Question

Arrange the instruments in increasing order of their sensitivity:
A. GC-ECD
B. TLC
C. HPLC-PDA
D. GC-TCD
E. HPLC-RI

• A. A, B, C, D, E
• B. B, E, C, A, D
• C. C, E, A, D, B
• D. E, B, D, C, A

Hint:

As a rule of thumb for sensitivity: Universal detectors (RI, TCD) are often less sensitive than selective detectors (PDA, ECD). The \textbf{Electron Capture Detector (ECD)} is famously sensitive for specific classes of compounds like pesticides and PCBs.

Answer 1

The Correct Option is D

Sensitivity defines the lowest analyte concentration an instrument can detect reliably. The following techniques are ordered from least to most sensitive.
Step 1: Order the techniques by sensitivity (least to most).
- E. HPLC-RI (Refractive Index Detector): A less sensitive chromatography detector with poor detection limits, though it is universal.
- B. TLC (Thin-Layer Chromatography): A visual, manual technique with relatively low sensitivity (microgram range). More sensitive than RI, but less than most instrumental detectors.
- D. GC-TCD (Thermal Conductivity Detector): A moderately sensitive, universal GC detector. Less sensitive than FID or ECD.
- C. HPLC-PDA (Photo Diode-Array Detector): A UV-Vis detector; offers good sensitivity for UV-absorbing compounds. Generally more sensitive than TCD.
- A. GC-ECD (Electron Capture Detector): An extremely sensitive and selective detector for compounds with electronegative atoms (e.g., halogens in pesticides). One of the most sensitive detectors available.

Step 2: Sequence.
The sensitivity order (least to most) is: HPLC-RI<TLC<GC-TCD<HPLC-PDA<GC-ECD.
The corresponding letter sequence: E \(\rightarrow\) B \(\rightarrow\) D \(\rightarrow\) C \(\rightarrow\) A.