Atomic absorption spectroscopy AAS

The quantitative determination of a metal can be carried out using atomic absorption spectroscopy (AAS) by observing the diagnostic absorption spectrum of gaseous atoms of the metal. 

The emission spectmm of atomic hydrogen (Section 1.4) consists of a series of sharp lines, each line corresponding to a discrete electronic transition fi om higher to lower energy levels (Fig. 1.3). Conversely, if atomic hydrogen is irradiated, it will give rise to an absorption spectrum. Every element has a characteristic atomic emission and absorption spectrum, and the most common analytical method for quantitative determination of a given metal is atomic absorption spectroscopy (AAS). Usually, radiation 

The cation, drawn below was prepared as the salt [X][PF6]2. Elemental analysis showed the compound to be [XKPFsli J NalPFg]. The complex is soluble in 

A stock solntion (1.0 x 10 moldm ) of NaCl was prepared. Standards were made by adding 2.0, 3.0, 4.0, 6.0 or 10.0 cm of the stock solution to a 100 cm volumetric flask 5cm of MeCN were added to each flask which was then filled to the 100 cm mark with deionized water. A blank was also prepared. The sample for analysis was prepared by dissolving 8.90 mg of [X][PF6l2 xNalPFgl in 2.5 cm of MeCN in a 50 cm volumetric flask. This was filled to the mark with deionized water. This solution was diluted 10-fold with a 5% (by volume) MeCN/water solution. Using a sodinm hollow cathode lamp (A = 589nm), AAS was nsed to determine the absorbance of each standard. Each absorbance reading was corrected for the absorbance of the blank and the data are tabulated below  

X can be determined by finding the ratio of the number of moles of [X][PF6l2 Na[PFg]. 

Atomic absorption completely replaced OES in archaeological chemistry during the 1980s, and differs from it in a number of ways. Firstly, it is primarily a solution-based technique, therefore requiring solid samples to be dissolved prior to analysis. Secondly, it is based on the absorption of light by atomized samples in a flame, in contrast to OES which is based on emission. Because of this, AAS requires a source of light that has a wavelength 

The heart of a traditional atomic absorption spectrometer is the burner, of which the most usual type is called a laminar flow burner. The stability of the flame is the most important factor in AAS. Typical working temperatures are 2200 2400°C for an air-acetylene flame, up to 2600-2800°C for acetylene-nitrous oxide. The fraction of species of a particular element that exist in the excited state can be calculated at these temperatures using the Boltzmann equation  

The design of a conventional atomic absorption spectrometer is relatively simple (Fig. 3.1), consisting of a lamp, a beam chopper, a burner, a grating monochromator, and a photomultiplier detector. The design of each of these is briefly considered. The figure shows both single and double beam operation, as explained below. 

The light passing through the flame must be of exactly the same frequency as the absorption line, in order to stimulate the analyte atoms in the flame to absorb. Because of the narrow absorption lines of the atomic plasma in the 

As with all other types of spectrometers operating in the UV/visible region of the spectrum, it is advantageous to modulate the primary beam using a mechanical beam chopper, and detect it at the same frequency, to reduce background noise. This is usually done with a rotating beam chopper, shaped 

This technique, and the related inductively coupled plasma (ICP), are used where it is necessary to quantify metals in a plastic compound. Although not often required it can be of use in the analysis of flame retardant systems, where additives such as antimony trioxide and zinc borate have been used. 

This technique is very useful for obtaining semi-quantitative elemental data from plastic compoimds and their ashes. Among other things, it helps to identify inorganic fillers and pigments in samples. The technique is usually used in conjunction with IR. 

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Atomic absorption spectroscopy (AAS) is complementary to atomic emission spectroscopy (see Section 3.5.3) and became available for a wide range of atoms in the mid-1950s. 

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

Pretreatment of the collected particulate matter may be required for chemical analysis. Pretreatment generally involves extraction of the particulate matter into a liquid. The solution may be further treated to transform the material into a form suitable for analysis. Trace metals may be determined by atomic absorption spectroscopy (AA), emission spectroscopy, polarogra-phy, and anodic stripping voltammetry. Analysis of anions is possible by colorimetric techniques and ion chromatography. Sulfate (S04 ), sulfite (SO-, ), nitrate (NO3 ), chloride Cl ), and fluoride (F ) may be determined by ion chromatography (15). 

