Forensic Chemistry

The components of a chromatography system are arranged in the order of the fluid's path.
Step 1: The Source. The process starts with the solvent that will carry the sample.
A. Mobile phase reservoir: This holds the solvent (mobile phase) that is pumped through the system.

Step 2: Protection. Before the main separation, the expensive main column is protected.
B. Guard column: This is a small, disposable column placed before the main column to filter out impurities and particles that could damage the separation column.

Step 3: The Main Process. This is where the chemical separation of the sample components occurs.
C. Separation column (or analytical column): This is the heart of the system, where the components of the mixture are separated based on their interaction with the column's stationary phase.

Step 4: The Result. After separation, the components must be detected.
D. Detector: This device measures the components as they exit the column, producing a signal that is recorded as a chromatogram.
The correct sequence for the flow path is A B C D.

Step 1: Understand the challenge. Analyzing large, fragile biomolecules (like proteins and DNA) with mass spectrometry requires "soft" ionization techniques that don't destroy the molecule, and an analyzer that can handle high mass-to-charge (m/z) ratios.

Step 2: Evaluate the options.
(1) Quadrupole(Q)-Time-of-flight (TOF): This describes a hybrid analyzer (Q-TOF), not a combination of an ionizer and analyzer.
(2) MALDI-TOF: This is a classic and highly effective combination. MALDI is a soft ionization technique where the biomolecule is co-crystallized with a matrix, which absorbs laser energy and gently transfers charge to the analyte. TOF is a mass analyzer that separates ions based on the time it takes them to fly through a tube, and it has a very high mass range, making it perfect for large biomolecules.
(3) & (4) These options list only analyzers, not the required combination of an ionizer and an analyzer.
Conclusion: MALDI-TOF is the correct combination for analyzing biomolecules.

Sensitivity refers to the lowest concentration of a substance that an instrument or technique can reliably detect. The goal is to arrange the given options from least sensitive to most sensitive.
Step 1: Identify the least sensitive techniques.

E. HPLC-RI (Refractive Index Detector): A universal detector that measures changes in the refractive index of the mobile phase. It is known for its relatively poor sensitivity.
B. TLC (Thin-Layer Chromatography): A manual separation technique where detection is often by visual inspection (e.g., under a UV lamp). Its sensitivity is low, typically in the microgram range.
While HPLC-RI is generally considered the least sensitive, the provided correct option starts with TLC (B), followed by RI (E).

Step 2: Identify the mid-range sensitivity technique.

C. HPLC-PDA (Photo Diode-Array Detector): A UV-Vis detector that is much more sensitive than RI or TLC for compounds that absorb light.

Step 3: Identify the high-sensitivity techniques.

A. GC-ECD (Electron Capture Detector): An extremely sensitive detector, but it is selective for compounds containing electronegative atoms (like halogens). For these specific compounds, its sensitivity can be in the femtogram ( g) range.
D. GC-QToF (Gas Chromatography - Quadrupole Time-of-Flight): A high-resolution mass spectrometer. Modern mass spectrometers are highly sensitive universal detectors, often capable of reaching picogram to femtogram detection levels for a wide range of compounds. A QToF is generally considered one of the most sensitive instruments in a forensic lab.

Step 4: Construct the sequence. Following the provided correct option (2), the sequence is B E C A D. This represents an increasing order of sensitivity: TLC