Spectrophotometric, Conductometric Titration Method For The Determination Of Selenium, Iodine Content

A new method was developed based on the chromogenic reaction of selenite withmagnesonⅠin KCl-HCl buffer solution (pH2.0) using SDBS as a solubilizer. The color ofmagnesonⅠcould be faded by oxidation of selenite, and the absorbency was proportionalto the concentration of selenium in the range of 1-8μg/10mL. The maximum absorption ofcolor solution was at 450 nm with the apparent molar absorptivity of 3.73×10⁴L·mol^-1·cm^-1. The limit of detection was 0.13μg/mL for selenium. The proposed methodwas successfully applied to determine selenium in salt fortified with selenium.Repeatability of the determination, expressed as relative standard deviation (RSD) for 5determinations, was 0.26 % for 3.79μg/g of selenium measured.A new method was developed based on the chromogenic reaction of selenite withmagnesonⅠin borax buffer solution (pH 9.6). The results showed that selenite could reactwith borax and magnesonⅠto form a stable complex, the association ratio of which was1:4:7. The linear calibration range was 1-14μg/10mL for selenium determination. Theapparent molar absorptivity was found to be 3.73×10⁴ L·mol^-1·cm^-1 at 560 nm. The limitof detection was 0.20μg/mL for selenium. The proposed method was successfully appliedto determine selenium in salt fortified with selenium, and RSD for 5 determinations, was1.53% for 3.80μg/g of selenium measured.A new method for determination of selenium by double-peak-double-wavelengthspectrophotometry was developed. It was shown that in the NaHCO₃-NaOH buffersolution (pH 10.8), selenite could react with sodium bicarbonate and magnesonⅠto form astable complex, the association ratio of which was 1:4:6. And the complex exhibited apositive absorption peak at 448 nm and a negative absorption peak at 560nm.△A (△A=A_560nm-A_448nm, vs.water) was proportional to the concentration of selenium in the range of1-14μg/10mL. The apparent molar absorptivity was found to be 3.87×10⁴L·mol^-1·cm^-1. Itwas successfully applied to determine selenium in salt fortified with selenium, and RSDfor 5 determinations, was 0.44 % for 3.81μg/g of selenium measured.A new method was developed based on the reaction of selenite with L-ascorbic acid.Selenite could be reduced to elemental selenium forming stable suspension by L-ascorbicacid in hydrochloric acid with the the presence of glycerol. Nephelometry for seleniumdetermination with spectrophotometer was developed. The linear calibration range was0～100μg/10mL for selenium determination. The limit of detection was 0.029μg/mL forselenium. It was successfully applied to determine selenium in salt fortified with seleniumand health balance salt, and RSD for 5 determinations, were 1.16% for 3.84μg/g of selenium and 1.26% for 4.33μg/g of selenium measured respectively.A new method for determination of iodine by double-peak-double-wavelengthspectrophotometry was developed. In the presence of PVA-124, dissociation ofion-association complex of silver(Ⅰ)-phen-TBF was accelerated by the deposition reactionbetween iodide and silver ion in acetate buffer solution (pH 4.5), which exhibiting apositive absorption peak at 514nm and a negative absorption peak at 548nm.ΔA (ΔA=A_514nm-A_548nm, vs. reagent blank) was proportional to the concentration of iodine in therange of 1.25-10μg/25mL. The apparent molar absorptivity was found to be 1.18×10⁵L·mol^-1·cm^-1. The method was successfully applied to the determination of iodine in salt.In order to eliminate the effect of a great deal of sodium chloride on the determination ofiodine in salt sample, the approaching quantity of sodium chloride was added, thenemendated the working curve. The apparent molar absorptiviry became lower than theformer, which is 7.40×10⁴L·mol^-1·cm^-1, but it still could meet the needs of sample analysis,and RSD for 5 determinations was 3.1% for 36.1μg/g of iodine measured.A new method for determination of iodine by conductimetric titration was developed.Barium chloride lead acetate, silver nitrate and bluestone were used as titrants respectively.According to the titrant, the concentration of KIO₃ were in range of 1×10^-3～2.5×10^-3mol·L^-1, 8×10^-5～1.5×10^-4mol·L^-1, 1×10^-4～5×10^-4 mol·L^-1and 1.5×10^-3～5×10^-3 mol.L^-1respectively. The relative error under optimum condition were 2.11%,1.87%,1.75%, and1.45% respectively. The content of iodine in salt was determined successfully by thismethod.