Total Element Content Determination

The determination of species concentrations tends to be more challenging than determination of total element contents because... 

The unique aspects of speciation procedures arise from the additional specification that the procedure adopted should not disturb existing equilibrium conditions. The choice of procedure is further restricted by the fact that the total concentration of element present in a sample (e.g. Cu, Pb, Cd, Zn in water samples) is often near the detection limits of many standard analytical techniques, and modified or refined techniques are required to handle the even lower levels present in isolated sub-categories. In biological matrices, the concentrations of inorganic and organo-metallic compounds present can range from 10 3 to 10 12 mol dm 3, and at the lower levels even the determination of total element content can be greatly in error, if suitable correction is not made for interference effects which can arise from the nature of the sample. 

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... 

Table 2.8 Determination of the labile fraction of total element content...

Up to 30 elements can be determined by voltammetric procedures, but when the metals of interest are present at 10-9 to 10 12 mol dm-3 levels, the introduction of a pre-concentration step becomes essential. The concentration process may disturb the distribution pattern of labile molecular species but the status of stable species should change little. Some pre-concentration procedures can be selective in respect to the species retained, and this can limit the value of total element content analyses (i.e. procedures need to be validated). 

For environmental, biological, or health-related investigations, the primary limitation of ICAP analysis is related to the totality of the analysis. The concentrations of specific element forms are often more important than total element content in these disciplines. ICAP analysis by direct pneumatic nebulization to date must be considered to provide only the total content of each element analyzed, independent of the forms. If a specific element form is to be determined, appropriate separation techniques must be used prior to analysis by conventional sample introduction to an ICAP. 

The eco-toxicity and mobility of metals in the environment depends strongly on their specific chemical forms or types of binding rather than the total element contents. Consequently these have to be determined in order to assess the toxic effects and geochemical pathways. The determination of specific chemical species or binding forms is difficult and often hardly possible. Therefore, in practice determinations of broader operationally or functionally defined forms or phases can be a reasonable compromise ... 

ISO 14869-1 2001 Soil quality - Dissolution for the determination of total element content - Part 1 Dissolution with hydrofluoric and perchloric acids. 

This chapter includes sections on The Analytical Method, Sampling and Sample Treatment, Separation and Concentration, Method Classification, and Determinative Methods. The principal thrust of this chapter is a general summary of some of the more common and current analytical methodologies employed for the determination of total elemental contents in a wide variety of biological and environmental materials. Coverage here is general the reader is referred to other chapters in this book for particular details on individual elements covered there and to the many publications referred in this chapter. The chapter... 

Stomach acid extraction, with metal concentrations reported on a dry weight basis. Total elemental contents in the dust sample were determined using strong acid digestion followed by induetively coupled plasma mass spectrometry (ICP-MS), as follows Ca 8.95 wt% Fe 0.79 wt% A1 1.16 wt% Mn 156 mg kg Ni 45.5 mg kg Cu 260 mg kg Zn 1,220 mg kg and Pb 1,670 mg kg . The bioaceessible eontent of Pb as determined by simulated stomach acid digestion was 1,586 mg kg . Bulk powdered XRD analysis identified the presence of calcite and various alumino-silicates. 

With regard to chemical reactions, target aquifer samples have been determined to give information on grain size distribution and porosity, and quantitative chemical analysis for total element content (by X-ray fluorescence (XRF)), iron sulfides, calcium carbonate, exchangeable cations, organic matter, and organic carbon. 

For an efficient dissolution of the ash of samples with silicate compounds in the matrix, such problems highlight the absolute necessity of utilizing an HF step followed by evaporation to dryness if the objective is the determination of total element content. However, this problem, typically associated with plant samples, is similar when applying a wet digestion procedure if an insoluble residue remains, an additional HF step, followed by evaporation to dryness, must also be performed. 

Since ICP-MS detection is used, a nonanalyte element may be spiked into the eluent to provide a known, urtiform signal for instrument optimization. Alternatively, the column may be removed from the sample introduction apparatus to allow direct pumping of optimization solutions to the detector. Another advantage of removing the column is that the total element content of a particular species can be determined and compared to the total amount of the various species. This could be done automatically with a six-port, two-position switching valve where... 

The total cerium content in the single crystal samples on the basis of rare-earth elements is determined by photometry after Ce(III) oxidation by ammonium persulfate. The Ce(III) content is calculated from the difference. Comparison of the determination results of the total cerium content obtained by photometric and atomic emission methods for Li GdlBO ljiCe demonstrated the elaborated procedure precision and systematic error absence. 

Matrix Components The term matrix component refers to the constituents in the material aside from those being determined, which are denoted as analyte. Clearly, what is a matrix component to one analyst may be an analyte to another. Thus, in one hand for the case of analyses for elemental content, components such as dietary fibre, ash, protein, fat, and carbohydrate are classified as matrix components and are used to define the nature of the material. On the other hand, reference values are required to monitor the quality of determinations of these nutritionally significant matrix components. Hence, there is a challenging immediate need for certified values for dietary fibre, ash, protein, fat, and carbohydrate. Concomitantly, these values must be accompanied by scientifically sound definitions (e.g. total soluble dietary fibre, total sulpha-ted ash, total unsaturated fat, polyunsaturated fat, individual lipids, simple sugars, and complex carbohydrates). 

Principles and Characteristics The fastest growing area in elemental analysis is in the use of hyphenated techniques for speciation measurement. Elemental spe-ciation analysis, defined as the qualitative identification and quantitative determination of the individual chemical forms that comprise the total concentration of an element in a sample, has become an important field of research in analytical chemistry. Speciation or the process yielding evidence of the molecular form of an analyte, has relevance in the fields of food, the environment, and occupational health analysis, and involves analytical chemists as well as legislators. The environmental and toxicological effects of a metal often depend on its forms. The determination of the total metal content... 

Determination of the level of total sulfur in a rubber can give information on the type of cure system used, for example, elemental sulfur plus accelerator or sulfur donor system, etc. The ISO 6528-1 1992 method — Rubber — Determination of total sulfur content — Part 1 Oxygen combustion flask method is often employed. The principle of the method is oxidation by ignition in an atmosphere of oxygen in the presence of hydrogen peroxide, conversion of sulfur to sulfuric acid and determination of the sulfate by titration with barium perchlorate. The method is... 

Recently, methods for quantitatively determining the chemical element composition of solid materials by x-ray emission spectroscopy using the electron microprobe have become available. A significant advantage of the electron microprobe, compared with methods for bulk analysis. Is Its capability for rapid analysis of many different mlcron-slze areas of a solid sample. Thus, In a relatively short time, we can obtain several hundred quantitative analyses of the chemical element content of a solid sample. These analyses usually will be different because sample homogeneity Is absent on the micron level. Thus, each chemical analysis Is a linear sum of the chemical elements In the subset of minerals present at that location. Generally, we expect the number of minerals present In a mlcron-slze spot to be less than the total number of minerals In the bulk sample. 

The second reason for acid-digestion is the determination of the total soil elemental content of, e.g. potassium, phosphorus or trace elements. This is seldom done for potassium in normal soil samples, mainly because the total K in soils is of no value as an index to the availability of K to plants, nor is it always of value in tracing the movement or accumulation of applied fertilizer K (Pratt, 1965). The unreactive soil phosphorus is obtained by subtracting the naturally leached reactive phosphorus from the total phosphorus, and a method for determining the latter by extraction with sulphuric acid and potassium persulphate is cited by Turner and FHaygarth (2000). They analysed... 

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