Atomic absorption spectroscopy curves

Quantitative analysis in flame atomic absorption spectroscopy utilizes Beer s law. The standard curve is a Beer s law plot, a plot of absorbance vs. concentration. The usual procedure, as with other quantitative instrumental methods, is to prepare a series of standard solutions over a concentration range suitable for the samples being analyzed, i.e., such that the expected sample concentrations are within the range established by the standards. The standards and the samples are then aspirated into the flame and the absorbances read from the instrument The Beer s law plot will reveal the useful linear range and the concentrations of the sample solutions. In addition, information on useful linear ranges is often available for individual elements and instrument conditions from manufacturers and other literature. 

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. 

Belal et al [40] reported on the use of flame atomic absorption spectroscopy (FAAS), coupled with ion-exchange, to determine EDTA in dosage forms. EDTA is complexed with either Ca(II) or Mg(II) at pH 10, and the excess cations retained on an ion-exchange resin. At the same time, the Ca(II) or Mg(III) EDTA complexes are eluted and determined by AAS. Calibration curves were found to be linear over the range of 4-160 and 2-32 pg/mL EDTA when using Ca(II) or Mg(II), respectively. The method could be applied to eye drops and ampoules containing pharmaceuticals. Another combined AAS flow injection system was proposed for the determination of EDTA based on its reaction with Cu(II). The calibration curve was linear over the range of 5-50 pg/mL, with a limit of detection of 0.1 pg/mL [41]. 

In a linear dilution series the concentrations are separated by an equal amount, e.g. a series containing cadmium at 0, 0.2, 0.4, 0.6, 0.8, l.OmmolL" might be used to prepare a calibration curve for atomic absorption spectroscopy (p. 170) when assaying polluted soil samples. Use [Ci]F] =[C2]f2 to calculate the volume of standard solution for each member of the series and pipette or syringe the calculated volume into an appropriately sized volumetric flask as described above. Remember to label clearly each diluted solution as you prepare it, since it is easy to get confused. The process is outlined in Box 4.3. 

It has been found, however, in practice that a perfectly straight analytical working curve (— log T plotted against concentration) is seldom obtained in atomic absorption spectroscopy. The reasons for this are usually a combination of instrumental problems broadening of the emission line of the light source due to self-reversal, Doppler and pressure broadening of the absorption lines of the atoms in the flame, failure to exclude flame emission entirely, use of a focused instead of a parallel... 

The metal to protein stoichiometry was determined by atomic absorption spectroscopy using an Instrumentation Laboratory IL157 spectrometer. The concentration of metal ions in the RAGl proteins was measured in solutions of 3 to 10 pM protein. These were compared to either a Zn or Cd calibration curve ranging from 1 to 15 pM, which was measured prior to each protein sample. 

Flameless atomic absorption spectroscopy using the heated graphite furnace is a sensitive method for analyzing environ-mental samples for trace metals. High salt concentrations cause interference problems that are not totally correctable by optimizing furnace conditions and/or using background correctors. We determined that samples with identical ratios of major cations have trace metal absorbances directly related to their Na and trace metal concentrations. Equations and curves based on the Na concentration, similar to standard addition curves, can be calculated to overcome the trace element interference problem. Concentrations of Pb, Cd, Cu, and Fe in sea water can be simply (ind accurately determined from the Na concentration, the sample absorbance vs. a pure standard, and the appropriate curve. 

The characterisation of the colloids both in the free and in the embedded state was first performed using transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and atomic absorption spectroscopy (AAS). In addition, nitrogen adsorption-desorption curves at 77 K, H2-chemisorption measurements, solid state Si-NMR, XRD, SAXS, XPS, MAS-NMR, NH3-FTIR, and Au Mossbauer spectroscopy were applied. For the embedded triflates, the catalysts were characterized by nitrogen adsorption-desorption isotherms at 77K, TG-DTA, H, C, and Si solid state MAS-NMR, XRD, TEM, SEM, XPS and, FTIR after adsorption of NH3. 

Lithium metabolism and transport cannot be studied directly, because the lack of useful radioisotopes has limited the metabolic information available. Lithium has five isotopes, three of which have extremely short half lives (0.8,0.2, 10 s). Lithium occurs naturally as a mixture of the two stable isotopes Li (95.58%) and Li (7.42%), which may be determined using Atomic Absorption Spectroscopy, Nuclear Magnetic Resonance Spectroscopy, or Neutron Activation analysis. Under normal circumstances it is impossible to identify isotopes by using AAS, because the spectral resolution of the spectrometer is inadequate. We have previously reported the use of ISAAS in the determination of lithium pharmacokinetics. Briefly, the shift in the spectrum from Li to Li is 0.015 nm which is identical to the separation of the two lines of the spectrum. Thus, the spectrum of natural lithium is a triplet. By measuring the light absorbed from hollow cathode lamps of each lithium isotope, a series of calibration curves is constructed, and the proportion of each isotope in the sample is determined by solution of the appropriate exponential equation. By using a dual-channel atomic absorption spectrometer, the two isotopes may be determined simultaneously. - ... 

Why will a nonlinear calibration curve and a loss in sensitivity generally occur in atomic-absorption spectroscopy when using a continuum light-source as compared to a sharp-line source ... 

Metal-ion uptake in a dynamic system Sorption experiments in a dynamic system were carried out using a glass column (length 10 cm, internal diameter 1.2 cm) filled with 1.0 g resin. The resin was washed with distilled-deionized water (10 bed volumes), then a solution containing 40 ppm Cu was passed through at a flow rate of 3 mLmin . For determination of the breakthrough curve, the eluate from the column was collected in 50 mL fractions and the copper cation concentration was determined by atomic absorption spectroscopy. 

FIGURE 9-12. Flame emission calibration curves for magnesium (2852A) (A) 0-10, (B) 0-50, (C) 0-100 /.ig/vn. [From W. G. Schrenk, in Flame Emission and Atomic Absorption Spectroscopy, Vol. 2, Edited by J. A. Dean and T. C. Rains, Marcel Dekker, New York, (1971), Chapter 12. 

The potential/time profile for anodic stripping voltammetry and a typical experimental curve for the determination of a mixture of heavy metal ions is shown in Fig. 11.14. The method is clearly limited to the determination of metals which form simple amalgams (inter-metallic compounds must also be avoided). This limitation, however, introduces some desirable selectivity and most organic compounds will not interfere with the determination of the metals. Using acceptable deposition times, analysis of very low concentrations is possible. Certainly for heavy metal ions, the sensitivity of anodic stripping analyses compares well with that of atomic absorption spectroscopy even with non-flame atomization (see Table 11.4). Moreover, these data do not represent the ultimate detection limit since the plating time can be extended. 

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