Page 100 - Geochemistry of Oil Field Waters

88 ANALYSIS OF OILFIELD WATERS

I I I I 1 I I
I'
0.2 0.4 0.6 0.8 1.0 2.0 4.0 t 0
INTENSITY RATIO
Fig. 3.10. Calibration curve for emission spectrometry.

To obtain data for calibration curves for barium, boron, iron, manganese,
and strontium, use size 50-ml volumetric flasks. To one flask add no stan-
dard solution; add 1.0 ml to the second flask; and add 2.5 ml, 5.0 ml, 7.5 ml,
and 10.0 ml of standard solution to the third, fourth, fifth, and sixth flasks,
respectively. (These aliquots will vary with the sensitivity of your instru-
ment.) Add 2 ml of concentrated hydrochloric acid, 2 ml of internal stan-
dard solution, 5 d of synthetic brine solution, 20 ml of n-propanol, and
sufficient distilled water to adjust the final volume to 50 ml at ambient
temperature. For optimum accuracy, prepare duplicate or triplicate samples.
Aspirate and burn the samples using the excitation conditions, the
development conditions, and the microphotometer conditions described
above; plot the curves using the above procedure.
The water sample should be adjusted to a pH of about 1.5 at the time of
sampling to prevent precipitation and adsorption. The sample should be
contained in a good quality plastic bottle that has been rinsed first with
dilute nitric acid and then with distilled water.
Transfer to a 50-ml volumetric flask an aliquot of the sample of sufficient
size to provide absolute quantities of the elements which will fall within the
calibration curves. The optimum aliquot size will vary from brine to brine;
however, equal-size aliquots often can be used for waters with similar
specific gravities from the same geologic formation. Add 2 ml of concen-
trated hydrochloric acid, 2 ml of internal standard solution, 5 ml of
synthetic brine solution (or try to approximate the ionic composition of the