1. Lanthanum solution: Transfer 140 g of lanthanum oxide (La2O3, 99.997 percent pure) into a 2-L beaker. Slowly add 300 mL of concentrated hydrochloric acid, allowing time for the reaction to be completed after each addition of acid. Then, add 200 mL of distilled water. Each 4 mL of the final solution contains approximately 1 g of lanthanum.
2. Manganese stock solution: Transfer 0.3872 g of pure manganese metal into a glass beaker, add 20 mL of hot 8 M nitric acid, and gently boil the nitric acid for several minutes. After the resulting solution has cooled to room temperature, transfer the solution to a 500-mL volumetric flask and dilute to volume with distilled water. The concentration of MnO in this solution is 1,000 m g/mL.
3. Stock multiple-element standard solution: Transfer 0.8924 g of CaCO3, 0.9435 g of NaCl, 0.7915 g of KCl. and 2.4556 of FeSO4(NH4)2SO4· 6H2O, (all reagent-grade purity) and 0.3045 g of magnesium ribbon to a 500-mL volumetric flask. (Magnesium ribbon generally is 99 percent magnesium; therefore, the weight of the ribbon includes a 1-percent correction.) Add 50 mL of distilled water and 10 mL of concentrated hydrochloric acid. Boil the dilute acid to dissolve all the constituents. After the solution cools to room temperature, add 50.0 mL of the manganese stock solution (1,000 m g/mL of MnO), dilute to volume with distilled water, and thoroughly mix the final solution. This solution contains the equivalent of 1.00 mg/mL each of Fe2O3, CaO, MgO, Na2O, and K2O, and 0.1 mg/mL of MnO.
4. Working standard solutions: To six 250-mL volumetric flasks, add 0, 6, 12, 18, 24, and 30 mL of the standard stock solution. Then, add 1.2 g of flux mixture, 5 mL of 8 M nitric acid, and approximately 200 mL of distilled water. Agitate the nitric acid solution to dissolve the flux mixture. Then, add distilled water to make the final volume 250 mL and make the solution homogeneous by vigorous mixing. These six solutions represent a blank and 3-, 6-, 9-, 12-, and 15-percent (equivalent in the sample) standard solutions. For MnO, the same six solutions represent a blank and 0.3-, 0.6-, 0.9-, 1.2-, and 1.5-percent standard solutions.
Procedure for Calcium, Iron, Magnesium, and Manganese
1. Transfer 0.750 mL of blank, sample, and standard solutions into small vials or beakers.
2. Dilute 8 mL of lanthanum solution with 200 mL of distilled water. Add 6.5 mL of this solution to all standards, samples, and blanks.
3. Calibrate the atomic absorption spectrometer by setting the concentration scale to zero for the recommended wavelength (table 16) while the blank solution is nebulized into the flame. Then, set the concentration scale with the 6-percent working standard, and verify this setting with solutions of silicate standards. Directly measure the concentrations of calcium, iron, magnesium, and manganese in each of the samples. Most available atomic absorption spectrometers are suitable for these measurements; the optimum operating conditions for each element usually are discussed in the manual provided with the spectrometer. Importantly, the individual measurements of concentration (or, absorbance) for a sample should be "bracketed" between those of standards because the instrumental responses are usually not linear.
Procedure for Potassium and Sodium
1. Transfer 0.200 mL of blank, sample solutions, working standards, and silicate standards into a small vial or beaker.
2. Dilute 1.2 mL of lanthanum solution with 200 mL of distilled water. Add 5.0 mL of this solution to the blank and to each of the standards and samples.
3. Calibrate the atomic absorption spectrometer using the concentration mode with the 6-percent working standard, and check appropriate silicate standards for known values. Measure directly the concentration of samples.
Methods based on AAS and spectrophotometry provide accurate determinations of 10 inorganic elements in coal ash. Although not as rapid as X-ray fluorescence (XRF) spectrometry, these methods furnish an approach to determining major oxides in coal ash that is both inexpensive and accurate (table 18). The agreement between our measurements and the NBS-certified concentrations for10 elements in NBS 1633a coal fly ash, demonstrated by data in table 18, is quite acceptable. Results from XRF spectrometry for SiO2, Al2O3, and Fe2O3 in ash sample number 1 and for SiO2 in sample number 7 (table 18) are outside the range covered by the standards used for calibration. Thus, extrapolations beyond this range could introduce error into these determinations.
Bunting, W.E., 1944, The determination of soluble silica in very low concentrations: Industrial and Engineering Chemistry (analytical ed.), v. 16, p. 612-615.
Parker, C.A., and Goddard, A.P., 1950, The reaction of aluminum ions with alizarin-3-sulfonate, with particular reference to the effect of calcium ions: Analytica Chimica Acta, v. 4, no. 5, p. 517-536.
Shapiro, L., 1975, Rapid analysis of silicate, carbonate, and phosphate rocks: U.S. Geological Survey Bulletin 1401, revised ed., 76 p.
Yoe, J.H., and Armstrong, A.R., 1947, Colorimetric determination of titanium with disodium-1,2-dihydroxybenzene-3,5-disulfonate: Analytical Chemistry, v. 19, p. 100-102.
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