Atomic Absorption Spectroscopy Questions and Answers

Answer: C

The first three are correct and the fourth confuses two ideas: sensitivity is the slope of the calibration, how much signal a concentration produces, while the lowest measurable concentration is the detection limit. Two instruments of equal sensitivity can differ widely in detection limit if one is noisier. Keeping slope and noise separate is what lets an improvement be attributed to the right cause. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: D

This is an ionisation suppressant, which works by flooding the flame with electrons and pushing the analyte's ionisation equilibrium back towards neutral atoms. A releasing agent addresses chemical interference, background correction addresses spectral interference, and a matrix modifier belongs to furnace work. Four remedies for four kinds of interference, each named after what it addresses. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: A

Fluorescence is not an interference here - it is the basis of a separate technique, atomic fluorescence spectroscopy, and any light the atoms emit is removed by the chopper along with the flame's own glow. The other three are the standard spectral, ionisation and physical interferences. That the chopper disposes of every steady emission is why the list of interferences is shorter than it might be. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: B

In fluorescence the atoms absorb the source's line and then radiate, and the emitted light is measured at right angles to the beam so the source itself is not seen. Thermal emission is flame photometry, elastic scattering is a background, and continuum absorption is not the arrangement. Measuring against a dark background rather than as a small difference between two large signals is what gives the technique its very low detection limits. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: C

Absorption measures a small difference between two large intensities, where the noise on the large ones dominates, while fluorescence measures a small signal against essentially nothing. The atoms, the atomiser and the need for a source are the same. Whether a measurement is a difference or an absolute reading decides how its noise behaves, and that is the whole of the advantage here.

Answer: D

Collisions with flame gases de-excite the atoms without radiation, so much of the fluorescence is lost and the promised sensitivity is not realised in an ordinary flame. It is single-element like absorption, uses a line source, and has a wide linear range. The technique found its niche with mercury and the hydride-forming elements, where a cool cell avoids quenching - a good example of a method surviving in the corner where its weakness does not apply. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: A

The alkali metals have low excitation energies and are appreciably excited even in a cool flame, so their emission is easily measured without any lamp. Refractory elements are not atomised, transition metals have gaps too large, and non-metals are outside the technique. That one chemical family's low transition energy makes an entire simple instrument viable for it, and useless for everything else, follows directly from the Boltzmann factor. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: B

With no source to match and only a filter to select the strong alkali lines, the instrument reduces to a burner, a filter and a detector. Its flame is cooler, samples are prepared as usual, and it measures one element at a time. That a technique restricted to a few easy elements can be built for a fraction of the cost is why flame photometers remain in clinical laboratories long after more capable instruments became available. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Answer: C

Sodium and potassium are present at millimolar levels and are exactly the elements flame emission handles best, which is why the technique persisted in clinical use. Lead and cadmium need a furnace, iron and copper are usually done by absorption, and mercury by cold vapour. Matching a technique to the concentration and the element together is what puts each measurement on the right instrument.

Answer: D

A plasma at seven thousand kelvin excites every element at once, and a spectrometer disperses their lines onto an array, so a full survey takes a single aspiration. The instrument is far more complex and expensive, samples must still be in solution, and interferences exist though fewer. Measuring many analytes in one operation is worth a great deal when samples are numerous, which is where the technique took the work. Checking the units of each quantity catches a wrong formula before the arithmetic begins.