Dissolution of samples

Suitable inlets commonly used for liquids or solutions can be separated into three major classes, two of which are discussed in Parts A and C (Chapters 15 and 17). The most common method of introducing the solutions uses the nebulizer/desolvation inlet discussed here. For greater detail on types and operation of nebulizers, refer to Chapter 19. Note that, for all samples that have been previously dissolved in a liquid (dissolution of sample in acid, alkali, or solvent), it is important that high-purity liquids be used if cross-contamination of sample is to be avoided. Once the liquid has been vaporized prior to introduction of residual sample into the plasma flame, any nonvolatile impurities in the liquid will have been mixed with the sample itself, and these impurities will appear in the results of analysis. The problem can be partially circumvented by use of blanks, viz., the separate examination of levels of residues left by solvents in the absence of any sample. 

A reverse-phase HPLC assay, as part of the Association of Official Analytical Chemists report on analysis of fat-soluble vitamins, was described by DeVries et. al. (65). Analysis were made with a Merck LiChrosorb RP-18 column (Manufacturing Chemists, Inc., Cincinnati, OH) and a acetonitrile propionitrile water (79 15 6) mobile phase. Although adequate chromatography was realized, the authors were concerned that problems arose concerning influence of temperature, dissolution of sample and purification of solvents in the mobile phase. For these reasons they recommended normal-phase chromatography. Separation of vitamins D2 and Dj with their systems was not discussed. 

Species distribution studies have shown that trace element (e.g. metals) concentrations in soils and sediments vary with physical location (e.g. depth below bed surface) and with particle size. In these speciation studies the total element content of each fraction was determined using a suitable trace element procedure, for example, solid sample analysis by X-ray emission spectroscopy or neutron activation analysis, or alternatively by dissolution of sample and analysis by ICPOES, AAS or ASV. The type of sample fraction analysed can vary, and a few... 

In a M solution of a strong monobasic acid (supposing that the dissociation is complete) the hydrogen-ion concentration is 1 mol -1. On the other hand, in a M solution of a strong monovalent base the hydroxyl-ion concentration is lmol -1, thus the hydrogen-ion concentration is 10"14 mol C-. The hydrogen-ion concentration of most of the aqueous solutions dealt with in chemical analysis (other than concentrated acids, used mainly for dissolution of samples), lies between these values. 

Three approaches to the automation process can be distinguished, taking into account the criterion of the flexibility of the automation device [2], The first, denoted as flexible, is characterized by the possibility of adaptation of the instruments to new and varying demands required from the laboratory examples of these instruments are robots. The second approach, denoted as semiflexible, involves some restrictions for the tasks executed by the instrument the tasks are controlled by a computer program and its menu. As examples, autosamplers or robots of limited moves can be given. In the third approach, the instruments can execute one or two tasks, without feasibility of new requirements as examples, supercritical fluid extractors or equipment for dissolution of samples can be given. 

Dissolution of sample Extent of dissolution to fit calibration range, or limit of detection Complex formation, extraction, wet digestion, dry ashing, fusion, combustion... 

Hydrofluoric acid finds occasional use in conjunction with other acids in attacking steels that dissolve with difficulty in other solvents. Because hydrofluoric acid is extremely toxic, dissolution of samples and evaporation to remove excess reagent should always be carried out in a well-ventilated hood. Hydrofluoric acid causes serious damage and painful injury when brought into contact with the skin. Its effects may not become evident until hours after expo.sure. If the acid comes into contact with the skin, the affected area should be immediately washed with copious quantities of water. Treatment with a dilute solution of calcium ion, which precipitates fluoride ion, may also be of help. 

Dunlop EC (1961) Decomposition and dissolution of samples organic. In Kolthoff IM, Elving PJ and Sandell EB, eds. Treatise on analytical chemistry. Part I (Theory and practice), Vol 2, section C. Separation principles and technics (LB Rogers, section advisor), pp. 1051-1094. Interscience Publishers, New York. 

In most cases, the solubility of a metal dramatically increases by heating the acid. To improve the dissolution of samples in hot acids, a device often referred to as a digestion bomb has been developed. This device is comprised of a Teflon-lined... 

The widespread use of microwaves for dissolution of samples is gradually replacing the conventional pressure reactors. This is particularly true in the determination of inorganic and organic analytes. Sample dissolution can be conducted in both closed and open systems. 

The catalysts chemical composition was analyzed by EDAX method (JEM-35CF SEM, Jeol Co. Japan) excluding Li, which was detected by atomic adsorption spectrometry (Varian Spectrometer AA 375) after dissolution of sample. The catalysts surface area was measured (BET method, ASTM D3663-84). 

The polymers may be introduced into the chromatographic column as powders of appropriate particle size, as in the case of melting transition, thus avoiding the preceding dissolution of samples. The retention diagrams recorded with powders of poly(vinyl chloride) [153], polyacrylonitrile [200] and polybutadiene [207] assume exactly the shape in Figure 5.13. This aspect is useful in the case of semi-crystalline polymers, block copolymers with incompatible blocks, and fibres [176] because it makes possible the study of the effect of thermal treatment on the transitions. 

The first critical step in TLC is the sample application. It is well-known that circular chromatography phenomena may occur when manual spots are applied (6), especially if the volume is too large or if an unsuitable solvent for the layer adsorption has been used due to its choice for the dissolution of samples. Such phenomena induce spot diffusion. Location errors can then be observed when detection is performed by a classical scanner. For example, a systemic position error of 0.1 mm for each spot produces a final location error of 1.0 mm at the 10th spot. Such a variation is not acceptable for quantitative postchromatographic evaluation. To prevent this, the most suitable laboratory equipment should combine sample application and densitometry within the same mechanical system. The automatic spraying system for sample applications is equipped with a microprocessor (7), which ensures very reproducible repetitive applications, (Figure 1). It also allows the selection of the application speed and the form of application as a spot or a narrow band. 

Solvents. Reagent grade toluene and 95% ethanol were used for fractionation without further purification. Spectroscopic grade benzene was used as the solvent in sample-deposition solutions. Inasmuch as the OTMS reacts rapidly with moisture, all traces of water should be removed from the benzene prior to its use for this purpose. To this end, the benzene used for dissolution of samples C, CDS-B-4, D-1, D-2, and D-3 was first refluxed over calcium hydride and distilled to remove any residual water. A less stringent procedure was employed for samples A and B. 

The EAS of the melts recorded during the anodic dissolution of samples of AISI 316L steel subjected to a prior annealing are given in Figure 6.5.7. 

Dissolution of sample requires > 10% acetonitrile. This purification is still possible using multiple injections through a large injection loop. Inject only 10% of the loop volume at a time. Add the sample to the loop fairly rapidly to cause mixing in the loop, and then quickly inject onto the column. Do not allow the sample to sit in the loop since precipitation may occur. Allow extra time between injections to ensure that the sample is bound well to the column. 

Simple steps such as dissolution of samples in a suitable solvent (or mixture), filtration or centrifugation, evaporation of solvent, distillation, etc. 

Isotope dilution analysis with the SSMS can be used with almost all of the polynuclidic elements. Accuracies of 5-10 % are obtained on 0.1-1 /ig of a trace element using photographic detection better accuracies should be obtainable with electronic detection. Analysis of trace impurities at 0.01 ng/g concentrations has been possible using SSMS isotope dilution on samples amenable to preconcentration techniques. Isotope dilution requires dissolution of samples before the... 

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