(b) Preparation of calibration curve. Pipet 1.0, 2.0, 3.0, 4.0,
and 5.3 ml. of standard copper solution into 400 ml. beakers, and add 25
Carry along a reagent blank.
ml. of water and 2 ml. of perchloric acid.
Add 5 ml. of ammonium citrate solution (40 percent), 1 ml. of EDTA solution
Add ammonium hydroxide
(5 percent) and 2 drops of phenol red indicator.
until the solutions just change to red , cool , and wash into 125 ml.
separatory funnels whose sterns have been dried with wads of filter paper.
Add 5 ml. of sodium diethyldithiocarbamate solution (0.1 percent), and
Drain the chloroform layer
10 ml. of chloroform and shake for 1 minute.
into dry 25 ml. volumetric flasks, extract twice more with 5 ml. portions
of chloroform, and dilute the combined extracts to 25 ml. with chloroform.
Measure the transmittance at 435 millimicorns with a spectrophotometer
that has been set to 100 percent transmittance with the reagent blank.
Plot mg. of copper against percent transmittance on semi-log paper.