Atomic absorption spectroscopy standardizing method

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). 

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. 

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. 

Investigation of atomic spectra yields atomic energy levels. An important chemical application of atomic spectroscopy is in elemental analysis. Atomic absorption spectroscopy and emission spectroscopy are used for rapid, accurate quantitative analysis of most metals and some nonmetals, and have replaced the older, wet methods of analysis in many applications. One compares the intensity of a spectral line of the element being analyzed with a standard line of known intensity. In atomic absorption spectroscopy, a flame is used to vaporize the sample in emission spectroscopy, one passes a powerful electric discharge through the sample or uses a flame to produce the spectrum. Atomic spectroscopy is used clinically in the determination of Ca, Mg, K, Na, and Pb in blood samples. For details, see Robinson. 

Salem et al. [48] reported simple and accurate methods for the quantitative determination of flufenamic, mefenamic and tranexamic acids utilizing precipitation reactions with cobalt, cadmium and manganese. The acidic drugs were precipitated from their neutral alcoholic solutions with cobalt sulfate, cadmium nitrate or manganese chloride standard solutions followed by direct determination of the ions in the precipitate or indirect determination of the ions in the filtrate by atomic absorption spectroscopy (AAS). The optimum conditions for precipitation were carefully studied. The molar ratio of the reactants was ascertained. Statistical analysis of the results compared to the results of the official methods revealed equal precision and accuracy. The suggested procedures were applied for determining flufenamic, mefenamic and... 

A Modified Standard Addition Method for Determining Cadmium, Lead, Copper, and Iron in Sea Water Derived Samples by Atomic Absorption Spectroscopy... 

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 standard addition method is commonly used in quantitative analysis with ion-sensitive electrodes and in atomic absorption spectroscopy. In TLC this method was used by Klaus 92). Linear calibration with R(m=o)=o must also apply for this method. However, there is no advantage compared with the external standard method even worse there is a loss in precision by error propagation. The attainable precision is not satisfactory and only in the order of 3-5 %, compared to 0.3-0.5 % using the internal standard method 93). 

Finally, it is recommended that for inductively coupled plasma (ICP) analysis a final filtration (0.45 xm) is carried out in order to prevent nebulizer blockages. If graphite-furnace atomic absorption spectroscopy (GFAAS) is the method of analysis, it is recommended that the standard additions method of calibration is used (see Chapter 1). 

Calcium Analysis. Materials for calcium analysis were ashed in an electric muffle furnace at 600°C. for 2 hours. The ash after weighing was dissolved in 4N nitric acid and the calcium content of the solution was determined by atomic absorption spectroscopy using standard methods. 

The optimal calcination method for zeolite beta was established by thermogravimetric analysis using a PL-Thermal Sciences STA 1500 apparatus. Chemical compositions of the zeolites were determined by atomic absorption spectroscopy on a Varian AAIO spectrometer after dissolution of the samples in hydrofluoric acid. The structure was confirmed by x-ray diffraction on a Siemens D-5000 diffractometer and with infrared spectroscopy on a Mattson Instruments Galaxy 2000 spectrometer. Total surface area, micropore area and micropore volume of the samples were determined by argon adsorption on a Micromeritics ASAP 200M volumetric analyzer using standard techniques. Crystal diameters were determined by scanning electron microscopy. 

The standard-addition method, which was described in Section ID-3, is widely used in atomic absorption spectroscopy lo partially or completely compensate for the chemical and spectral inlcrfcrcncc.s introduced by the. sample matrix. 

Iron in iron ores can, of course, also be analyzed by the classical redox titration with standard dichromate solution using a diphenylamine sulfonate indicator. Trace manganese in ores can also be determined using colorimetric methods or atomic absorption spectroscopy. An atomic absorption spectrophotometer, however, will cost a minimum of about 4500 and requires the periodic replacement of expensive hollow-cathode lamps. The point is that one usually has some choice of analytical methods, each with its particular advantages and disadvantages for the problem at hand. 

The comparison of detection limits Is a fundamental part of many decision-making processes for the analytical chemist. Despite numerous efforts to standardize methodology for the calculation and reporting of detection limits, there is still a wide divergence In the way they appear in the literature. This paper discusses valid and invalid methods to calculate, report, and compare detection limits using atomic spectroscopic techniques. Noises which limit detection are discussed for analytical methods such as plasma emission spectroscopy, atomic absorption spectroscopy and laser excited atomic fluorescence spectroscopy. 

Because of its extraordinary high sensitivity and specificity mass spectrometry has become a standard tool besides other powerful analytical methods for the trace analysis of metals, such as emission spectroscopy, atomic absorption spectroscopy, neutron activation analysis or electrochemical mediods. 

Electrolyte and trace element determinations in the urine were varried out by flame atom absorption spectroscopy. Only by this method and by using a long suction time of 6-8 ml is it possible to determine the very low copper concentrations. This allows calculation of mean values with low mean standard deviations (RSD) from numerous single values of the digital multimeter. An attenuation of at least 3 seconds is recommended, as copper concentrations in the urine are slightly above the sensitivity limit of flame spectroscopy. Under these technical conditions it is advantageous to use the flame rather than the graphite tube cuvette. 

FIGURE 9-19. Standard addition method for the determination of the concentration of an unknown. [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. Used by permission of Marcel Dekker Inc.]... 

Chemical and ionization interferences frequently found in atomic absorption spectroscopy are suppressed in ICP analysis. Since all samples are converted to simple aqueous or organic matrices prior to analysis, the need for standards matched to the matrix of the original sample is eliminated. The requirement that the sample presented to the instrument must be a solution necessitates extensive sample preparation facilities and methods. More than one sample preparation method may be necessary per sample depending on the range of elements requested. Spectral interferences can complicate the determination of trace... 

Atomic absorption spectroscopy is a preferred method in clinical chemistry. However, UV/Vis spectrometry by use of chelating methods combined with photometry of chromophores offers simple and fast approaches. Examples are methods recommended by the National Committee for Clinical Laboratory Standards (NCCLS 1990) taking ferrocene for Fe, eliminating interferences by Cu by addition of thiourea. Mg is determined by addition of xylidyl blue, Ca by use of o-cresolphthalein or arsenazo complexes. Interferences by Mg are reduced by addition of 8-hydroxyquinoline. Further chromophores and complexing agents are discussed in subsequent chapters and elsewhere [39]. 

The polymer is ashed in platinum. A nitric acid extract of the ash is examined by atomic absorption spectroscopy for concentrations of nickel, copper, zinc, iron, manganese, lead, cadmium and chromium at specific wavelengths. The method is calibrated against standard Solutions of the heavy metals in nitric acid. 

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