Dissolution of the sample

The metal or alloy does not dissolve completely analyse the filtrate as described in Section 5.7. Examine the insoluble residue according to Section 

If the alloy resists the action of aqua regia, fuse it with sodium hydroxide pellets in a silver dish or crucible (CAUTION USE A FUME CUPBOARD). When decomposition is complete, allow to cool, transfer the silver vessel to a beaker and extract the melt with water with gentle heating. Remove the silver vessel from the beaker. Strongly acidify the contents of the beaker with 8m nitric acid, evaporate to dryness on a water bath and proceed as above. Note that the silver vessel will be attacked during this procedure thus do not test for silver in the melt. 

The composition of some common alloys are given below the chief constituents are listed in their order of mass per cent  

Phosphor bronzes Solders Pewter Type metals 

Monel metal Constantan Nichrome Manganin Wood s alloy Rose s alloy 

6 DISSOLUTION OF THE SAMPLE The preliminary tests, described in the previous sections, have already revealed whether the substance is soluble in water or in acids. If such information is not available, the following procedure should be adapted. 

When a suitable solvent has been found, the solution for analysis is prepared with 0-5-1 g of the solid the volume of the final solution should be 15-20 ml. 

If the substance is insoluble in aqua regia (and in concentrated acids), it is regarded as insoluble and is treated by the special methods detailed in Section V.7 below. 

If the sample is a metal, the procedure described in Section V.3 should be adopted. The insoluble part, if any, should be treated according to Section V.7. 

Unless the sample is readily soluble in water, the solution is unsuitable for testing for anions, as during dissolution in acids some of these might decompose. For the test for anions we can use either the aqueous solution, or, if the sample is not soluble in water, sodium carbonate extract should be prepared either from the whole of the sample, or the sample should first be extracted with hot water and the residue treated with sodium carbonate. This procedure is described in detail in Section V.18. 

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MetaUic impurities in beryUium metal were formerly determined by d-c arc emission spectrography, foUowing dissolution of the sample in sulfuric acid and calcination to the oxide (16) and this technique is stUl used to determine less common trace elements in nuclear-grade beryUium. However, the common metallic impurities are more conveniently and accurately determined by d-c plasma emission spectrometry, foUowing dissolution of the sample in a hydrochloric—nitric—hydrofluoric acid mixture. Thermal neutron activation analysis has been used to complement d-c plasma and d-c arc emission spectrometry in the analysis of nuclear-grade beryUium. 

Total carbon in beryUium is determined by combustion of the sample, along with an accelerator mixture of tin, iron, and copper, in a stream of oxygen (15,16). The evolved carbon dioxide is usuaUy measured by infrared absorption spectrometry. BeryUium carbide can be determined without interference from graphitic carbon by dissolution of the sample in a strong base. BeryUium carbide is converted to methane, which can be determined directly by gas chromatography. Alternatively, the evolved methane can be oxidized to carbon dioxide, which is determined gravimetricaUy (16). 

Elemental analysis of organie and inorganie samples requires partial or total dissolution of the sample prior to speetrometrie analysis. Mierowave-assisted extraetion (MAE) provides an alternative to traditional digestion methods and it is reeognized as one of the most effieient methods for the dissolution of soil samples. 

Edwards e/a/. carried out controlled potential, slow strain-rate tests on Zimaloy (a cobalt-chromium-molybdenum implant alloy) in Ringer s solution at 37°C and showed that hydrogen absorption may degrade the mechanical properties of the alloy. Potentials were controlled so that the tensile sample was either cathodic or anodic with respect to the metal s free corrosion potential. Hydrogen was generated on the sample surface when the specimen was cathodic, and dissolution of the sample was encouraged when the sample was anodic. The results of these controlled potential tests showed no susceptibility of this alloy to SCC at anodic potentials. 

Fig. 6-1. Changes in the UV spectrum during the (Z)/(F)-isomerization of N-(4-nitrophenyl)-S-(4 -tolyl)diazosulfide in ethanol. Numbers of the curves refer to time (in min.) after dissolution of the sample. (From Yamada, 1970.)...

