Quantitation atomic absorption spectrometry

In this work, a method based on the reduction potential of ascorbic acid was developed for the sensitive detennination of trace of this compound. In this method ascorbic acid was added on the Cr(VI) solution to reduced that to Cr(III). Cr(III) produced in solution was quantitatively separated from the remainder of Cr(VI). The conditions were optimized for efficient extraction of Cr(III). The extracted Cr(III) was finally mineralized with nitric acid and sensitively analyzed by electro-thermal atomic absorption spectrometry. The determinations were carried out on a Varian AA-220 atomic absolution equipped with a GTA-110 graphite atomizer. The results obtained by this method were compared with those obtained by the other reported methods and it was cleared that the proposed method is more precise and able to determine the trace of ascorbic acid. Table shows the results obtained from the determination of ascorbic acid in two real samples by the proposed method and the spectrometric method based on reduction of Fe(III). 

Mercury vapour in air Diffusive samplers with qualitative onsite colorimetric analysis and quantitative cold vapour atomic absorption spectrometry in the laboratory 59... 

Bruland et al. [122] have shown that seawater samples collected by a variety of clean sampling techniques yielded consistent results for copper, cadmium, zinc, and nickel, which implies that representative uncontaminated samples were obtained. A dithiocarbamate extraction method coupled with atomic absorption spectrometry and flameless graphite furnace electrothermal atomisation is described which is essentially 100% quantitative for each of the four metals studied, has lower blanks and detection Emits, and yields better precision than previously published techniques. A more precise and accurate determination of these metals in seawater at their natural ng/1 concentration levels is therefore possible. Samples analysed by this procedure and by concentration on Chelex 100 showed similar results for cadmium and zinc. Both copper and nickel appeared to be inefficiently removed from seawater by Chelex 100. Comparison of the organic extraction results with other pertinent investigations showed excellent agreement. 

One of the advantages of the isotope dilution technique is that the quantitative recovery of the analytes is not required. Since it is only their isotope ratios that are being measured, it is necessary only to recover sufficient analyte to make an adequate measurement. Therefore, when this technique is used in conjunction with graphite furnace atomic absorption spectrometry, it is possible to determine the efficiency of the preconcentration step. This is particularly important in the analysis of seawater, where the recovery is very difficult to determine by other techniques, since the concentration of the unrecovered analyte is so low. In using this technique, one must assume that isotopic equilibrium has been achieved with the analyte, regardless of the species in which it may exist. 

Only arc/spark, plasma emission, plasma mass spectrometry and X-ray emission spectrometry are suitable techniques for qualitative analysis as in each case the relevant spectral ranges can be scanned and studied simply and quickly. Quantitative methods based on the emission of electromagnetic radiation rely on the direct proportionality between emitted intensity and the concentration of the analyte. The exact nature of the relation is complex and varies with the technique it will be discussed more fully in the appropriate sections. Quantitative measurements by atomic absorption spectrometry depend upon a relation which closely resembles the Beer-Lambert law relating to molecular absorption in solution (p. 357 etal.). 

Procaine was indirectly determined by Minami et al. using atomic absorption spectrometry [51]. Nerin et al. also used indirect atomic spectrometiy to determine procaine, with their method involving the formation of an ion-pair with Co(SCN)4 and extraction of the ion pair into 1,2-dichloroethane [52. Quantitation of the Co response was effected using the atomic absorption at 241 nm, and optimal pH conditions and the linear regions of the calibration graphs were reported. 

Atomic Absorption Spectrometry. Principles of Quantitative Analysis... 

This method is based on the emission of light by atoms returning from an electronically excited to the ground state. As in atomic absorption spectrometry, the technique involves introduction of the sample into a hot flame, where at least part of the molecules or atoms are thermally stimulated. The radiation emitted when the excited species returns to the ground state is passed through a monochromator. The emission lines characteristic of the element to be determined can be isolated and their intensities quantitatively correlated with the concentration of the solution. 

Carbon Monoxide. Methods for determining carbon monoxide include detection by conversion to mercury vapor, gas filter correlation spectrometry, TDLAS, and grab sampling followed by gas chromatograph (GC) analysis. The quantitative liberation of mercury vapor from mercury oxide by CO has been used to measure CO (73). The mercury vapor concentration is then measured by flameless atomic absorption spectrometry. A detection limit of 0.1 ppbv was reported for a 30-s response time. Accuracy was reported to be 3% at tropospheric mixing ratios. A commercial instrument providing similar performance is available. 

In the test method, the coal or coke to be analyzed is ashed under controlled conditions, digested by a mixture of aqua regia and hydrofluoric acid, and finally dissolved in 1% nitric acid. The concentration of individual trace elements is determined by either inductively coupled plasma-atomic emission spectrometry (ICPAES) or inductively coupled plasma-mass spectrometry (ICPMS). Selected elements that occur at concentrations below the detection limits of ICPAES can be analyzed quantitatively by graphite furnace atomic absorption spectrometry (GFAA). 

