Page 73 - Geochemistry of Oil Field Waters

FLAME SPECTROPHOTOMETRIC METHODS 63

NITROBENZENE NITROETHANE I- NITROPROPANE 2- NITROPROPANE

1

Fig. 3.4. Relative intensities obtained by burning organic solvents containing tetraphenyl-
boron salts of cesium and rubidium.

Standard-addition technique to determine rubidium

Some waters contain sufficient rubidium to enable use of the standard-
addition technique. To analyze such waters, preliminary calibration curves
similar to those used to determine lithium (Fig.3.2) are recommended, to aid
in selecting the optimum amount of standard rubidium solution to use.

Manganese

The amounts of sodium, potassium , calcium, and strontium in most
petroleum-associated waters are too high to permit determination of man-
ganese with the flame spectrophotometer without preliminary separations.
These interferences can be obviated by extracting the manganese into a
chloroform 8-hydroxyquinoline solution. The chloroform is removed by
evaporation, and the manganese hydroxyquinoline is dissolved in n-propanol.
This solution is burned in the flame spectrophotometer, and the emission
intensity of its resonance triplet at 403.2 mp is recorded (Collins, 1962).

Reagents. The necessary reagents are standard manganese solution (dissolve
0.583 g of manganese dioxide in 10 ml of hydrochloric acid and dilute to 1
liter with distilled water, transfer a 100-ml aliquot of this solution to another