Page 111 - Geochemistry of Oil Field Waters

COLORIMETRIC METHODS 99

Ammonium citrate solution: dissolve 10 g of ammonium citrate in water
and dilute to 100 ml.
Hydroxylamine hydrochloride solution: dissolve 10 g of hydroxylamine
hydrochloride in water and dilute to 50 ml.

Procedure. Add 10 ml of ammonium citrate solution, and 5 ml of hydroxy-
lamine hydrochloride solution to a sample of effluent containing up to 100
pg of nickel, and adjust the pH to 8 with ammonium hydroxide. Transfer the
mixture to a 125-ml separatory funnel, add 10 ml of dimethylglyoxime
solution and 10 ml of chloroform, and shake the mixture vigorously for 1
minute. Let the phases separate and extract the chloroform phase into
another 125-ml separatory funnel. Make additional extractions of the sample
with 10-ml portions of chloroform until a colorless chloroform extract is
obtained. Add 10 ml of 4N ammonium hydroxide solution to the combined
chloroform extracts in the 125-ml separatory funnel, and shake the mixture
vigorously for 1 minute. Let the phases separate and discard the ammonium
hydroxide phase.
Acidify the chloroform phase with 1 ml of 6N hydrochloric acid, shake
the mixture vigorously for 2 minutes, let the phases separate, and discard the
chloroform phase. Add 10 ml of chloroform to the acid phase, shake the
mixture vigorously for 1 minute, and discard the chloroform phase. Adjust
the pH of the acid phase to 6.9, transfer it to a 100-ml volumetric flask, add
bromine water until a yellow color persists, swirl the mixture, and allow it to
stand for 10 minutes. Add 10 ml of 4N ammonium hydroxide and 10 ml of
dimethylglyoxime solution. Swirl to mix, cool to room temperature in an ice
water bath, and adjust to 100-ml volume with water. After 5 minutes deter-
mine the absorbance at 445 mp using a 1-cm cell and a spectrophotometer.

Calculations. Calculate the nickel concentration in the water by using a
calibration curve prepared by using about 10-100 pg of nickel:
pg Ni (from curve) = mg/l Ni+ ’
ml sample
Lead

Dithizone (Sandell, 1959, p. 665) is an excellent reagent for the determi-
nation of traces of lead. Lead dithizonate probably has a formula similar to
the following:
r
C6HS
I