Page 92 - Geochemistry of Oil Field Waters

80 ANALYSIS OF OILFIELD WATERS

Calculations. See calculations under “Lithium” in the flame spectrophoto-
metric section, Fig. 3.3, or Table 3.XI:

mg Fe x 1,000
ml sample = mg/l Fe+’
Precision. In a single laboratory using oilfield water samples containing con-
centrations of 6.3 and 6.8 mg Fe+2 /1, the standard deviations were k0.5 and
k0.3, respectively. The recoveries were 115.6% and 97%, respectively.

copper
Copper is determined at the 3247.5 8 wavelength with an air-acetylene
flame.

Reagents. The necessary reagent is a standard copper solution: obtain com-
mercially or dissolve 1.000 g of copper metal in a minimum volume of (1 +
1) nitric acid. Dilute 1 liter with 1% (v/v)’ nitric acid. 1 ml of solution
contains 1 mg of copper.

Preliminary calibration. Prepare standard copper solutions containing 1-5
pg/ml using the standard copper solution and 50-ml volumetric flasks.
Aspirate these standards and a blank as recommended in the calcium method
and determine the absorbance at a wavelength of 3247.5 8.

Procedure. Transfer an aliquot containing about 0.05 mg of copper to a
50-ml volumetric flask. Dilute to volume and aspirate. Calculate the approxi-
mate sample concentration from the preliminary calibration readings and
determine the aliquot size that will contain 0.05 mg of copper.
Transfer equal aliquots containing about 0.05 mg of copper to three 50-ml
volumetric flasks. Add no copper to the first flask, 0.05 mg of the copper
standard to the second flask, and 0.10 mg to the third. Dilute to volume.
Aspirate and record the absorbance readings for each sample.

Calculations. See calculations under “Lithium” in the flame spectrophoto-
metric section, Fig. 3.3, or Table 3.XI:
mgCux 1,000
ml sample = mg/l CU+’

Precision. In a single laboratory using an oilfield water sample containing a
concentration of 3 mg Cu+’ /1, the standard deviation was k0.2. The recovery
was 100.5%.

zinc

Zinc 1- determined at the 2138.6 A wavelength with an air-acetylene
flame.