Atomic Absorption Spectroscopy Questions and Answers

Answer: C

The first two are correct and the third misstates what a spike tests: recovery of a known addition tests the whole procedure for losses and matrix suppression, not the calibration's shape. Linearity is checked with a series of standards. Each validation experiment answers one specific question, and using one to justify a claim it does not support is a common way for a method to look better validated than it is.

Answer: D

The first three are correct and the fourth is not, so three match. Duplicates establish precision, how repeatable a result is, and say nothing about whether it is right - two identical wrong answers are perfectly possible. Distinguishing precision from accuracy is the oldest lesson in analytical chemistry and the one most often forgotten when a set of close results looks convincing.

Answer: A

The pairing is A-P, B-Q, C-R. Each atomiser demands the sample in a different form and quantity, and that requirement often decides the choice before sensitivity is even considered - a scarce sample rules out the flame whatever its detection limit. Matching the atomiser to what is available, as well as to what must be measured, is the practical first question.

Answer: B

At one part per million the flame's fifty parts per billion detection limit is ample, and its ten seconds per sample against two minutes decides a large batch outright. The furnace's sensitivity is simply not needed. Both do reach the level, which is why the third option is tempting, but it ignores the throughput column that the question's word batch points at. Choosing the least capable instrument that meets the requirement is what keeps a laboratory productive.

Answer: C

This is cold vapour, so named because no flame or furnace is needed - mercury alone has enough vapour pressure at room temperature. Hydride generation serves arsenic and its relatives, and a plasma is an emission source. A technique built around one element's unique physical property will only ever serve that element, which is why it has its own name rather than being a variant of the general method. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: D

A wider slit admits more of the lamp's unabsorbable emission, which behaves as stray light and worsens both sensitivity and linearity. The other three all reduce the detection limit, by increasing signal, reducing the blank and reducing noise respectively. That a change admitting more light can make a measurement worse is counter-intuitive until it is remembered that only some of that light can be absorbed. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: A

Excess fuel creates a reducing environment that discourages oxide formation, which helps elements such as chromium and molybdenum that would otherwise be tied up. A lean flame is hotter and better for some elements but not all, and neither height nor uptake is set by the ratio. Tuning the flame's chemistry as well as its temperature is part of optimising a method, and the best ratio differs from element to element. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: B

Burning nearer stoichiometric gives a hotter, cleaner flame with less carbon and lower background emission, which suits elements that atomise readily and do not form stubborn oxides. Reducing conditions come from a rich flame, and uptake and path length are unchanged. Two settings offering opposite chemistries means the choice is a real optimisation rather than a default, and the data sheet for each element usually states which. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: C

Turning the slot out of line with the beam reduces the path length through the atoms, lowering the absorbance and bringing an over-range sample back on scale without dilution. Optical clearance, stability and uptake are not what changes. It is the same lever a shorter cuvette provides in solution photometry, and it trades sensitivity for range in exactly the same way.

Answer: D

Restricted uptake delivers fewer atoms per second and delivers them irregularly, so the reading is both low and unsteady. Flame temperature, background correction and the lamp are unaffected. Because a partial blockage mimics a genuine low result, checking the uptake rate by timing a measured volume is a routine that catches it before a batch of samples is reported wrongly.