Discussion. Because of the specific nature of atomic absorption spectroscopy (AAS) as a measuring technique, non-selective reagents such as ammonium pyrollidine dithiocarbamate (APDC) may be used for the liquid-liquid extraction of metal ions. Complexes formed with APDC are soluble in a number of ketones such as methyl isobutyl ketone which is a recommended solvent for use in atomic absorption and allows a concentration factor of ten times. The experiment described illustrates the use of APDC as a general extracting reagent for heavy metal ions. 

Iron was present as Fe " in the calcined precursors. For all the catalysts the reduction procedure described in Sec. 2.1 resulted in incomplete reduction of the Fe to metallic iron. This is in agreement with the findings of previous authors [6,11]. The individual percentage reductions of Fe to Fe°, as determined by the separate gravimetric and volumetric measurements (Sec. 2.2), are shown in Table 1. The values are calculated on the assumption that all the Fe is reduced to Fe prior to the onset of reduction to Fe°. There is good agreement between the two methods. Table 1 also records the actual Fe/(Fe + Mg) ratio in the catalysts as determined by atomic absorption spectroscopy (AAS) on the calcined precursors. 

The total metal concentration in a solution can be easily determined using methods such as atomic absorption spectroscopy (AAS) however, the bioavailability of different metal species likely varies. In addition, much of the original concentration may have speciated into insoluble precipitates. Therefore, the concentration of some bioavailable species may be extremely low, perhaps even within or below the nanomolar range.99 Ion-selective electrodes are useful for measuring the bioavailable concentration of a metal because they measure only the free, ionic species, which is often most prevalent.102... 

Atomic absorption spectroscopy (AAS) Differential scanning calorimetry (DSC)... 

Of particular concern in this analysis is sodium because it destroys soil structure, is associated with increased soil pH, and can be toxic to plants. Sodium can easily be determined by atomic absorption spectroscopy (AAS), flame ionization spectroscopy (FIS), and inductively coupled plasma (ICP) methods. Soil structure is discussed in Chapter 2 and the various spectroscopic methods discussed in Chapter 14. 

Air-dry soil is mixed with 0.02 M calcium chloride solution (1 2 ratio, for instance, 10-g soil 20 mL 0.02 M CaCl2 solution) and mixed for 1 hour. The pH of the suspension can be measured directly. In addition, the solution can be filtered for the determination of aluminum or magnesium by atomic absorption spectroscopy (AAS) or inductively coupled plasma (ICP) spectroscopy (adapted from Reference 5). 

Step-VI The absorption of radiant energy by some atoms into their higher energy levels enable them to radiate energy (atomic absorption) measured by Atomic Absorption Spectroscopy (AAS). 

Allan Walsh, in 1955, was the pioneer for the introduction of atomic absorption spectroscopy (AAS), which eventually proved to be one of the best-known-instrumental-techniques in the analytical armamentarium, that has since been exploited both intensively and extensively in carrying out the quantitative determination of trace metals in liquids of completely diversified nature, for instance blood serum-for Ca2+, Mg2+, Na+ and K+ edible oils-Ni2+ beer samples-Cu+ gasoline (petrol)-Pb2+ urine-Se4+ tap-water-Mg2+ Ca2+ lubricating oil-Vanadium (V). 

The underlying principle of atomic absorption spectroscopy (AAS) is the absorption of energy exclusively by ground state atoms while they are in the gaseous form. 

In atomic absorption spectroscopy (AAS) the technique using calibration curves and the standard addition method are both equally suitable for the quantitative determinations of elements. 

Both atomic emission spectroscopy (AES) and atomic absorption spectroscopy (AAS) are used to identify and quantify the elements present in a sample. 

Membrane morphology is studied with scanning electron microscopy (SEM) thereby providing an Insight into the relationship between asymmetric membrane preparation, structure, and performance (29,3A). The extent of ion exchange of the salt form of the SPSF membranes is studied with atomic absorption spectroscopy (AAS), neutron activation analysis (NAA), and ESCA. AAS is used for solution analysis, NAA for the bulk membrane analysis, and ESCA for the surface analysis. 

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