Vacuum sublimation is a very popular method for purification of organometallic compounds, because it is so convenient and easy. The sublimation process is not very selective, however, so that it is seldom possible to separate cleanly more than one or perhaps two compounds from a mixture, while in many cases several compoimds occur simultaneously in the irradiated targets. Moreover, annealing may be induced by the heating of the sample for sublimation, although this can be minimized by prior dissolution of the sample to release reactive atoms and... 

Sublimation without prior dissolution is likely to cause thermal annealing eflFects. Even dissolution of the samples at room temperature may cause thermal reactions to occur, although these, at least, are usually reproducible. 

Exchange and other spurious reactions are often difficult to avoid. Carriers, scavengers, and the like should be added to the solvent before dissolution of the sample. Even then exchange is possible. 

Silica gel or alumina is usually used as the stationary phase. For these active phases a solvent of weak elution power is recommended for dissolution of the sample. A... 

The polymer/additive system in combination with the proposed extraction technique determines the preferred solvent. In ASE the solvent must swell but not dissolve the polymer, whereas MAE requires a high dielectric solvent or solvent component. This makes solvent selection for MAE more problematical than for ASE . Therefore, MAE may be the preferred method for a plant laboratory analysing large numbers of similar samples (e.g. nonpolar or polar additives in polyolefins [210]). At variance to ASE , in MAE dissolution of the polymer will not block any transfer lines. Complete dissolution of the sample leads to rapid extractions, the polymer precipitating when the solvent cools. However, partial dissolution and softening of the polymer will result in agglomeration of particles and a reduction in extraction rate. 

XRD analyses were performed on oriented samples prepared by spreading of the sample suspension on a glass slide, followed by drying at room temperature. The XRD patterns were obtained with a PW 1130/00/60 Philips diffractometer using CuKa radiation (/, = 1,5405 A). Chemical analysis was carried out on a Perkin Elmer 3100 atomic absorption spectrometer after dissolution of the sample with several acids (HF, HCIO4, HC1) for 24h, and HN03 in a second time. 

Sample preparation requires only dissolution of the sample to a suitable concentration in a mixture of water and organic solvent, commonly methanol, isopropanol, or acetonitrile. A trace of formic acid or acetic acid is often added to aid protonation of the analyte molecules in the positive ionization mode. In negative ionization mode ammonia solution or a volatile amine is added to aid deprotonation of the analyte molecules. 

Pressure dissolution and digestion bombs have been used to dissolve samples for which wet digestion is unsuitable. In this technique the sample is placed in a pressure dissolution vessel with a suitable mixture of acids and the combination of temperature and pressure effects dissolution of the sample. This technique is particularly useful for the analysis of volatile elements which may be lost in an open digestion [24]. 

In sample preparation or sample pretreatment steps there are a number of important operations that may include dissolution of the sample, transformation of the elements into specific inorganic forms, conversion of the... 

Dissolution of the sample is the method required in a number of spectroscopic and chromatographic techniques (e.g., UV-Vis spectrophotometry, atomic absorption spectroscopy (AAS), high performance liquid chromatography (HPLC), and thin-layer chromatography (TLC)). Selection of the suitable solvent is essential... 

Determination of Mg in the hard tissues (shell and pearl) of shellfish by the ICP-AES method involves dissolution of the sample by hot concentrated nitric acid, hydrochloric acid and perchloric acid. However, the large excess of Ca in the matrix strongly interferes with the end analysis and causes damage to the torch. After adjusting the pH to 4.5, the Mg ions were extracted by a 0.01 M solution of 3-methyl-l-phenyl-4-trifluoroacetylpyrazol-5-one (16) in dibutyl ether and the ICP-AES analysis was carried out by direct injection of the organic solution. ... 

