Page 109 - Geochemistry of Oil Field Waters

COLORIMETRIC METHODS 97

This reagent is used to determine copper because of its nearly specific reac-
tion with cuprous copper. The combining ratio is 2 moles of neocuproine to
1 mole of copper. The increased selectivity of neocuproine for copper is
caused by a steric hindrance effect. The cuprous neocuproine compound is
formed over a pH range of 3-10 and is bright orange. The compound can be
extracted with n-amyl alcohol, isoamyl alcohol, n-hexyl alcohol, or chloro-
form. The maximum absorption of the compound in isoamyl alcohol occurs
at a wavelength of 454 mp.
Hydroxylamine hydrochloride can be used to reduce the cupric ion to
cuprous. Citrate will hold any iron present in solution when the pH is
adjusted to between 5 and 6. The chromate ion can cause low results; how-
ever, this effect does not occur when iron is present, which is almost always
the case with an oilfield brine. The anions such as sulfide, cyanide, periodate,
nitrate, t hiocyanate, and ferricyanide can interfere by reacting with
hydroxylamine; however, they are eliminated in the ion exchange separation.

Reagents. Neocuproine solution: dissolve 1 g of 2,9-dimethyl-l,1 O-phenan-
throline in 1 liter of ethyl alcohol.
Hydroxylamine hydrochloride solution : dissolve 10 g of hydroxylamine
hydrochloride in 100 ml of water.
Isoamyl alcohol, analytical reagent grade.
Sodium citrate solution: dissolve 300 g of sodium citrate in 1 liter of
water, add 2 ml of the hydroxylamine hydrochloride solution, add 1 ml of
neocuproine solution, and extract with 10-ml portions of chloroform until a
colorless chloroform extract is obtained.
Standard copper solution: dissolve 0.100 g of copper in 5 ml of nitric acid
and 5 ml of water by heating gently to dissolve the copper. Add 5 ml of
perchloric acid and evaporate to fumes of perchloric acid. Cool, dilute with
water, transfer to a l-liter volumetric flask, and dilute to volume. Pipet a
100-ml aliquot of this solution to another l-liter volumetric flask. Dilute to
volume with water. This solution contains 10 mg/ml of copper.
Sodium acetate.

Procedure, Add 5 ml of 10% hydroxylamine hydrochloride solution and 20
ml of 30% sodium citrate solution to a sample of effluent from the ion
exchange column containing 4-150 pg of copper, and adjust the pH of the
mixture to between 5 and 6 with 1 g or more of sodium acetate. Extract
with a 10-ml portion of isoamyl alcohol. Separate the liquids and discard the
alcohol layer. Add 10 ml of 0.1% neocuproine solution and 10 ml of isoamyl
alcohol, and shake the mixture vigorously for 1 minute. Let the phases
separate and transfer the alcohol layer to a 50-ml volumetric flask. Make
additional extractions until the alcohol layer remains colorless. Dilute the
combined alcohol extracts to 50 ml with isoamyl alcohol, mix, and measure
the absorbance at 454 mp in a l-cm cell with a spectrophotometer.