Calibration atomic absorption spectrometry

A.F. Silva, D.L.G. Borges, F.G. Lepri, B. Welz, A.J. Curtius, U. Heitmann, Determination of cadmium in coal using solid sampling graphite furnace high-resolution continuum source atomic absorption spectrometry, calibration against aqueous standards and Ir as a permanent modifier, J. Anal. Atom. Spectrom. (2005) submitted. 

Koscielniak, R, Non-linear Robust Regression Procedure for Calibration in Flame Atomic Absorption Spectrometry, Analytica Chimica Acta 278, 1993, 177-187. 

Hofmann C, Vandecasteele C, Pauwels ] (1992) New calibration method for solid sampling Zeeman atomic absorption spectrometry (SS-ZAAS) for cadmium. Fresenius J Anal Chem 342 936-940. 

Pauwels J, Hofmann C, Vandbcasteele C (1994) Calibration of solid sampling Zeeman atomic absorption spectrometry by extrapolation to zero matrix. Fresenius J Anal Chem 348 418-421. 

Bishop [75] determined barium in seawater by direct injection Zeeman-modulated graphite furnace atomic absorption spectrometry. The V203/Si modifier added to undiluted seawater samples promotes injection, sample drying, graphite tube life, and the elimination of most seawater components in a slow char at 1150-1200 °C. Atomisation is at 2600 °C. Detection is at 553.6 nm and calibration is by peak area. Sensitivity is 0.8 absorbance s/ng (Mo = 5.6 pg 0.0044 absorbance s) at an internal argon flow of 60 ml/min. The detection limit is 2.5 pg barium in a 25 ml sample or 0.5 pg using a 135 ml sample. Precision is 1.2% and accuracy is 23% for natural seawater (5.6-28 xg/l). The method works well in organic-rich seawater matrices and sediment porewaters. 

The mathematical model may not closely fit the data. For example. Figure 1 shows calibration data for the determination of iron in water by atomic absorption spectrometry (AAS). At low concentrations the curve is first- order, at high concentrations it is approximately second- order. Neither model adequately fits the whole range. Figure 2 shows the effects of blindly fitting inappropriate mathematical models to such data. In this case, a manually plotted curve would be better than either a first- or second-order model. 

Non-linear concentration/response relationships are as common in pesticide residue analysis as in analytical chemistry in general. Although linear approximations have traditionally been helpful the complexity of physical phenomena is a prime reason that the limits of usefulness of such an approximation are frequently exceeded. In fact, it should be regarded the rule rather than the exception that calibration problems cannot be handled satisfactorily by linear relationships particularly as the dynamic range of analytical methods is fully exploited. This is true of principles as diverse as atomic absorption spectrometry (U. X-ray fluorescence spectrometry ( ), radio-immunoassays (3), electron capture detection (4) and many more. 

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 . 

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. 

M. Felipe-Sotelo, M. J. Cal-Prieto, M. P. Gomez-Carracedo, J. M. Andrade, A. Carlosena and D. Prada, Handling complex effects in slurrysampling-electrothermal atomic absorption spectrometry by multivariate calibration. Anal. Chim. Acta, 571(2), 2006, 315-323. 

E. M. M. Flores, J. N. G. Paniz, A. P. F. Saidelles, E. 1. Muller and A. B. da Costa, Direct cadmium determination in sediment samples by flame atomic absorption spectrometry using multivariate calibration procedures, J. Anal. At. Spectrom., 18, 2003, 769-774. 

D. C. Baxter and J. Ohman, Multi-component standard additions and partial least squares modelling, a multivariate calibration approach to the resolution of spectral interferences in graphite furnace atomic absorption spectrometry, Spectrochim. Acta, Part B, 45(4 5), 1990, 481 491. 

Y. Vander Heyden, P. Vankeerberghen, M. Novic, J. Zupan and D. L. Massart, The application of Kohonen neural networks to diagnose calibration problems in atomic absorption spectrometry, Talanta, 51(3), 2000, 455-466. 

E. A. Hernandez-Caraballo, F. Rivas and R. M. Avila de Hernandez, Evaluation of a generalized regression artificial neural network for extending cadmium s working calibration range in graphite furnace atomic absorption spectrometry. Anal. Bioanal. Chem., 381(3), 2005, 788-794. 

Ross et al. [6] analysed samples of soil leachates from laboratory columns and of soil pore water from field porous cup lysimeters for aluminium by atomic absorption spectrometry under two sets of instrumental conditions. Method 1 employed uncoated graphite tubes and wall atomisation method 2 employed a graphite furnace with a pyrolytically coated platform and tubes. Aluminium standards were prepared and calibration curves used for the colorimetric quantification of aluminium. Method 1 gave results which compared favourably with method 2 in terms of both sensitivity and interference reduction for samples containing 1-15 uM aluminium. 

