Page 79 - Geochemistry of Oil Field Waters

ATOMIC ABSORPTION METHODS 67

while a premix burner is used for organic solutions. A nitrous oxide burner
head with. a 2-inch slot is used for determining aluminium, barium, and
beryllium because overheating is often encountered wit,h a 3-inch slot
burner.
The use of concentration steps, such as solvent extraction of a chelated
compound, enables sensitivities lower than those shown in Table 3.XII to be
achieved. For example, aluminium and beryllium can be complexed with
8-quinolinol and extracted with chloroform; cadmium and lead can be com-
plexed with ammonium pyrrolidine dithiocarbamate and extracted with
methyl isobutyl ketone. When burning the organic solvents, it usually is
necessary to reduce the fuel air ratio because the burning organic solvent
contributes to the fuel supply producing an undesirable luminescent flame
and may also lift the flame off the burner. An optimum fuel/air ratio can be
found by noting the characteristics of the flame before burning the organic
solvent and then reducing the fuel flow, while burning the organic solvent
until the flame characteristics are similar to those noted before the organic
solvent was burned. Ramirez-Munoz (1968) provides additional information.
Burner height is very important and adjustment often is necessary when
changing from one element to another. Some instruments have a Vernier
adjustment for reproducing burner-height settings and some do not. Fig. 3.5
illustrates a device which can be used for reproducing exact burner height
(Ballinger et al., 1972).

0-m from hollow cathode lamp

Fig. 3.5. Device for reproducing burner height for emission and atomic absorption spec-
trometers.