Forensic Instrumentation and Spectroscopy Questions and Answers

Answer: C

The mass spectrometric detector in HPLC gives structural and molecular weight information about the eluted solute, option C. It ionises each solute as it leaves the column and measures the mass to charge ratio of the ions, from which the molecular mass and fragments are found. The electrochemical detector (A) measures the current from oxidation or reduction, the fluorescence detector (B) measures emitted light, and the refractive index detector (D) measures a change in the refractive index of the eluent, and none of these gives structure.

Answer: A

The key gives Clarke and Overman, option A, for the first systematic presentation of the neutron activation analysis method. The other names are linked with other techniques: Martin and Synge (B) are known for partition chromatography, for which they received a Nobel Prize in 1952, and Henry and Pascal (C) and Piobert and Pascal (D) are not associated with neutron activation analysis. The answer rests on the key.

Answer: D

Radioactive elements emit alpha rays, beta rays and gamma rays, so the answer is all of the above, option D. Alpha rays are helium nuclei, beta rays are electrons or positrons, and gamma rays are high energy electromagnetic radiation. Each of options A, B and C names only one of the three kinds of emission, so none of them is the full answer. Alpha particles are stopped by a sheet of paper, beta particles by a thin sheet of aluminium, and gamma rays need dense shielding such as lead.

Answer: A

The current that flows in a UV-Vis detector (a photomultiplier or photodiode) even when no light is falling on it is called the dark current. It comes from thermal emission of electrons inside the detector, and instruments correct for it by measuring a dark reading before the sample is measured.

"False current", "true current" and "pseudo current" are not standard terms for this detector signal, so they are wrong.

Answer: C

An exciter filter is part of the fluorescence microscope. It sits in the illumination path and lets through only the short-wavelength light that excites the fluorescent specimen, while the barrier (emission) filter then blocks that light and passes the fluorescence to the eye.

A polarising microscope uses a polariser and analyser, a phase-contrast microscope uses a phase plate and annular diaphragm, and a transmission electron microscope uses electron lenses and no optical filters of this kind. None of them uses an exciter filter.

Answer: A

Water is used as the neutron moderator in neutron activation analysis at a TRIGA reactor. TRIGA fuel contains hydrogen in the zirconium hydride, and the light water around the core slows fast neutrons down to thermal energies, which is what activation analysis needs.

Ethanol, chloroform and acetone are organic solvents that are not used as moderators in a reactor, so they are wrong. The moderator is important because activation analysis depends on thermal neutrons, which are far better at capturing into the sample nuclei than fast neutrons.

Answer: B

In capillary electrophoresis the bulk movement of the electrolyte through the tube is caused by electro-osmotic flow. The charged inner wall of the fused silica capillary attracts counter-ions, and under the applied voltage this layer drags the whole solution towards the cathode.

"Micro-osmatic" and "macro-osmatic" flow are not recognised terms, and since one of the listed flows is correct, "none of the above" is wrong.

Answer: A

For a simple microscope the magnification at the near point is 1 plus D divided by f, where D is 25 cm and f is the focal length. With f equal to 1 cm the value is about 26, and when the image is at infinity it is 25, so the range is 25 to 26.

The figures of 30 to 35, 40 to 45 and 50 to 55 would need a much shorter focal length, so they are wrong. The formula is the standard one for a simple magnifying glass, and it shows that a lens of 1 cm focal length is a powerful magnifier of about 25 to 26 times.

Answer: A

Cell windows made of sodium chloride and similar alkali halide crystals are transparent to infrared radiation, so they are used in IR spectrometry. Glass and quartz absorb in the infrared, which is why alkali halide windows are chosen. UV spectrometry uses quartz cells, and Raman spectrometry and atomic absorption do not use sample cells of this type. So IR spectrometry is the answer.

Answer: D

In X-ray spectroscopy the atoms can be excited in all three ways listed: by bombardment with high energy electrons, by bombardment with protons or other heavy particles, and by irradiation with X-rays of shorter wavelength (as in X-ray fluorescence). Each of the first three statements is a true method of excitation, so the answer is 'All the above'. Choosing any single option would leave out two valid methods.