Page 34 - Geochemistry of Oil Field Waters

PRELIMINARY SAMPLE TREATMENT 23

Standard solutions

Examples of standardization procedures are given for some of the
methods. The concentrations of standard solutions are indicated as the
weight of a given element equivalent to, or contained in, 1 ml of solution.
The strength of acids and bases are given in terms of molarities or normali-
ties.

Accuracy of measurements

In the instructions for making the analysis and preparing the solutions,
significant figures are utilized to define the accuracy of weights and
measures.
Required accuracy for measurement of volume in the analysis and prepa-
ration of reagents is also shown. Standard solutions are prepared in and
measured from volumetric glassware.

Reagent chemicals and solutions

All of the chemicals used in the analytical procedures should conform to
the specifications of the Committee on Analytical Reagents of the American
Chemical Society. Chemicals not listed by this organization can be tested
according to procedures given by Rosin (1955). Primary standard chemicals
can be obtained from the National Bureau of Standards or from companies
marketing chemicals of the same purity.
Water used to dilute samples or to prepare chemical solutions should first
be demineralized by passage through mixed cation-anion exchange resins or
by distillation. Its specific conductance at 25°C must not exceed 1.5 pmho/
cm, and it should be stored in polyethylene bottles.
Carbon-dioxide-free water may be prepared by boiling and cooling
demineralized water immediately before use. Its pH should be between 6.2
and 7.2.
Ammonia-free water should be prepared by passing distilled water through
a mixed-bed ion-exchange resin.

Sampling

A field-filtered acidified sample also should be taken. It is pressured
filtered using a 0.45-pm membrane filter and then the filtrate is immediately
acidified to a pH of 3.0 or less with reagent-grade HCl. The acidified sample
is used for the following determinations: (1) aluminum, (2) arsenic, (3)
barium, (4) cadmium, (5) calcium, (6) copper, (7) iron, (8) lead, (9) magne-
sium, (10) manganese (11) nickel, (12) strontium, and (13) zinc.