Thorium standard curve

A calibration curve for the range 0.2-10 mg fluoride ion per 100 mL is constructed as follows. Add the appropriate amount of standard sodium fluoride solution, 25 mL of 2-methoxyethanol, and 10 mg of a buffer [0.1 Af in both sodium acetate and acetic (ethanoic) acid] to a 100 mL graduated flask. Dilute to volume with distilled water and add about 0.05 g of thorium chloranilate. Shake the flask intermittently for 30 minutes (the reaction in the presence of 2-methoxyethanol is about 90 per cent complete after 30 minutes and almost complete after 1 hour) and filter about 10 mL of the solution through a dry Whatman No. 42 filter paper. Measure the absorbance of the filtrate in a 1 cm cell at 540 nm (yellow-green filter) against a blank, prepared in the same manner, using a suitable spectrophotometer. Prepare a calibration curve for the concentration range 0.0-0.2 mg fluoride ion per 100 mL in the same way, but add only 10.0 mL of 2-methoxyethanol measure the absorbance of the filtrate in a 1 cm silica cell at 330 nm. 

Figure 6.24 Calibration curves for uranium (a) and thorium (b) determination in brain samples via the standard addition mode using micronebulization in LA-ICP-MS. (/. S. Becker et ai, Anal. Chem. 77, 3208 (2005). Reproduced by permission of American Chemical Society.)...

Fluoride samples of high concentration can be titrated potentiometrically [60] with lanthanum nitrate or thorium nitrate reagent. The potentiometric standard addition technique with NaF standard solution [61] also was found applicable however, direct potentiometry using calibration curves is most often relied on in water analysis. 

Comparison of EOS data of thorium from different sources, showing also the effects of different EOS forms on the least-squares fitted parameters and KJ,. Unrestricted standard deviations of the correlated parameters are placed in parentheses and refer to the last decimal places of the parameter values, denotes the standard deviation of the data from the fitted curves and e gives the correlation coefficient for the fitted parameters and K. The usual (restricted) errors can be obtained by multiplication of the unrestricted errors with (1 — Parameters predetermined by the use of a second-order EOS form or by effective first-order fits using BE2, H02, and H12 with K(, fixed, are placed in obtuse brackets. 

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