Page 116 - Geochemistry of Oil Field Waters

104 ANALYSIS OF OILFIELD WATERS

Cadmium dithizonate in carbon tetrachloride absorbs strongly at a wave-
length of 620 mp.

Reagents. Standard cadmium solution: dissolve 0.100 g of cadmium metal in
hydrochloric acid and dilute to 1 liter with water. Pipet a 10-ml aliquot of
this stock solution into another l-liter volumetric flask and dilute to volume.
This solution contains 1 pg/ml of cadmium.
Ammonium chloride, 1N: dissolve 53.5 g of ammonium chloride in water
and dilute to 1 liter.
Rochelle salt solution: dissolve 100 g of rochelle salt (KNaC4H406 - 4H20)
in water and dilute to 1 liter.
Sodium citrate solution: dissolve 100 g of sodium citrate in water and
dilute to 1 liter.
Hydrogen peroxide, reagent grade 30% hydrogen peroxide.
Tartaric acid solution: dissolve 20 g of tartaric acid in 1 liter of water.
Store in a refrigerator and discard if any mold is present.
No.1 dithizone reagent: dissolve 0.12 g of dithizone in 1 liter of carbon
tetrachloride. Store in a refrigerator in a dark bottle.
No.2 dithizone reagent: dilute 5 ml of No.1 reagent to 100 ml with
carbon tetrachloride. Store in the refrigerator.
Hydroxylamine hydrochloride solution : dissolve 10 g of hydroxylamine
hydrochloride in 50 ml of water. Prepare fresh weekly.
Sodium hydroxide (35%)-potassium cyanide (1%) solution: dissolve 175 g
of sodium hydroxide and 0.5 g of potassium cyanide in water and dilute to 1
liter.
Ammonium hydroxide 5M: dilute 16.0 ml of concentrated ammonium
hydroxide (14.8M) to 50 ml.
Sodium hydroxide, 5% solution: dissolve 5 g of sodium hydroxide in
water and dilute to 100 ml.

Procedure. Filter the brine through Whatman No.4 filter paper (double
thickness). Transfer 900 ml or less of the filtered brine to a 2-liter beaker,
add 5 ml of 30% hydrogen peroxide, and heat until complete decomposition
of the excess hydrogen peroxide is attained. Cool the solution and filter if
any precipitate is present. Add 100 ml of ammonium chloride solution, 10
ml of rochelle salt solution, 25 ml of sodium citrate solution, and adjust the
pH to between 8 and 8.5 with 5M ammonium hydroxide. Transfer the
solution to a liter separatory funnel, add 15 ml of the No.1 dithizone solu-
tion, and shake the mixture vigorously for 5 minutes. Let the phases separate
and extract the dithizone phase into a 50-ml separatory funnel. Reextract
the brine with another 15 ml of No.1 dithizone solution. Separate the
dithizone phase into the 50-ml separatory funnel and discard the brine
phase.
Add 10 ml of tartaric acid solution to the combined dithizone extractions
in the 50-ml separatory funnel and shake the mixture vigorously for 2