Atomic trace analysis

Atomic absorption using either flame or electrothermal atomization is widely used for the analysis of trace metals in a variety of sample matrices. Using the atomic absorption analysis for zinc as an example, procedures have been developed for its determination in samples as diverse as water and wastewater, air, blood, urine, muscle... 

The extreme sensitivity and high resolving power of trace analysis techniques encourage the quest for single atom detection. 

The potential usefulness of x-ray emission spectrography for trace analysis is implicit in the results of approximate calculations presented in Chapter 4. Thus, it was estimated that the intensity of cobalt Ka generated under practicable conditions in a monolayer (area, 1 sq cm) of cobalt atoms might give 133 counts per second (4.16). Such a sample weighs 0.2 pg. 

Aqueous standard solutions are a source of certain difficulties In electrothermal atomic absorption spectrometry of trace metals In biological fluids The viscosities and surface tensions of aqueous standard solutions are substantially less than the viscosities and surface tensions of serum, blood and other proteln-contalnlng fluids These factors Introduce volumetric disparities In pipetting of standard solutions and body fluids, and also cause differences In penetration of these liquids Into porous graphite tubes or rods Preliminary treatment of porous graphite with xylene may help to minimize the differences of liquid penetration (53,67) A more satisfactory solution of this problem Is preparation of standards In aqueous solutions of metal-free dextran (50-60 g/llter), as first proposed by Pekarek et al ( ) for the standardization of serum chromium analyses This practice has been used successfully by the present author for standardization of analyses of serum nickel The standard solutions which are prepared In aqueous dextran resemble serum In regard to viscosity and surface tension Introduction of dextran-contalnlng standard solutions Is an Important contribution to electrothermal atomic absorption analysis of trace metals In body fluids. 

Asplla, K. I., Chakrabartl, C. L., and Bratzel, M. P., Jr. "Pyrolytic Graphite-Tube Micro-Furnace for Trace Analysis by Atomic Absorption Spectrometry". Anal. Chem. (1972),... 

Analysis of Corexit 9527. Corexit 9527 in natural waters can be analyzed. The method is based on the formation of a Z>w(ethylenediamine) copper(II) complex, extraction of the complex into methylisobutylketone, and atomic absorption spectroscopy [1564]. The method is suitable for a concentration range of 2 to 100 mg/liter, with a precision as low as 5% relative to standard deviation for samples in the middle- to high range. Only a small sample volume (10 ml) is required. The sensitivity may be substantially increased for trace analysis by increasing the sample volume. 

HPLC-QFAAS is also problematical. Most development of atomic plasma emission in HPLC detection has been with the ICP and to some extent the DCP, in contrast with the dominance of the microwave-induced plasmas as element-selective GC detectors. An integrated GC-MIP system has been introduced commercially. Significant polymer/additive analysis applications are not abundant for GC and SFC hyphenations. Wider adoption of plasma spectral chromatographic detection for trace analysis and elemental speciation will depend on the introduction of standardised commercial instrumentation to permit interlaboratory comparison of data and the development of standard methods of analysis which can be widely used. 

The extension of inductively coupled plasma (ICP) atomic emission spectrometry to seawater analysis has been slow for two major reasons. The first is that the concentrations of almost all trace metals of interest are 1 xg/l or less, below detection limits attainable with conventional pneumatic nebulisation. The second is that the seawater matrix, with some 3.5% dissolved solids, is not compatible with most of the sample introduction systems used with ICP. Thus direct multielemental trace analysis of seawater by ICP-AES is impractical, at least with pneumatic nebulisation. In view of this, a number of alternative strategies can be considered ... 

The relative advantages and disadvantages ofvoltammetric and atomic absorption methodologies are listed below. It is concluded that for laboratories concerned with aquatic chemistry of metals (which includes seawater analysis), instrumentation for both AAS (including potentialities for graphite furnace AAS as well as hydride and cold vapour techniques) and voltammetry should be available. This offers a much better basis for a problem-orientated application of both methods, and provides the important potentiality to compare the data obtained by one method with that obtained in an independent manner by the other, an approach that is now common for the establishment of accuracy in high-quality trace analysis. 

Thermal ionization TI Ionization by heating Atomic ions Isotope ratio, Trace analysis Solid samples... 

Spark source SS Discharge Atomic ions Trace analysis in solid samples... 

Glow discharge GD Plasma source Atomic ions Trace analysis... 