Before the extraction procedure may commence, the sample must be prepared in such a way that it is in a condition for extraction of the analyte(s). For analyzing sulfonamide residues in liquid samples such as milk, a pretreatment dilution step with water prior to direct fluorometric detection may be required (207). Dilution of milk with aqueous buffer (208) or sodium chloride solution (209) prior to sample cleanup has also been reported. For the analysis of honey a simple dissolution of the sample in water (210, 211) or aqueous buffer (212) is generally required. Semisolid samples such as muscle, kidney, and liver, require, however, more intensive sample pretreatment. The analyte(s) must be exposed to extracting solvents to ensure maximum extraction. The most popular approach for tissue break-up is through use of a mincing and/or homogenizing apparatus. Lyophilization (freeze-drying) of swine kidney has been carried out prior to supercritical-fluid extraction of trimethoprim residues (213). 

The reaction of DCIP with ascorbic acid is shown in Figure El 1.3. Ascorbic acid reduces the indicator dye from an oxidized form (red in acid) to a reduced form (colorless in acid). The procedure is simple, beginning with dissolution of the sample to be tested in metaphosphoric acid. An aliquot of the sample is then titrated directly with a solution of DCIP. Although the original DCIP solution is blue, it becomes light red in the acid solution. Upon reaction with ascorbic acid in the sample, the dye becomes colorless. Titration is continued until there is a very slight excess of dye added (faint pink color remains in the acid solution). 

The level can be confirmed by a standard dibutyl amine titration. A typical method is given in Appendix 6. Depending on the type of isocyanate used, the exact solvent for dissolution of the sample may have to be determined. 

A novel approach was described for the speciation analysis of Hg, namely methyl-Hg and Hg(II), in Fsh tissue using GC-MIP-AES [36]. Focused MW-assisted digestion was applied for sample preparation (tissues were dissolved with TMAH, 25 percent aqueous solution), a technique which enables mild, quick, and complete dissolution of the sample. The method was validated by analysis of the BCR 464 freeze-dried tuna E>sh CRM. 

A rapid and simple MW-assisted digestion method with alkaline solution (TMAH or methanolic KOH solution) was developed for speciation analysis of inorganic Hg and methyl-Hg in biological tissues [41]. Extracts with quantitative recoveries of Hg species after the alkaline dissolution of the sample were directly analyzed by an automated on-line hyphenated system incorporating aqueous HG, cryogenic trapping, GC, and detection by A AS. The proposed method was validated by the analysis of biological CRMs (CRM 463, DORM-1, TORT-1) and one BCR sample from an interlaboratory study (Tuna Fish 2). 

Dissolution of the Sample Material, Extraction and Separation of Hg Species... 

All the solid phases were identified and characterized for crystallinity by X-ray powder diffraction (Philips PW 1730/10 diffractometer, Cu Kq radiation equipped with a PW 1030/70 vertical goniometer and connected to a P.C. computer for quantitative analyses). Crystallinities for Nu-10 and cristobalite were computed by comparing the intensity of the most characteristic diffraction peaks of each sample to that of the corresponding pure 100% crystalline phases used as standards. In some cases calibration curves derived from Nu-10/cristobalite mechanical mixtures were used. Si, Al, and alkali contents were determined either on precursors or calcined samples (900 C, air flow, 4h) by atomic absorption, using a Perkin-Elmer 380 AA instrument after digestion and dissolution of the samples in H,S04/HF solutions and further elimination of HF by gentle heating at 60 C for 12 n. 

Sodium analyses were carried out by flame photometric methods after dissolution of the sample in HF. X-ray diffraction was carried out on standard powder diffraction equipment. 

VIII.3 SYSTEMATIC ANALYSIS. GENERAL CONSIDERATIONS In this abbreviated course of qualitative analysis students should try to analyse dissolved samples provided by the teacher. In the present chapter it is assumed that a solution is to be analysed, which may contain the ions discussed in Section VIIL2. If it is felt desirable to carry out analyses of solid samples, the preliminary tests on and dissolution of the sample should be carried out according to Sections V.I to V.3 and V.5 to V.7. In such a case the preliminary tests described under Section VIII.4 need not be repeated, but the student may continue with Section VIII.5, always keeping in mind the results of the preliminary tests. 

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