Analytical Method: Sulfate in chromium plating baths

Instruments and Reagents:
Cat.No. 173016  Spectroquant® VIS Spectrophotometer Prove 100 or
Cat.No. 173017  Spectroquant® UV/VIS Spectrophotometer Prove 300 or
Cat.No. 173018  Spectroquant® UV/VIS Spectrophotometer Prove 600 or
Cat.No. 109748  Spectroquant® Photometer NOVA 30 or
Cat.No. 109751  Spectroquant® Photometer NOVA 60 or
Cat.No. 173632  Spectroquant® Colorimeter Move 100
Cat.No. 114946  Rectangular cells 10 mm and/or
Cat.No. 114947  Rectangular cells 20 mm and/or
Cat.No. 114944  Rectangular cells 50 mm
Cat.No. 114548  Spectroquant® Sulfate Cell Test
Cat.No. 100617  Spectroquant® Sulfate Cell Test*
Cat.No. 114564  Spectroquant® Sulfate Cell Test
Cat.No. 100317  Hydrochloric acid 37 % for analysis 
Cat.No. 100316  Hydrochloric acid 25 % for analysis 
Cat.No. 105432  Ammonia solution 25 % for analysis 
Cat.No. 109532  MColorpHastTM pH-indicator strips pH 7.5 - 14
Cat.No. 109533  MColorpHastTM pH-indicator strips pH 5 - 10
Cat.No. 116754  Water for analysis 
*not compatible with Move 100
Sample preparation:
Place 2 ml bath sample in a 250-ml beaker, add 10 ml 37 % hydrochloric acid, cover with a watch glass and boil gently - in a fume cupboard - until all the Cr(VI) has been reduced to Cr(III). The sample will become dark green due to the effect of the released chlorine. Continue heating until acid fumes cease and a syrupy residue is left. Dissolve the residue in about 30 ml water for analysis and transfer the solution to a 50-ml volumetric flask. Adjust the pH to 8.5 - 9.5 with ammonia solution, checking with pH-indicator strips. Make up to the mark with water for analysis and mix. Filter off the precipitated chromium (as Cr(OH)3) and adjust the pH of the clear filtrate to pH 7 - 8 with as little as possible 25 % hydrochloric acid (volume error!).
Determine with the above mentioned test kits.
Sulfate content in mg/l SO4 = analysis value in mg/l SO4 x 25


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