantification (LOQ) were 2.48 µg/kg (Pb), 1.36 µg/kg (Cd), 0.27 µg/kg (Hg), 1.67 µg/kg (As); the method was found precise with Relative Standard Deviation (RSD) below 2/3 RSD Horwitz and all the recovery values were found to fall within the acceptable range (60–115%); the % RSD intra-lab reproducibility was below RSD Horwitz; and the method was robust, indicating that it was unaffected by small changes in its variables. The validated method can be applied routinely to determine heavy metals in infant formula and formula milk.

Determination of trace uranium in thorium matrix by laser induced fluorimetry after separation of thorium by its fluoride precipitation using NH4HF2

Thorium, a major element in thorium matrix, quenches uranium fluorescence when it is present above the ratio (Th/U) of 2000 in conventional pellet fluorimetry determination of uranium. A single step ‘sample digestion cum thorium fluoride precipitation’ with NH4HF2 has been developed for separation of bulk thorium as hydrated thorium fluoride precipitates. Uranium in aqueous solution is extracted into ethyl acetate and stripped into pyrophosphate medium (pH ∼ 7), prior to its laser induced fluorimetry determination. Optimizations of certain parameters such as the effects of fluoride flux, mineral acid, temperature and time, stripping solution, diverse ions etc. are discussed in detail. The method has been validated by analyzing a set of synthetic mixtures and certified reference materials of rock samples such as SY-2, SY-3, GSP-2, NKT-1 and CG-2 doped with a large excess of thorium. This method has been applied for the determination of microgram to nanogram uranium in thorium rich rocks and synthetic nuclear grade ThO2 with high degree of accuracy and precision. This is the improvement of the existing method which involves two liquid-liquid solvent extraction separation of thorium and uranium using the chelating agent 2,3-dihydroxynaphthalene at the different pH, compared to one solvent extraction separation of uranium in the present method, because separation of thorium by precipitation as its fluoride has already been carried out during sample digestion step itself. The proposed method involving ammonium hydrogen fluoride in combination with laser induced fluorimetry is simple, rapid, cost effective and more eco-friendly.

Assessment of Heavy Metals and Proximate Analysis of Cocoa Beans from Selected Cocoa Growing Areas in Ghana

The levels of six selected heavy metals namely: lead (Pb), cadmium (Cd), copper (Cu), manganese (Mn), iron (Fe) and zinc (Zn) have been investigated in cocoa beans sampled from Bekwai, Juaso, Kaspen, Asampaneye and Asamakese, five major cocoa-growing communities in Ghana. Aqua regia digestion procedure was applied for sample digestion and atomic absorption spectroscopy was used for the determination of the metals. The method for the determination of the metals was validated by analyzing standard reference material and levels of metals obtained compared favourably with reported values. Samples were also subjected to proximate analysis by determining moisture, ash, fibre, fat, protein and carbohydrate nutritional compositions of the beans. Method of proximate analysis as reported by Association of analytical chemists (AOAC) was used for estimation of nutritional compositions. Indeed, lead and cadmium concentrations were the lowest in all the samples. The generally high concentrations of Fe, Zn, Cu and Mn in the samples were anticipated as they are regarded essential in living organisms. The mean concentrations expressed in µg/g ranged from 0.013 to 0.042 for Pb, 25.36 to 54.24 for Cd, 36.94 to 58.71 for Zn, 7.12 to 64.65 for Mn and 10.14 to 54.17 for Cu. Proximate analysis of the cocoa beans showed carbohydrate and fat as the nutrients with the dominant composition. Correlation analysis of the metals and nutritional compositions indicated no clear relationship between the levels of the metals and the nutrients.

A general strategy for the voltammetric trace determination of tellurium in geochemical and environmental matrices after arsenic coprecipitation and critical assessment of digestion schemes

Environmental contextAmong chemical elements classified as elements of strategic importance, tellurium is rapidly becoming an emergent contaminant. There is, however, no accurate and sensitive method for measuring tellurium concentrations in environmental and geological samples (e.g., soils, sediments), and thus it is not possible to determine whether an ecosystem is being polluted by human activities. This study provides a reliable answer to this problem. AbstractA general method is proposed for the determination of tellurium in environmental and geochemical samples. Samples may be digested by any technique (acid or fusion digestion). The tellurium in the resulting solution is reductively coprecipitated with added arsenite by hypophosphorous acid, and the precipitate is redissolved and analysed by catalytic anodic stripping voltammetry. Several sample digestion techniques (acid and fusion digestions) are critically assessed. The method is applied to ore certified reference materials, with tellurium concentrations spanning three orders of magnitude, and sediment certified reference materials (ocean, lake and estuarine). An overall limit of detection (LOD) of 5 ppb is achieved. Acid digestion by H2SO4 and by HClO4 or sintering with Na2O2 in glassy carbon crucibles are shown to be the most adequate sample digestion techniques.

Metal Cations Analysis Contained in Sambucus ebulus L., by Comparative Methods of Atomic Absorption Spectrometry

The purpose of this study was to perform a comparative study of cations in the vegetative organs of Sambucus ebulus by applying three different methods of digestion before atomic absorption spectrometry. Of the tested methods, the most effective was method 3 (mineralisation with nitric acid in a microwave oven), the other methods of sample digestion leading to incomplete mineralization of the samples and implicitly to the incomplete transfer of the analytes into solution, reflecting the slightly different contents in metal cations we obtained.

Sample Digestion and Combined Preconcentration Methods for the Determination of Ultra-Low Gold Levels in Rocks

The gold abundance in basic rocks, which normally varies between 0.5 and 5 ppb, has served as a very important indicator in many geoscience studies, including those focused on the planetary differentiation, redistribution of elements during the crustal process, and ore genesis. However, because gold is a monoisotopic element that exhibits a nugget effect, it is very difficult to quantify its ultra-low levels in rocks, which significantly limits our understanding of the origin of gold and its circulation between the Earth crust, mantle, and core. In this work, we summarize various sample digestion and combined preconcentration methods for the determination of gold amounts in rocks. They include fire assay, fire assay combined with Te coprecipitation and instrumental neutron activation analysis (INAA) or laser ablation inductively coupled plasma mass spectrometry, fusion combined with Te coprecipitation and anion exchange resins, dry chlorination, wet acid digestion combined with precipitation, ion exchange resins, solvent extraction, polyurethane foam, extraction chromatography, novel solid adsorbents, and direct determination by INAA. In addition, the faced challenges and future perspectives in this field are discussed.