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Glycerine Analysis
Published in Eric Jungermann, Norman O.V. Sonntag, Glycerine, 2018
The most common method for measuring arsenic content uses silver diethyl-dithiocarbamate as a colorimetric reagent. Food Chemical Codex and USP require wet-ashing the sample before the colorimetric analysis is performed. CTFA specifies diluting the sample without wet-ashing and proceeding directly to the color-generating step. Wet-ashing destroys organic matter and converts arsenic to the arsenic (V) oxidation state without loss of volatile arsenic compounds, which would occur if the sample were ashed at muffle oven temperatures. About 1 g of glycerine is digested with sulfuric acid until charring begins. Thirty percent hydrogen peroxide is added, very slowly and carefully at first, to prevent too violent a reaction. Oxidizing conditions are maintained by adding more peroxide whenever the solution becomes dark. When oxidation is complete, the temperature is increased until copious fumes of SO3 evolve. Then, the sample is cooled, water is added and the solution is fumed again to remove traces of hydrogen peroxide.
Sample Preparation Techniques
Published in Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus, Environmental Chemical Analysis, 2018
Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus
Oxidation of organic matter is an important part of the digestion process. HClO4, HF and H2O2 are good for samples that are more difficult to oxidize. If a sample contains large amount of organic matter (e.g., sewage sludge) the sample may be dry ashed. In the dry ashing process, the sample is evaporated to dryness, then heated in a furnace at high temperature until it forms white ash. The ash is extracted with HNO3. Care should be taken that volatile metals are not lost during the ashing process.
Determination of Metals in Non Saline Sediments
Published in T. R. Crompton, Determination of Metals and Anions in Soils, Sediments and Sludges, 2020
Add 35 mL concentrated nitric acid and 5 mL 30% hydrogen peroxide to 5–10g of sample in a beaker and evaporate to dryness on a hot plate. Ash at 400–425 °C for 1 h in a muffle furnace and cool. Add 25 mL of acid mixture (200 mL concentrated nitric acid, 50 mL concentrated hydrochloric acid and 750 mL deionised water), 20 mL 10% ammonium chloride and 1 mL Ca(NO3)24H2O (11.8g/100mL). Heat gently for 15 min and cool for at least 5 min. Separate the residue by filtration or centrifugation, wash the residue twice with deionised water, and combine washings and extract in a 250 mL volumetric flask and adjust to volume with demineralised water. The mean concentration of four replicate analyses for the major constituents by each of the six analytical procedures is presented in Table 3.27. Similar data for minor constituents are in Table 3.28. The ashing procedure was used as a reference point to determine the relative recoveries of trace metals because trace metal concentrations recovered by the ashing procedure approach their total concentration in the sediments. Tables 3.29 and 3.30 present data showing the mean recovery and standard deviation from the mean of major and minor sediment constituents relative to the total amount present and to the concentrations as determined by the nitric acid dry ashing digestion, respectively. Note that the pH7 citrate-dithionite and the 25% acetic acid extractions recovered significantly less of all constituents than the 0.3 mol L−1 hydrochloric acid and pH 3 citrate-dithionite procedures. Examination of the data in Table 3.30 indicates that 0.3 mol L−1 hydrochloric acid recovers more zinc and less cadmium, chromium and cobalt than the pH 3 extract. There is no difference in the recovery of copper, nickel and lead by either procedure. Table 3.31 indicates that this relationship is generally valid for samples of widely varying particle size distribution.
Review of cigars and cigar-type products as potential sources of consumer exposure to heavy metals
Published in Journal of Environmental Science and Health, Part C, 2022
Paweł Jacek Hać, Bartłomiej Michał Cieślik, Piotr Konieczka
Menden et al. in 1972 published the results of an analysis of the content of cadmium, nickel, and zinc in cigarettes, which they compared with the content of these elements in pipe and cigar tobacco. As reported, they used one brand of cigar, purchased on the market. The country of origin of this cigar is unknown; however, research has been conducted in the United States. Tobacco samples were prepared for testing using dry and wet ashing. No significant differences were observed in the results obtained using these two methods. Wet ashing consisted of boiling the samples until dissolution and oxidation in concentrated HNO3, evaporating to a volume of 1 ml and then dissolving with hot 10% HNO3 for analysis. Dry ashing was performed by placing samples wetted with concentrated nitric acid (V) in a muffle furnace (400–450 °C). What remained was dissolved in 2 ml of concentrated HNO3, evaporated, and the residue was dissolved in 10% HNO3 for analysis, which was performed with 10% nitric acid solutions (V) using atomic absorption spectroscopy (AAS) by aspirating samples directly into a Perkin-Elmer Model 303.28