Determination of nickel by synergistic extraction

Determination. To an aliquot of the silver(I) solution containing between 10 and 50 pg of silver, add sufficient EDTA to complex all those cations present which form an EDTA complex. If gold is present ( 250 xg) it is masked by adding sufficient bromide ion to form the AuBr4 complex. Cyanide, thiocyanate or iodide ions are masked by adding sufficient mercury(II) ions to complex these anions followed by sufficient EDTA to complex any excess mercury(II). Add 1 mL of 20 per cent ammonium acetate solution, etc., and proceed as described under Calibration. 

(1) More rapid clarification of the nitrobenzene extract is obtained if the beakers contain about five pellets of sodium hydroxide. The latter is, however, a source of instability of the colour system and its use is, therefore, not recommended. 

Procedure. To 10 mL of a solution (Note 2) containing from 1 to 10 pg of nickel(II) add 5mL of a phthalate or acetate (ethanoate) buffer of pH 6.0 or, if the sample solution is acidic, use dilute ammonia to adjust the pH. To this solution now add 15mL of a chloroform solution of dithizone (7 x 10-5M) and 1,10-phenanthroline (3 x 10-5M). Shake the phases for five minutes in a 

(1) The reagent solution should be freshly prepared using analytical-grade dithizone and 1,10-phenanthroline, preferably taken from new or recently opened reagent bottles. 

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