Laser desorption/ ionization LDI Photon induced desorption/ ionization Nonvolatile atomic and molecular ions Isotope ratio Trace analysis... 

The voltammograms were calculated by assuming that no metal atoms were initially present in the film. The response depends on the dimensionless film thickness A = Z(//D) /, where L is the real film thickness [40]. Figure 2.23a shows that the dimensionless net response is the highest if A = 1. This condition is satisfied if, for instance, D = 9 x 10 cm /s, / = 100 Hz and L = 3 pm, which is rather thick film. In trace analysis the films are usually much thiimer than a micrometer [41]. The maximum net response appears if the film thickness is approximately equal to... 

A convenient method is the spectrometric determination of Li in aqueous solution by atomic absorption spectrometry (AAS), using an acetylene flame—the most common technique for this analyte. The instrument has an emission lamp containing Li, and one of the spectral lines of the emission spectrum is chosen, according to the concentration of the sample, as shown in Table 2. The solution is fed by a nebuhzer into the flame and the absorption caused by the Li atoms in the sample is recorded and converted to a concentration aided by a calibration standard. Possible interference can be expected from alkali metal atoms, for example, airborne trace impurities, that ionize in the flame. These effects are canceled by adding 2000 mg of K per hter of sample matrix. The method covers a wide range of concentrations, from trace analysis at about 20 xg L to brines at about 32 g L as summarized in Table 2. Organic samples have to be mineralized and the inorganic residue dissolved in water. The AAS method for determination of Li in biomedical applications has been reviewed . 

AFS (Atomic fluore- (i) Good for trace analysis. No instrumentation... 

For many elements, the atomization efficiency (the ratio of the number of atoms to the total number of analyte species, atoms, ions and molecules in the flame) is 1, but for others it is less than 1, even for the nitrous oxide-acetylene flame (for example, it is very low for the lanthanides). Even when atoms have been formed they may be lost by compound formation and ionization. The latter is a particular problem for elements on the left of the Periodic Table (e.g. Na Na + e the ion has a noble gas configuration, is difficult to excite and so is lost analytically). Ionization increases exponentially with increase in temperature, such that it must be considered a problem for the alkali, alkaline earth, and rare earth elements and also some others (e g. Al, Ga, In, Sc, Ti, Tl) in the nitrous oxide-acetylene flame. Thus, we observe some self-suppression of ionization at higher concentrations. For trace analysis, an ionization suppressor or buffer consisting of a large excess of an easily ionizable element (e g. caesium or potassium) is added. The excess caesium ionizes in the flame, suppressing ionization (e g. of sodium) by a simple, mass action effect ... 

Different analytical techniques such as ICP-OES (optical emission spectrometry with inductively coupled plasma source), XRF (X-ray fluorescence analysis), AAS (atomic absorption spectrometry) with graphite furnace and flame GF-AAS and FAAS, NAA (neutron activation analysis) and others, are employed for the trace analysis of environmental samples. The main features of selected atomic spectrometric techniques (ICP-MS, ICP-OES and AAS) are summarized in Table 9.20.1 The detection ranges and LODs of selected analytical techniques for trace analysis on environmental samples are summarized in Figure 9.15.1... 

When trace analysis is performed, well-established protocols have to be followed to obtain reliable results. The production of free atoms in the flame or furnace can be modified according to the composition of the matrix in which the sample is found. Therefore, salts and mineral or organic reagents are often introduced in the solutions to be nebulised. 

The isotopic dilution method can be extended to non-radioactive tracers by using mass spectrometry or NMR to determine the variation in isotopic ratios. This method can be used for the measurement of molecules or elemental species (about 60 elements have stable isotopes). This approach allows ultra-trace analysis because, contrary to radioactive labelling where the measurement relies on detecting atoms that decompose during the period of measurement, all labelled atoms are measured. Isotopic mass spectrometers are well suited for these measurements. 

Every coupling application favors one part of the coupling system. A dominating chromatography part leads to the speciation analysis [5,6,26,27]. The elemental specific detection facilities of atomic spectrometry are strongly favored over the multielement capabilities. An inversion of this construction leads to multielement trace analysis in complex matrices with the use of chromatographic equipment as powerful preconcentration and matrix elimination tool [13k The ability of chromatography for a further time resolution between the separated traces is not really required because of the excellent elemental specific detection capabilities of atomic spectrometry. 

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