Atomic Absorption Spectroscopy Questions and Answers

Answer: A

At around seven thousand kelvin no compound survives, so the refractory oxide problems that plague flame work simply do not arise. Oxygen from the sample itself is present, residence time is comparable, and the use of argon is why the temperature is achievable rather than the reason interferences are absent. Removing a whole class of interference by exceeding the conditions that create it is the plasma's fundamental advantage. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: B

Exciting every element produces thousands of lines, and overlaps between them are the plasma's characteristic problem, demanding a high-resolution spectrometer and careful line selection. Chemical suppression is largely absent, ionisation is severe but corrected by the technique's own standards, and viscosity affects both alike. A technique that measures everything at once must also cope with everything at once, which is where its complexity comes from. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: C

Comparing the Boltzmann factors at the two temperatures:

\[ \begin{aligned} \frac{e^{-2.1/kT_{p}}}{e^{-2.1/kT_{f}}} \\ &\approx \frac{0.032}{6\times10^{-5}} \end{aligned} \]

which is a factor of several hundred. That exponential dependence on temperature is why emission techniques gain so enormously from a hotter source, and why absorption, which relies on the ground state, gains almost nothing.

Answer: D

With essentially every atom already in the ground state, raising the temperature cannot increase that population appreciably - it can only reduce it slightly through ionisation. Lamp brightness and detector saturation are unrelated, and line broadening is a real but small effect. A measurement of a nearly saturated quantity is robust against the variable that saturates it, and here that robustness is the whole reason absorption displaced emission for most metals.

Answer: A

At nanogram levels the metal content of an ordinary reagent acid can exceed the amount being determined, so the blank swamps the sample. Tube attack, flame temperature and nebuliser blockage are lesser concerns. That the reagents become the dominant source of analyte as detection limits fall is a general feature of trace analysis, and it is why sub-boiling distilled acids exist as a product.

Answer: B

Ions adsorb onto glass at low concentration and leach from it at low pH, so both losses and contamination occur. Glass is not in the light path, resists most acids apart from hydrofluoric, and silicon is not usually the analyte. Plastic vessels, acid-washed and dedicated to the work, are the standard remedy, and the choice of container becomes a real part of the method at these levels.

Answer: C

Soaking in dilute nitric acid displaces metal ions bound to the surface and carries them away, leaving the vessel low in the analytes of interest. Sterilisation is irrelevant, roughening would make adsorption worse, and neutralisation is not the point. Preparing the container as carefully as the sample is what separates trace analysis from ordinary analysis, and it is the step most often skipped.

Answer: D

A blank taken through the same digestion, dilution and vessels as the sample measures everything the procedure itself contributes, which a simple instrument zero cannot. Flame stability and lamp alignment are checked separately. Measuring what a method contributes when no sample is present is the only way to know how much of a small result is real.

Answer: A

Adding a known amount of analyte to a sample and measuring how much is found tests the whole procedure for losses and suppression together, and a recovery near a hundred per cent is the evidence a method works on that matrix. Linearity, noise and blanks are checked separately. Testing a method against a known answer, in the actual matrix, is the most convincing validation available short of a certified reference material. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: B

A certified material is a real matrix - a soil, a food, an alloy - whose analyte content has been established by several laboratories and methods, so a result on it tests the whole procedure against an accepted value. A pure standard calibrates, a blank measures contamination, and wavelength is checked with a lamp. Validating against a material like the sample, rather than against a pure solution, is what distinguishes accuracy from precision. The shared properties explain why these belong to one family, and the differences explain why more than one exists.