Acid digestions, wet

Three alternate techniques yielded quantitative recovery of cadmium from various matrices acid digestion (wet oxidation), ashing in the presence of sulfuric acid (wet ash), and a scaled down wet ashing procedure (mini-ash). The mini-ash technique is designed for small samples and is well suited for HVAA analysis. 

The Cr203 content of each catalyst was determined by atomic absorption spectroscopy (Varian/Spectr AA-20 plus) on acid-digested samples. Total surface areas were determined by a single point BET method (nitrogen adsorption-desorption at 77.5 K) using a mixture of 29.7% N2 in helium. Samples were wet-loaded into the flow tube and dried at 423 K in a hydrogen flow for 15 minutes and then for another 30 minutes at 513 K before cooling in helium. 

Organic carbon can be determined in calcareous soils after the carbonates have been removed by treatment with sulphuric acid-iron(II) sulphate solution and the samples oven-dried at 105°C. However, as in all other wet-combustion methods, chloride ions interfere [7]. Interference from small amounts of chloride ions (up to 4mg of Ch as KC1 or NaCl) was reduced by adding 2.5% of mercury II oxide or silver I sulphate to the acid digestion mixture. 

Acid digestion systems for wet digestions System 6/20 System 12/40 Tecator AB Box 70... 

The laboratory sample is usually dissolved for analysis. It is important to dissolve the entire sample, or else we cannot be sure that all of the analyte was dissolved. If the sample does not dissolve under mild conditions, acid digestion or fusion may be used. Organic material may be destroyed by combustion (also called dry ashing) or wet ashing (oxidation with liquid reagents) to place inorganic elements in suitable form for analysis. 

The effectiveness of mixed perchloric and nitric acids in wet oxidation of a wide range of organic materials has been studied. Violent oxidation occasionally occurred, but addition of sulfuric acid prevented any explosions or ignition during digestions... 

Evans et al. [98] has described a method for the determination of total copper, iron, manganese and zinc in various plant materials. Organic matter is destroyed by wet oxidation and measurement is made directly upon the sulfuric acid digests by flame atomic absorption spectrophotometry. In the measurement, direct interferences from the inorganic species found in plant... 

A number of procedures for the determination of metals and biological samples call for the extraction of the metal with an organic chelating agent in order to remove interferences and concentrate the metal to enable detection of low levels. The urine or blood sample may be first subjected to wet ashing to enable extraction of the metal. Beryllium from an acid-digested blood or urine sample may be extracted by acetylacetone into methylisobutyl ketone prior to atomic absorption analysis. Virtually all of the common metals can be determined by this approach using appropriate extractants. 

A comparison of different mineral acids for wet digestion of plant material for AAS analysis was carried out by Dokiya et al. (1975), who concluded that nitric acid was best for the determination of Cu, Mn and Pb by flameless AAS, whereas a nitric sulphuric mixture was best for Fe, Mn, Cu and Zn by FAAS. Most literature reports dissolve plant material in nitric acid (Middleton and Stuckey, 1954) or in nitric and perchloric acids (Isaac and Johnson, 1975 Williams, 1978, Thompson and Wood, 1982). This method will not dissolve aluminium containing particles from soil or other contaminations (Pierson and Evenson, 1988 Ramsey et al., 1991) (see also Standard Reference Materials). 

Molybdenum. Molybdenum can be analyzed by P CAM 173 for total Mo, by S-193 (12) for soluble Mo, or by S-376 for insoluble Mo. The standard nitric wet ashing used in P CAM 173 does not distinghish between soluble and insoluble Mo which have OSHA standards of 5 mg/cu m and 15 mg/cu m. Nitric acid digestion may not dissolve some insoluble Mo that require nitric/perchloric acid or base/nitric acid depending on the solubility properties. Soluble Mo compounds are hot water leached from the cellulose membrane filter used in all three methods. A fuel-rich air/acetylene flame used in P CAM 173 is replaced by an oxidizing nitrous oxide/acetylene flame to achieve total atomization of Mo as detected at 313.3 nm. Aluminum and traces of acid enhance the Mo flame response therefore, 400 ppm A1 is added to the final solution of both S-193 and S-376 and 0.1 N nitric acid is added to the water leach-soluble Mo final solution, S-193. 

Yttrium. After initial nitric acid wet ashing, the Y is 2 1 nitric sperchloric acid digested. The resulting Y O /CIO ) are solublized with 5 ml of 0.6 M HC1 containing 1000 ppm Na. This solutionis aspirated into a reducing nitrous oxide-acetylene flame at 410.2 nm. The reducing flame and Na are used in S-200 to minimize Y ionization in the flame. Al, K, and phosphoric acid depress the Y absorbance in the flame however, 1000 ppm Na minimizes these interferences. 

Oxidative decomposition by wet ashing is the most widely used sample preparation method for milk samples. Acid digestion involves the use of mineral acids and oxidizing agents to dissolve the sample. Some of the acids commonly used in these procedures are HC1, HNO3, H2S04, and HCIO4. Wet decomposition can be performed with either open or closed systems. Open systems entail... 

Oliver [190] recommends the dissolution of the polymer if possible (see above) but in other cases a wet ashing procedure was used. The sample was heated with 2—3 ml of concentrated sulphuric acid and then hydrogen peroxide added drop-wise until the organic matter was destroyed. Twenty elements were determined in a 2% solution of polymer. Polymers may be dispersed in an organic solvent and trace metals removed by leaching with an appropriate aqueous solution, preferably the procedure should be repeated more than once to ensure complete extraction. To determine antimony in fire-retardant polypropylene, the sample was dispersed in xylene and extracted with 6M hydrochloric acid under reflux [191]. The filtered acid layer was combined with two further extracts prior to aspiration into the air/acetylene flame and measurement at 217.6 nm. Martinie and Schilt [45] reported that nylon would dissolve completely in perchloric/nitric acid digestion but potentially explosive problems were encountered in the dissolution of Amberlite resins and rubber. 

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