HPLC cannot directly determine elemental heavy metals like mercury, requiring techniques like AAS or ICP-MS instead. The correct answer is option D.

Question Breakdown

This MCQ tests HPLC limitations versus capabilities, crucial for analytical biochemistry in GATE Life Sciences exams.

Option Analysis

• A. Identify the various pigments from a leaf extract: Possible. HPLC separates chlorophylls/carotenoids using reverse phase columns with UV-Vis detection.

• B. Separate organic pesticides: Routine HPLC application via C18 columns for pesticide residue analysis in food/environmental samples.

• C. Determine the caffeine content in coffee samples: Standard quantitative HPLC method using UV detection at 273 nm with caffeine standards.

• D. Determine the mercury content in a fish sample: Cannot. HPLC analyzes organic compounds, not elemental mercury (requires atomic spectroscopy like AAS/ICP-MS for metal quantification).

Introduction
High performance liquid chromatography (HPLC) cannot be used to determine the mercury content in a fish sample, as it analyzes organic molecules rather than elemental metals. HPLC excels at organic separations like pigments and caffeine but requires atomic techniques for heavy metal detection in biochemistry and food safety testing.

HPLC Capabilities vs Limitations

Perfect for Organic Analysis:

• Pigments: Reverse phase HPLC separates plant chlorophylls by polarity

• Pesticides: Multi-residue methods quantify ng/g levels

• Caffeine: Validated USP methods for beverages

Heavy Metal Limitation:
HPLC detectors (UV, fluorescence, MS) cannot atomize mercury for detection. Sample digestion + AAS/ICP-MS needed for total Hg in fish tissue.

Technique Comparison

Applications Guide

HPLC dominates pharma QC (99% drug analysis), but switch to atomic spectroscopy for environmental metal monitoring per EPA methods.