Page 87 - Geochemistry of Oil Field Waters

ATOMIC ABSORPTION METHODS 75

reading on the recorder is greater than the 5-mg/l standard, aspirate the
9-mg/l standard through the burner until a maximum stable reading is ob-
tained. Record the reading and if the sample reading on the recorder is less
than the 5-mg/l standard, aspirate the 1-mg/l standard through the burner
until a maximum, stable reading is obtained, and record the reading.

Calculations:

where %A = percent absorption of high standard; %I2 = percent absorption
of low standard; %A, = percent absorption of sample; mg/ll = mg Mgt2 /1 of
high standard; mg/12 = mg Mg+2 /1 of low standard; mg/l, = mg Mg+2 /1 of
sample; and DF= dilution factor of sample (100/ml sample).
Derivation of above equation:

%A 1 -%A 2 - %A s-%A 2
-
mg/l1 -mg/l2 mg/l,-mg/l2

or :

when mg/l, = 11, mg/12 = 1; A mg/l(l-2) = 10
when mg/ll = 21, mg/12 = 11; A mg/l( -2 = 10
mg/ll -mg/12 = 10, when standards of 21 mg/l and 11 mg/l or 11 mg/l and
1 mg/l are used.

Calcium (2)

The same apparatus used in determining magnesium by atomic absorption
can be used to determine calcium.

Reagents. The necessary reagents are calcium standard solution, 1 mg/ml;
lanthanum solution, 1 g/ml; and hydrochloric acid.

Calcium standard working solutions

Pipet 1.0 ml of the calcium standard stock solution into a 1-liter flask, add
11.0 ml to a second 1-liter flask, and 21.0 ml to a third 1-liter flask. To each
flask add 50 ml of concentrated hydrochloric acid, and 10 ml of the
lanthanum stock solution, and dilute each to an overall 1,000 ml volume