Acid digestion method

Methods for iodine deterrnination in foods using colorimetry (95,96), ion-selective electrodes (94,97), micro acid digestion methods (98), and gas chromatography (99) suffer some limitations such as potential interferences, possibHity of contamination, and loss during analysis. More recendy neutron activation analysis, which is probably the most sensitive analytical technique for determining iodine, has also been used (100—102). 

Pinho, J., J. Canario, R. Cesario, and C. Vale. 2005. A rapid acid digestion method with ICP-MS detection for the determination of selenium in dry sediments. Anal. Chim. Acta 551 207-212. 

Atomic absorption has become the primary method for determining metal concentrations in industrial hygiene samples. The types of samples that can be analyzed in AAS will be discussed along with acid digestion methods and AAS atomization techniques. No attempt will be made to thoroughly review the theory... 

The chemical compositions of the ancient Egyptian Blue samples (reported in the following section) were determined by atomic absorption spectrophotometry using the hydrofluoric acid digestion method together with the lithium metaborate fusion method for the silica determination (9). Some 20-30 mg of powder drilled from the objects was used for these analyses. Additionally, the arsenic concentrations were determined by x-ray fluorescence spectrometry. The precision of the analytical data was 1-2% for the major elements (>10% concentration) and deteriorated to 5-20% for the trace elements (<0.1% concentrations). However, due to the inhomogeneity of the material, variations in elemental concentrations (i.e., major, minor, and trace) of 10-15% can be expected within a single object. 

Sample Preparation Using Microwave Acid Digestion Method... 

To monitor these concentrations of stabilisers for precise, accurate measurements a method must be available that must detect levels as low as 600 ngg-1 and as high as 5000 ngg-1. The allowed tolerance can vary between 20% for low levels to 10% for higher levels without affecting the performance of the product. The lower concentration would be expected to cure faster than those containing higher concentrations of stabiliser. The different level of stabiliser is dictated by the application of these adhesives and must be formulated under very controlled conditions. ICP-OES is an ideal tool to monitor the metal type stabilisers using sample dilution, bomb combustion or microwave acid digestion methods. 

The correct choice of sample preparation and analysis will give excellent confidence in the reported results. Microwave acid digestion methods can be used to prepare almost all... 

Example 5.2 Total Metal Analysis of Soil Using X-Ray Fluorescence Spectroscopy - Comparison with Acid Digestion (Method 3050B), followed by Flame Atomic Absorption Spectroscopy... 

Kacprzak, J.L and Chvojka, R. (1976) Determination of methyl mercury in fish by flameless atomic absorption spectroscopy and comparison with acid digestion method for total mercury. J. Assoc. Off. Anal. Chem., 59,153-157. 

Iodine concentration was determined using a modification of the chloric acid digestion method described by Benotti and Benotti for serum. The iodine content of mothers nulk is shown in Table 50.3. Seventy-six percent of the samples had an iodine concentration between 10 and 30p,g/100ml. No statistically significant differences were found between samples of women with premature and term delivery, or between different times during the lactation period. Mean values for the iodine content of breast milk are quite variable. Breast milk is the best source of iodine for the newborn baby. 

PP is the total phosphorus associated with particulate matter. Total phosphorus in the particulate matter is determined by either wet ashing or perchloric acid digestion methods. PP often includes inorganic forms such as phosphate sorbed onto suspended clay particles, and suspended crystalline and amorphous precipitates of PO with Ca, Mg, Al, and Fe. Inorganic phosphorus associated with PP is termed as PIP. Particulate matter is extracted with 1M HCl and filtered solutions are analyzed for orthophosphate as described above. 

Direct AP methods involve the determination of citrate-soluble P2O5 by direct AP analysis after the water-soluble portion is removed. The failure to remove the water washing step before addition to the neutral ammonium citrate will result in oversaturation of the ammonium citrate, resulting in low results. Generally, direct methods are less precise and results have a higher standard deviation. Problems encountered with direct methods are technique, interference of ammonium citrate in the spectrophotometric method, and not using proper acid digestion methods. 

Precondition for a voltammetric determination of trace elements in urine is a sample pretreatment. The problem of losses of mercury with classic mineralization methods is described above. To avoid this problem, the authors have developed an acid digestion method with the addition of thioacetamide. All mercury in the sample is converted by this to the extremely poorly soluble mercury sulfide (HgS), which is stable under the conditions chosen. Subsequently hydrogen peroxide is added to oxidize the HgS and liberate the Hg ion [113]. 

Perz, R.C., van Lishaut, H., Schwack, W. (2000) CS2 bhnds in Brassica crops false positive resnlts in the dithiocarbamate residue analysis by the acid digestion method. Journal of Agricultural and Food Chemistry, 48,792-796. 

The crystallinity values (138) obtained with the fuming nitric acid digestion method for the copolymers synthesized with a Ti-containing system (r,r2 = 1.5) are slightly higher 75% for 3.4% of butene-1 and 44% for 13.7% of butene-1 in the copolymers. 

In comparison with the acid digestion method, the hydrogenation method is more susceptible to matrix interferences. Two types of interferences are possible. Samples containing zinc, cadmium or mercury cannot be analyzed, as the high volatility of these elements results in the formation of a metallic mirror on the cooler parts of the tubing, which partially or completely absorbs the released sulphide. Sulphur may also be retained in the sample because it is present in the form of sulphur compounds which are not reduced or decomposed, e.g. manganese sulphide, or is held in crystal lattices which do not allow sufficiently rapid diffusion of sulphur at the temperature of 1150°C. 

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