Single-element analysis

Apart from multi-element analysis employed for large scale studies, single element analysis (e.g., especially of toxic elements such as Cd, Hg, Tl or Pb) is performed in environmental science for special applications. For example, Hg and Tl have been determined in environmental samples by slurry sampling using electrothermal vaporization (ETV) ICP-MS. If potassium permanganate is employed as a modifier in ETV at optimized pyrolysis temperatures of 300 °C for Hg and 500 °C for Tl, detection limits of 0.18p,gg 1 (Hg) and 0.07p,gg 1 (Tl) are obtained.58... 

The time spent on atomic absorption analysis depends essentially on the time required for a solution of the sample to be produced this is generally much greater than the time required for the preparation of references and for measurements. This is a single element analysis technique. A range of references for the element to be determined is prepared for each series of samples. 

The potential of ultrasonic extraction for field-based extractions has been put into use in the industrial hygiene and environmental single-element analysis of, for example, lead from glass fibre filter ambient air samples [13,14] or from lead-based paint, urban dust and river sediment [15] hexavalent chromium from coal fly ash and paint chips [16] and strontium from river sediment [17]. Ultrasonic extraction has also proved effective as a prior step in multi-element determinations of heavy metals. 

The analytical techniques used for single element analysis can be divided into three groups. The first group consists of titration techniques using various means to detect the end point of titration, such as volumetric titration, fluorophotometric titration, potentiometric titration, and spectrophotometric titration. The second group includes direct detection techniques such as direct ternary inclusion compound fluorescent spectrophotometry and the use of ISEs. The third group is that of separation methods such as IC and HPLC, which are used in complicated sample matrices to reduce the sample matrix interference. 

Procedures based on separation techniques such as HPLC and IC have been developed for single element analysis for the following two reasons. The first reason is to remove interferents in complicated sample matrices that can give rise to incorrect results, in particular for trace analysis in samples with a high organic content, such as the determination of total iodine in egg products. The second reason is to differentiate the total and free forms of a specific element, such as the determination of the free iodide ion and bounded iodine in food additives. The free iodide ion is determined by direct sample injection into the IC column, whereas the total iodine content is determined after oxygen flask combustion. Thus, both the free and bounded forms of iodine in food samples can be determined. 

In the early 1970s, Simonits proposed the development of a standardization method using universal fc-factors. In this method, the essential information for a gamma ray emitted by any nuclide produced by neutron activation would be contained in a universal constant, the ko factor, and all factors depending on the specific irradiation and counting conditions would be calculated by models. The inventors of the ko method envisioned that for each sample analyzed at least one neutron flux monitor would be co-irradiated and counted, and all other parameters of the models would be measured once and only remeasmed when irradiation conditions changed. Thus, multielement analysis could be performed with the same amount of work needed for single-element analysis. 

Atomic absorption spectroscopy is more suited to samples where the number of metals is small, because it is essentially a single-element technique. The conventional air—acetylene flame is used for most metals however, elements that form refractory compounds, eg, Al, Si, V, etc, require the hotter nitrous oxide—acetylene flame. The use of a graphite furnace provides detection limits much lower than either of the flames. A cold-vapor-generation technique combined with atomic absorption is considered the most suitable method for mercury analysis (34). 

MATHEMATICAL BASIS AND SOFTWARE FOR SINGLE GRAIN MILLIPROBE XRF TRACE ELEMENT ANALYSIS (XRF-MP/SG) OF ACCESSORY MINERALS... 

Ever brighter vacuum-ultraviolet sources are being developed that would further boost SPI sensitivity, which already is typically 10 useful yield general, sensitive elemental analysis would then also be available using SPI, making possible a single laser arrangement for both elemental and molecular SALE... 

In addition to qualitative analysis of nearly all the elements of the periodic table, EEL spectra also enable determination of the concentration of a single element which is part of the transmitted volume and hence gives rise to a corresponding ionization edge. As in all comparable spectroscopic techniques, for quantification the net edge signal, which is related to the number N of excited atoms, must be extracted from the raw data measured. The net intensity 4 of the feth ionization shell of an individual element is directly connected to this number, N, multiplied by the partial cross-section of ionization ) and the intensity Iq of the incident electron beam, i.e. ... 

The advantages of LA are now well-known - no sample preparation is needed, conducting and non-conducting samples of arbitrary structure can be analyzed directly, spatial resolution up to a few microns can be obtained, high vacuum conditions are not required, rapid simultaneous multi-element analysis is possible, and it is possible to obtain complete analytical information with a single laser pulse. A brief overview of the potential and limitations of LA will be given in this chapter. 

Most commercial polymers are substantially linear. They have a single chain of mers that forms the backbone of the molecule. Side-chains can occur and can have a major affect on physical properties. An elemental analysis of any polyolefin, (e.g., polyethylene, polypropylene, poly(l-butene), etc.) gives the same empirical formula, CH2, and it is only the nature of the side-chains that distinguishes between the polyolefins. Polypropylene has methyl side-chains on every other carbon atom along the backbone. Side-chains at random locations are called branches. Branching and other polymer structures can be deduced using analytical techniques such as NMR. 

These observations indicated that an intermolecular double condensation to give a bis N-(methylene-4-oxocoumarinyl)-l,4 aromatic diamine had occurred. Data from the elemental analysis indicated that the calculated and observed values were within the acceptable limits ( 0.4%) and in conformity with the assigned structure. In the addition of molar equivalents of 1,4-aromatic binucleophilic compounds to compound 72 we did not observe any heterocyclic compounds resulting from the further intermolecular nucleophilic attack on the single condensation product. Since the condensation of 3-(dimethylaminomethylene)-chromane-2,4-dione with aromatic binucleophilic compounds is the only route to the new coumarinic compounds, this represents a useful synthetic method. 

As XRF is not an absolute but a comparative method, sensitivity factors are needed, which differ for each spectrometer geometry. For quantification, matrix-matched standards or matrix-correction calculations are necessary. Quantitative XRF makes ample use of calibration standards (now available with the calibrating power of some 200 international reference materials). Table 8.41 shows the quantitative procedures commonly employed in XRF analysis. Quantitation is more difficult for the determination of a single element in an unknown than in a known matrix, and is most complex for all elements in an unknown matrix. In the latter case, full qualitative analysis is required before any attempt is made to quantitate the matrix elements. 

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