What would likely cause streaking of developed spots in TLC?

Streaking of developed spots in Thin Layer Chromatography (TLC) can be primarily attributed to a multitude of factors, but one significant cause is the low concentration of the sample. When the concentration is too low, the amount of substance that can be adsorbed on the stationary phase may not be sufficient to produce distinct, separated spots. Instead, the molecules may diffuse outwards more rapidly as the solvent front moves, resulting in streaked or tailing spots rather than well-defined bands.

While other options can also contribute to various issues in TLC, they do not directly lead to streaking in the same manner. For instance, using an inappropriate adsorbent can affect the overall resolution and efficiency of the separation but would not typically cause streaking as observed in low concentration scenarios. Writing with a pen instead of a proper pencil can introduce contaminants or allow the ink to dissolve, affecting the baseline rather than directly influencing the appearance of the spots. Similarly, a high boiling point solvent may have implications on the elution and retention times of the samples but does not directly relate to the streaking of the spots themselves. Therefore, maintaining an appropriate sample concentration is crucial for ensuring clear and distinct spots in TLC analysis.