Chromatography—Effect of Slow, Large-Volume Injections on Peak Quality and Separation In liquid or gas chromatography, what is the most likely outcome on peak shape and separation (resolution) when a relatively large sample volume is introduced via a slow injection onto the column?

Introduction / Context:
Chromatographic resolution depends on column efficiency, selectivity, and retention. The injection process, particularly the volume and rate at which sample is delivered to the head of the column, strongly influences initial band width. A slow injection of a large volume typically broadens the starting band, degrading separation quality.

Given Data / Assumptions:

• Injection is performed as a comparatively slow introduction.
• Sample volume is larger than optimal for the column dimensions and phase ratio.
• All other parameters (mobile phase, temperature, flow) are unchanged.

Concept / Approach:
Resolution (Rs) is inversely affected by extra-column and injection-related dispersion. When the sample occupies the column inlet for an extended time, longitudinal diffusion and convection spread the analyte plug before partitioning reaches steady-state. The result is broader peaks and a lower plate count, reducing Rs even if selectivity remains constant.

Step-by-Step Solution:

Verification / Alternative check:
Instrument method development guidelines recommend fast, narrow injections (small volumes, strong-to-weak solvent matching) to minimize injection-band dispersion. Empirically, switching to a smaller, faster injection improves peak sharpness and Rs.

Why Other Options Are Wrong:

• Non-linear detector response usually results from excessive analyte concentration or detector saturation, not merely slow, large-volume injection.
• Increased or constant resolution contradicts the physics of band broadening at the inlet.
• Improved symmetry is not guaranteed; overloading and solvent mismatch often worsen tailing or fronting.

Common Pitfalls:
Confusing sample mass overloading (concentration effect) with volumetric/injection-profile dispersion; both can degrade resolution but via different mechanisms.

Final Answer:
Decreased resolution