Paper: CSIR-NET June 2015 · Subject: Inorganic Chemistry · Chapter: Analytical Chemistry · Topic: Analytical Chemistry – General · Marks: 2 · Difficulty: Medium
Differential pulse polarography (DPP) is more sensitive than D.C. Polarography (DCP). Consider following reasons for it:
1. Non-faradic current is less in DPP in comparison to DCP
2. Non-faradic current is more in DPP in comparison to DCP
3. Polarogram of DPP is of different shape than that of DCP
Correct reason(s) is/are:
(a)1 and 3
(b)2 and 3
(c)2 only
(d)1 only
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
In DPP the current is sampled twice — just before each pulse and again near the end of the pulse, after the charging (non-faradaic) current has decayed. Plotting the difference Δi cancels most of the residual charging current, so the non-faradaic background is far smaller than in DC polarography while the faradaic signal is enhanced. Statement 1 is therefore the reason for the higher sensitivity; statement 2 is false. Statement 3 is true as a fact (DPP gives a peak-shaped curve, DCP a sigmoidal wave), but the shape is a consequence of recording Δi and improves resolution — it is not the cause of the higher sensitivity. Correct reason: 1 only — option (d).