H. J. Salacinski, P. G. Riby, S. J. Haswell, Coupled flow-injection analysis-flame atomic absorption spectrometry for the quantitative determination of aluminum in beverages and waters incorporating on-line cation exchange, Anal. Chim. Acta, 269 (1992), 1-7. 

Munoz, D. Velez, M. L. Cervera, R. Montoro, Rapid and quantitative release, separation and determination of inorganic arsenic (As(III) + As(V)) in seafood products by microwave-assisted distillation and hydride generation atomic absorption spectrometry, J. Anal. Atom. Spectrom., 14 (1999), 1607-1613. 

Fitchett, A.W., Daughtrey, E.H., Mushak, J.P. Quantitative measurements of inorganic and organic arsenic by flameless atomic absorption spectrometry. Anal. Chim. Acta 79, 93-99 (1975)... 

A procedure was developed for the determination of total and labile Cu and Fe in river surface water. It involved simultaneous solvent extraction of the metals as diethyldithio-carbamates (ddc) and tfac complexes. The complexes were extracted by isobutyl methyl ketone (ibmk) and the solution subjected to flame atomic absorption spectrometry. Variables such as pH, metal complex concentration, reaction time, ibmk volume and extraction time were optimized. Prior to the solvent extraction a microwave-assisted peroxydisulfate oxidation was used to break down the metallorganic matter complexes in the river surface waters . Trifluoroacetylacetone was used as a chelation agent for the extraction and quantitative determination of total Cr in sea water. The chelation reaction was conducted in a single aqueous phase medium. Both headspace and liquid phase extractions were studied and various detection techniques, such as capillary GC-ECD, EI-MS (electron-impact MS) and ICP-MS, were tested and compared. The LOD was 11-15 ngL Cr for all the systems examined. The method provided accurate results with EI-MS and ICP-MS, while significant bias was experienced with ECD °. ... 

The application of atomic absorption spectrometry to quantitative analysis is illustrated in Figure 2.2. The incident radiation at resonance wavelength with intensity /q is focused on the flame containing the atoms in their fundamental state and is transmitted with a reduced intensity I determined by the concentration of the atoms in the flame. The radiation is directed to the detector where the intensity is measured. The quantity of absorbed light is determined by comparing / to /q. 

A second extended function of the liquid column chromatography is to preseparate trace amounts of several substances for subsequent quantitative analysis by a selective determination method such as atomic absorption spectrometry (Table 2.3). Here often only a particular degree of separation is achieved. Non separated elements are to be determined with high-selective methods. In most cases an enrichment is combined with these chromatographic methods (Chap. 4). 

The use of furnaces as atomizers for quantitative AAS goes back to the work of L vov and led to the breakthrough of atomic absorption spectrometry towards very low absolute detection limits. In electrothermal AAS graphite or metallic tube or cup furnaces are used, and through resistive heating temperatures are achieved at which samples can be completely atomized. For volatile elements this can be accomplished at temperatures of 1000 K whereas for more refractory elements the temperatures should be up to 3000 K. 

Atomic Absorption Spectrometry (AAS) is a quantitative spectroscopic method based on the ability of free atoms, produced in an appropriate medium, like a flame, plasma, or a heated graphite tube, to absorb radiation of an atom-specific wavelengfh. 

The special criteria of validation for an analytical method are directly related to the characteristics of the analytical method. For UV/Vis spectrometry, the reaction between the analyte and reagent must be fast, reproducible, and quantitative. The solution of the product resulting from the reaction must have at least 10,000 times the value of molar absorbtivity. In this regard, higher values can be obtained by using a polyfunctional reagent (e.g., Arsenazo III). For atomic absorption spectrometry and ICP, reproducibility of the flame and plasma, respectively, are essential for the quality and reliability of the analytical information, as well as for the validation criteria of the method. 

The range of off-line instruments available for water analysis Is wide. In fact, any analyser with optical or electrochemical detection can be adapted for this purpose. The use of liquid chromatography for the detection and quantitation of detergents or non-volatile organic compounds, of atomic absorption spectrometry for the analysis for heavy metal traces and of UV spectrophotometry for the determination of phosphates, nitrates and nitrites are representative examples of the potential utilization of conventional analysers for water analysis. 

Methods for quantitative analysis of Co indude flame and graphite-furnace atomic absorption spectrometry (AAS e.g., Welz and Sperling 1999), inductively coupled plasma emission spectrometry (ICP-AES e.g., Schramel 1994), neutron activation analysis (NAA e.g., Versieck etal. 1978), ion chromatography (e.g., Haerdi 1989), and electrochemical methods such as adsorption differential pulse voltammetry (ADPV e.g., Ostapczuk etal. 1983, Wang 1994). Older photometric methods are described in the literature (e.g.. Burger 1973). For a comparative study of the most commonly employed methods in the analysis of biological materials, see Miller-Ihli and Wolf (1986) and Angerer and Schaller... 

Tab. 2.4 Techniques for Quantitative Elemental Determination Atomic Absorption Spectrometry (AAS)...

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