Extraction-spectrophotometric determination of traces of mercury with Brilliant Green
1973 Volume 22 Issue 3 Pages 318-322
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1973 Volume 22 Issue 3 Pages 318-322
In acid and neutral solutions, Brilliant Green(C. I. 42040) which is in the R+ form, has been used to determine antimony, gold, rhenium and other metals.
A method has been developed for the spectrophotometric determination of microgram amounts of mercury, after extraction of mercury(II) from an aqueous solution into benzene with Brilliant Green (R+formed in acid solution) in the presence of potassium iodide.
Various factors such as pH, concentration of potassium iodide and Brilliant Green, volume ratio of two phases, shaking time, diverse ions, etc. have been studied, and the optimum conditions for the determination of mercury have been examined.
Mercury(II) in the presence of potassium iodide was found to react with Brilliant Green to form tetra iodomercurate-Brilliant Green ion-association complex, which can be extracted quantitatively into benzene in pH region between 0.7 and 1.5. The complex extracted was stable and had an absorption maximum at 640 nm. The molar ratio of mercury to Brilliant Green in the complex has been confirmed to be 1 : 2 by the continuous variation. The recommended procedures are as follows.
Place an aliquot of standard mercuric nitrate solution (or of sample solution), containing up to 20 μg of mercury(II), in a 50 ml separation funnel, and make the volume up to 21 ml with water. Add 3 ml of 0.1 M potassium iodide solution, 3 ml of 10-3M Brilliant Green solution, the pH of the solution is adjusted to 0.71.5 with 1.8 N sulfuric acid, and then make the final volume of the aqueous phase 30 ml. Extract the complex with 10.0 ml of benzene by shaking the two phases for 5 minutes. After the phases separate, transfer the organic layer into a stoppered glass bottle containing sodium sulfate, and then transfer into a 1 cm cell and measure the absorbance at 640 nm against the reagent blank.
Beer's law was obeyed over the range 0 to 20 μg of mercury. The molar ratio absorptivity of the complex at 640 nm was 1.0 × 105 and the sensitivity for log(I0/I) =0.001 was 1.7 × 10-3 μgHg/cm2. Perchlorate, thiocyanate and Fe(III) interfered with the determination seriously.
