Question

The measurement of Li in brine (salt water) is used by geochemists to help determine the origin of this fluid in oil fields. Flame atomic emission and absorption of Li are subject to interference by scattering, ionization, and overlapping spectral emission from other elements. Atomic absorption analysis of replicate samples of a marine sediment gave results in the table.

(a) Suggest a reason for the increasing apparent concentration of Li in samples 1 through 3 .

(b) Why do samples 4 through 6 give an almost constant result?

(c) What value would you recommend for reporting the real concentration of Li in the sample?

Short answer

1. As a result, the interfering species in experiment 2 do not interact as much as they did in experiment 1.
2. As a result, the hotter flame (higher temperature) is the cause of the constant results in tests 4 to 6.
3. As a result, the true value can be calculated by averaging the two experiments 3 and 6. This is the same as the 81.4ppm.

Step-by-step solution

Definition of Li

• Lithium is a soft, silvery-white metal that belongs to group 1 of the periodic table of elements, the alkali metals.
• It has a strong reaction with water. It's difficult to keep it safe. Because it is less thick and floats, it cannot be stored under oil like sodium.

Determine the increasing apparent concentration of Li in samples 1 through 3 .

(a)

• It is necessary to speculate on the cause of the apparent increase in Li content in samples 1 through 3.
• In comparison to experiment 1, the result in experiment 2 is better. This is due to the influence of interfering species being diluted. As a result, the interfering species in experiment 2 do not interact as much as they did in experiment 1.
• Dilution reduces the concentration of species that can react with Li or produce smoke, which scatters light.
• The amount of interference present in experiment 3 is the same as it was in experiment 2. In experiment 3, however, the interference is corrected using the standard addition approach.
• Standard addition is used to apply the effect of the complex interfering matrix to the known quantities of analyte.

Draw the samples 4 through 6 give an almost constant result

(b)

• The nearly constant results found in samples 4 to 6 must be explained.
• In comparison to experiments 1 to 3, experiment 4 to 6 uses a hotter flame. The higher temperature removes the interference that was present at the lower temperature.
• The interfering species' dilution has just a minor impact on the outcome. As a result, the hotter flame (higher temperature) is the cause of the constant results in tests 4 to 6.

Determine the real concentration of Li in the sample

(c)

• It is necessary to make a recommendation for reporting the true concentration of Li in the sample.
• We can deduce from the results of tests 1 to 3 that the usual addition produces a correct result. 3 and 6 are the experiments that are inside the experimental error limit.
• As a result, the true value can be calculated by averaging the two experiments 3 and 6. This is the same as the 81.4 ppm.