Plant Biochemistry

• Chromatographic column efficiency and resolution ($R_s$) are directly governed by the number of theoretical plates ($N$), given by the relationship:
  $$N = \frac{L}{\text{HETP}}$$
  where $L$ is column length and $\text{HETP}$ ($H$) is the height equivalent to a theoretical plate.
• (A) is true: Chromatographic resolution is proportional to $\sqrt{N}$; increasing theoretical plates sharpens elution peaks and improves separation.
• (B) is true: Because $N = L / H$, decreasing HETP increases the number of theoretical plates per unit length, directly improving efficiency.
• (C) is false: Decreasing column height ($L$) reduces $N$ ($N = L/H$), leading to peak broadening and poorer separation.
• (D) is true: According to the van Deemter equation ($H = A + \frac{B}{u} + C\cdot u$), the eddy diffusion term ($A = 2\lambda d_p$) and stationary phase mass transfer term ($C_s \propto d_p^2$) decrease drastically with smaller particle diameter ($d_p$), reducing HETP and maximizing separation efficiency (the basis of HPLC and UPLC).
  
  (F) Hence, (A), (B) and (D) only result in enhanced separation (Option 1).

UV absorption of amino acids at 280 nm is primarily governed by aromatic rings and disulfide bonds:

• Tryptophan (D) has the highest molar extinction coefficient at 280 nm ($\varepsilon_{280} \approx 5,500 \text{ M}^{-1}\text{cm}^{-1}$) due to its indole ring.
• Tyrosine (C) has an intermediate absorption at 280 nm ($\varepsilon_{280} \approx 1,490 \text{ M}^{-1}\text{cm}^{-1}$) due to its phenolic hydroxyl ring.
• Cystine/Cysteine (A) exhibits weak absorption around 280 nm ($\varepsilon_{280} \approx 125 \text{ M}^{-1}\text{cm}^{-1}$ for disulfide bonds).
• Phenylalanine (B) absorbs primarily at 257 nm with virtually negligible absorption at 280 nm ($\varepsilon_{280} \lt 10 \text{ M}^{-1}\text{cm}^{-1}$).

Relationship between Absorbance ($A$) and percentage Transmittance ($\%T$):

$$A = 2 - \log(\%T)$$

Given $\%T = 75\%$:

$$\log(75) = \log(3 \times 25) = \log 3 + 2\log 5 = 0.4771 + 2(0.6990) = 0.4771 + 1.3980 = 1.8751$$ $$A = 2 - 1.8751 = 0.1249 \approx 0.125$$