After cooling, the condenser is rinsed with 30 ml water and the solution filtered into a 100 ml calibrated flask. The filter paper is rinsed five times with a few millilitres of warm (250 °C) 2M nitric acid. After cooling, the flask contents are made up to 100 ml with 2M nitric acid. The solution was then analysed for cadmium by atomic absorption spectrometry equipped with... 

In analytical spectrometry there are many types of calibration curves which are set up by measuring spectrometric reference solutions. The measurements yield a curve of absorbance versus concentration, and the points between the data of the reference solutions are interpolated by fitting a suitable curve, which normally follows the Beer-Lambert law and which gives rise to a straight line through the origin of the coordinate system. The measurement conditions and the results of the calibration curve evaluations in the case of chromium and lead measurements by electrothermal atomic absorption spectrometry are presented in Table 1. 

Fig. 2 The calibration curves for chromium measurement by atomic absorption spectrometry...

Determination of lead in water by atomic absorption spectrometry (AAS) The AAS instrument has be to calibrated using reference solutions made up by dissolving known amounts (balance) of a certified reference material (CRM) or a pure substance such as Pb(N03)2 in a de-... 

Mixtures of R3Sn+ compounds (R= -butyl. phenyl, cyclohexyl) were separated by ion exchange-high performance liquid chromatography-graphite furnace atomic absorption spectrometry [252], The small spread in calibration slopes in Fig. 4.10 signifies similar efficiencies for their separation and column recovery, as well as graphite furnace sensitivities. 

An example of a calibration curve for Cd with a Zeeman electrothermal atomization atomic absorption spectrometry (ET-AAS) is presented in Figure 6.1. A simple linear regression model is fitted through the data points. The response of the ET-AAS is placed on the ordinate and the concentration of the injected standard solutions on the abscissa. The concentration of the unknown samples can be calculated back as X = (Yt — a)/b. 

M. H. Canuto, H. G. Luna Siebald, G. Magela de Lima, J. B. Borda Silva, Antimony and chromium determination in Brazilian sugar cane spirit, cachaca, by electrothermal atomic absorption spectrometry using matrix matching calibration and ruthenium as permanent modifier, J. Anal. Atom Spectrom., 18 (2003), 1404-1406. 

The indirect method is a calibration approach complementary to the set of standards method in the sense that it allows determination of additional analytes with the use of a given detection system. For instance, it is often used for the determination of many anions in trace amounts by atomic absorption spectrometry [3]. It is interesting that the method gives a chance to positively exploit the interference effect. Reaction between the interferent and analyte in the set of standards method can be exploited such that the signal is measured for the analyte (now considered the reagent) and the interferent takes the role of analyte. 

Tyson, J.F., Bysouth, S.R. Network flow injection manifolds for sample dilution and calibration in flame atomic absorption spectrometry. J. Anal. At. Spectrom. 3, 211-215 (1988)... 

Whatever the analytical method and the determinand may be, the greatest care should be devoted to the proper selection and use of internal standards, careful preparation of blanks and adequate calibration to avoid serious mistakes. Today the Antarctic investigator has access to a multitude of analytical techniques, the scope, detection power and robustness of which were simply unthinkable only two decades ago. For chemical elements they encompass Atomic Absorption Spectrometry (AAS) [with Flame (F) and Electrothermal Atomization (ETA) and Hydride or Cold Vapor (HG or CV) generation]. Atomic Emission Spectrometry (AES) [with Inductively Coupled Plasma (ICP), Spark (S), Flame (F) and Glow Discharge/Hollow Cathode (HC/GD) emission sources], Atomic Fluorescence Spectrometry (AFS) [with HC/GD, Electrodeless Discharge (ED) and Laser Excitation (LE) sources and with the possibility of resorting to the important Isotope... 

It should be noted that when we used methods of measurement needing inorganic reference materials for calibration (such as flame photometry or atomic absorption spectrometry) the uncertainty due to the reference materials was considerably lower than that due to the photometric device. On the contrary, when we used a clinical reference material certified for its glucose concentration with a 10% (rel) uncertainty, this uncertainty exceeded twice the uncertainty due to the spec-trophotometric device. When we determined Mg by a spectrophotometric method with Titan Yellow, we found that the uncertainty due to the reference material was approximately twice that due the device, as we used a very accurate spectrophotometer. 

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