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 refers to the lowest concentration of an analyte that an instrument can reliably detect. We need to order these techniques from least sensitive to most sensitive.
Step 1: Order the techniques from least to most sensitive.
- E. HPLC-RI (Refractive Index Detector): Generally considered one of the least sensitive detectors in chromatography. It is universal but has poor detection limits.
- B. TLC (Thin-Layer Chromatography): This is a visual, manual technique. Its sensitivity is relatively low, typically in the microgram range. It is generally more sensitive than RI but less sensitive than most other instrumental detectors.
- D. GC-TCD (Thermal Conductivity Detector): A universal but moderately sensitive detector for GC. Less sensitive than FID or ECD.
- C. HPLC-PDA (Photo Diode-Array Detector): A UV-Vis detector that offers good sensitivity for compounds that absorb UV light. Generally more sensitive than TCD.
- A. GC-ECD (Electron Capture Detector): This is an extremely sensitive and selective detector for compounds containing electronegative atoms (like halogens in pesticides). It is one of the most sensitive detectors available.

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