Atomic Absorption Spectroscopy Questions and Answers

Answer: A

If a sample is more viscous or of different surface tension than the standards, the nebuliser draws it at a different rate and delivers a different number of atoms per second. The other options are spectral, ionisation and background effects. Matching the standards' matrix to the sample's, or using standard additions, addresses it - and the fact that the remedy is the same as for several other interferences is part of why standard additions is so widely used.

Answer: B

Undissociated molecules absorb over broad bands and salt particles scatter light, both of which attenuate the beam without any analyte being present. Analyte relaxation produces emission, which is chopped out, and filler lines and ionisation are separate matters. Because background is broad while the atomic line is narrow, the two can be distinguished by a measurement that responds differently to each - which is exactly what background correction does. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: C

The deuterium lamp's light is broad, so the narrow atomic line removes a negligible fraction of it while the background removes the same proportion as before; subtracting gives the atomic absorption alone. A second element lamp would measure a different line, the flame is not interrupted, and scanning is too slow. Measuring the interference with a probe the analyte barely affects is the general principle, and the width difference is what makes it possible.

Answer: D

A deuterium lamp emits well in the ultraviolet but falls away above about 350 nanometres, so elements measured in the visible are poorly corrected. It is fast enough for a furnace, it corrects scattering as readily as molecular absorption, and one lamp serves every element. Knowing where a correction technique stops working is what prompts the use of the alternative, which in this case is the Zeeman method. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: A

A strong field splits the atomic line into components that shift away from the original wavelength, so with the field on only the background absorbs there and with it off both do. The field does not remove the background, no second lamp is needed, and the flame is not interrupted. Modulating the analyte's own absorption while leaving the background untouched gives a correction at exactly the analytical wavelength, which is its advantage over the deuterium method.

Answer: B

Because the correction is made at exactly the wavelength being measured, structured background that varies across the monochromator's band is handled correctly, which the deuterium method cannot do. It needs a substantial magnet, uses the same line source, and costs considerably more. Correcting at the point of measurement rather than nearby is the more rigorous approach, and the price is the hardware. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: C

The flame emits light at the analytical wavelength too, and modulating the lamp lets the detector respond only to the alternating component, ignoring the flame's steady glow. Detector protection, beam switching and furnace timing are other functions. Separating two signals by making one of them vary in a known way is a general technique, and it is why the amplifier is tuned to the chopping frequency. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: D

The source must emit lead's own resonance line, so a lead cathode is required - and one lamp is needed per element, which is the technique's principal inconvenience. A continuum source cannot match the narrow atomic line, a tungsten lamp emits nothing useful in the ultraviolet, and the flame does no selecting. Multi-element lamps exist, combining several metals in one cathode, but each is still restricted to the elements it contains. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: A

Needing a separate source for each element makes multi-element work slow and lamp storage expensive, which is the main reason inductively coupled plasma emission displaced it for surveys. The flame runs continuously, samples need only be in solution, and the monochromator is simply reset. A limitation that follows from the technique's founding idea - a source matched to the analyte - cannot be engineered away without abandoning that idea. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: B

Plasma emission excites every element simultaneously and disperses their lines onto an array, so a full survey takes one aspiration. Multi-element hollow cathode lamps help a little but still measure one line at a time, and the furnace and cold vapour methods are single-element. Measuring many analytes in one operation is worth a great deal when samples are numerous, which is exactly where the plasma technique took the work. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.